Season Extension Techniques For Market Gardeners

Season Extension Techniques
for Market Gardeners
HORTICULTURE TECHNICAL NOTE
National Sustainable Agriculture Information Service
www.attra.ncat.org
Abstract: Market gardeners can grow crops year-round with season extension techniques. Cultural practices, plastic
mulches, row covers, and low tunnels provide growers with earlier, later, and higher-quality produce that can capture
more markets and demand higher prices. High tunnels or hoophouses, which are essentially unheated greenhouses, have
gained increased interest around the country in the past 10 years. Many growers now consider hoophouses essential to
the success of their market gardens; they are the focus of research projects, workshops, and new manuals. This publication
describes these season extension techniques and provides sources for equipment, supplies, and further information.
Revised by Janet Bachmann
NCAT Agriculture Specialist
January 2005
©2005 NCAT
Introduction
Market gardeners use a variety of techniques
to extend the growing season. Since season
extension has a long history, current techniques
involve both rediscovery and innovation. Gar-
deners through the centuries have learned to use
available materials to produce earlier crops in
the spring, grow cool-season crops in summer,
maintain production well into the fall, and even
harvest crops through the winter. Time-hon-
ored methods include cold frames heated with
manure, masonry walls or stone mulch as heat
sinks, and cloches (glass bell jars) to protect in-
dividual plants. Improvements in glass quality
were big news for season extenders of the 18th
and 19th centuries.(Ashton, 1994) More recently,
plasticulture (use of plastics in agriculture) has
greatly extended the possibilities for year-round
production. Plastic ﬁlm mulches, drip irriga-
tion, row covers, low tunnels, and high tunnels
High tunnels protect high value crops. Photo
by Janet Bachmann
Table of Contents
Introduction ........................................................................................................... 1
Cultural Practices ................................................................................................... 2
Plasticulture for Season Extension ............................................................................ 6
Economics of Season Extension .............................................................................. 21
References ........................................................................................................... 22
Further Resources ................................................................................................ 24
ATTRA is the national sustainable agriculture information service operated by the National Center for Appropriate Technology,
through a grant from the Rural Business-Cooperative Service, U.S. Department of Agriculture. These organizations do not
recommend or endorse products, companies, or individuals. NCAT has ofﬁces in Fayetteville, Arkansas (P.O. Box 3657,
Fayetteville, AR 72702), Butte, Montana, and Davis, California.

or hoophouses, help to protect crops from the
weather. The use of plastic in horticultural crop
Related ATTRA Publications
production has increased dramatically in the past
decade. High tunnels are springing up around
the country, as more and more market gardeners
Compost Heated Greenhouses
see them as essential to their operations.
Greenhouse and Hydroponic Vegetable
Beneﬁts from year-round production include
Resources on the Internet
year-round income, retention of old customers,
gain in new customers, and higher prices at times
of the year when other local growers (who have
Low-cost Passive Solar Greenhouses
only unprotected ﬁeld crops) do not have pro-
duce. Other potential beneﬁts of season extension
Root Zone Heating
technologies are higher yields and better quality.
In addition, with year-round production you can
provide extended or year-round employment for
Solar Greenhouse Resource List
skilled employees whom you might otherwise
lose to other jobs at the end of the outdoor grow-
Specialty Lettuce and Greens:
ing season. Disadvantages include no break in
Organic Production
the yearly work schedule, increased management
demands, higher production costs, and plastic
Scheduling Vegetable Plantings for
disposal problems.
Continuous Harvest
Eliot Coleman, a market gardener in Maine who
uses various techniques to grow vegetables
year-round, summarizes the contribution season
higher-elevation site only a few miles away can
extension makes to sustainability.
easily have a 4- to 6-week longer growing season.
A site on the brow of a hill, with unimpeded air
. . . to make a real difference in creating a local food
drainage to the valley below, would be ideal
system, local growers need to be able to continue
where season extension is an important consider-
supplying “fresh” food through the winter months
ation. (In more mountainous areas, temperatures
. . .[and] to do that without markedly increasing
drop as elevation increases.)
our expenses or our consumption of non-renewable
resources.(Coleman, 1995)
In northern states, land with a southern aspect
is the best choice for early crops, as south-facing
The information in this publication and in the
slopes warm up sooner in the spring. Further-
materials listed as Further Resources can help
more, the closer to perpendicular the southern
you analyze the beneﬁts and costs of season ex-
slope is to the angle of sunlight, the more quickly
tension techniques on your farm.
it warms.
South-facing slopes may not be advantageous
Cultural Practices
in the southern U.S., where soil is likely to be
relatively shallow, poor in soil fertility, and low
in accumulated organic matter. If there has to
Almost all plants beneﬁt from increased early-
be a choice between a sunnier aspect and native
and late-season warmth. Many cultural tech-
soil quality, the latter wins out, especially in the
niques can modify the microclimate in which a
South, where winters and early springs are not
crop is grown, without using structures or covers,
as cold as in the North.
though some of these techniques require long-
term planning.
Soils and Moisture Content
Site Selection
Soils can affect temperature because their heat
storage capacity and conductivity vary, depend-
Garden site selection is very important for ex-
ing partly on soil texture. Generally, when they
tended-season crop production. Cold air, which
are dry, sandy and peat soils do not store or con-
is heavier than warm air, tends to settle into val-
duct heat as readily as loam and clay soils. The
leys on cold nights, limiting the growing season
result is that there is a greater daily temperature
there. In areas of relatively low elevation, a
range at the surface for light soils than for heavier
PAGE 2
//SEASON EXTENSION TECHNIQUES FOR MARKET GARDENERS

soils, and the minimum surface temperature is
lower. Darker soils often absorb more sunlight
Smudge Pots and Wind Machines
than light-colored soils and store more heat.
Consequently, areas with lighter-colored soils
Smudge pots that burn kerosene or other fuels
(and no ground cover) are more prone to frost
are placed throughout vineyards or orchards to
damage.(Snyder, 2000)
produce smoke. The smoke acts like a blanket
to keep warm air from moving away from the
Bare soil absorbs and radiates more heat than soil
ground. The smoke is also a signiﬁcant source
covered with vegetation. Although the radiated
of air pollution, and smudge pots are rarely used
heat helps protect against frost, cover crops pro-
anymore.(Atwood and Kelly, 1997) Today, using
vide many other beneﬁts. Mowing to keep the
oil and gas heaters for frost control in orchards is
ground cover short provides a compromise.
usually in conjunction with other methods, such
as wind machines, or as border heat (two or three
In addition, moist soil absorbs and radiates more
rows on the upwind side) with undertree sprin-
heat than dry soil, because water stores consider-
kler systems.(Evans, 1999; Geisel and Unruh,
able heat. To maximize this effect, water content
2003; Snyder, 2000)
in the upper one foot of soil where most of the
change in temperature occurs must be kept near
Specialty cut ﬂower growers Pamela and Frank
ﬁeld capacity.(Snyder, 2000)
Arnosky in Texas have a lot of experience deal-
ing with wide ﬂuctuations in temperature, and
in a recent article they describe various methods
Irrigation
for protecting high-value crops. They give this
description of wind machines.
Overhead sprinklers, furrow, and drip irrigation
can be used to protect crops from frost. Sprinklers
Cold air is heavier than warm air, and on a still
are turned on when the temperature hits 33°F.
night, the cold air will sink below the warm air
When the water comes in contact with plants, it
and actually ﬂow downhill. This is what happens
begins to freeze and release heat. As ice forms
when people say you have a “frost pocket.” As
around branches, vines, leaves, or buds, it acts as
cold air ﬂows downhill, it gets trapped in valleys
an insulator. Although the level of protection is
and low spots. Even a row of trees can hold cold
high, and the cost is reasonable, there are several
air in a pocket. Unless your farm is perfectly ﬂat,
disadvantages. If the system fails in the middle
you probably have a frost pocket somewhere, and
of the night, the risk of damage can be quite high.
you can avoid trouble by planting that spot later in
Some plants are not able to support the ice loads.
the spring, or with hardy plants.
Large amounts of water, large pipelines, and big
pumps are required. Water delivered to a ﬁeld
As the cool air sinks, the warm air is pushed up,
via drip and furrow irrigation, however, can
and settles in a layer just above the ﬁeld as an “in-
keep temperatures high enough to prevent frost
version layer.” This is a pretty neat phenomenon
damage without the same risks.(Evans, 1999;
Snyder, 2000)
Orchard-Rite Ltd. wind machines protect crops from frost, and with added Agri-Cool™
System protects apple crops from hot weather. Photo courtesy of Orchard-Rite, Ltd.
// SEASON EXTENSION TECHNIQUES FOR MARKET GARDENERS
PAGE 3

that occurs on perfectly still nights. The inversion
Cultivar Selection
layer can be quite warm, and often is not very far
off the ground. . . .
Cultivar selection is important for early crop
production. The number of days from planting
In big orchard operations, you will often see giant
to maturity varies from cultivar to cultivar, and
fans on towers among the trees. These fans are there
some cultivars germinate better in cool soil than
to take advantage of the trapped inversion zone.
others. Staggered planting dates can be combined
They mix the warm air above and prevent the cold
with the use of cultivars spanning a range of ma-
air from settling among the trees. They are super-
turity dates to greatly extend the harvest season
expensive, but so is losing a crop. Fans like this only
for any one crop. Early-maturing cultivars are
work in a still, radiational frost.(Arnosky, 2004)
very important in going for the early market,
though in many cases the produce will be smaller.
More information about wind machines is
Some later-maturing cultivars also have better
available from contacts listed under Further
eating qualities and yields than earlier cultivars.
Resources.
Information on varieties adapted to your area is
available from local growers, seed catalogues,
trade magazines, Cooperative Extension, and
Windbreaks
resources listed at the end of this publication.
Windbreaks decrease evaporation, wind damage,
and soil erosion, and provide habitat for natural
Brett Grohsgal, who co-owns Even’ Star Organic
enemies of crop pests. They are also an important
Farm with his wife, Dr. Christine Bergmark, in
part of season extension, helping to create pro-
southern Maryland, says that seed saving and
tected microclimates for early crops. Windbreaks
genetic management are keystones of their winter
should run perpendicular to (across) the prevail-
cropping system. They started with purchased
ing direction of early-season winds.(Hodges and
seed, but after several years of careful selection
Brandle, 1996) Existing stands of trees can be
used, but choose trees for windbreaks carefully,
and seed saving, they have their own supply of
so that shading, competition for water and nutri-
seed for crops adapted to their harsh local winter
ents, and refugia for plant pests do not become
weather.(Grohsgal, 2004)
problems.
Shade
Fall-planted cover crops of small grains (rye,
barley, winter wheat) can serve as windbreaks
Although season extension usually brings to
the following spring; at plow-down, strips are
mind an image of protecting plants from the cold,
left standing every 30 to 40 feet and cut or tilled
modifying temperatures in mid-summer can also
under when no longer needed. Each strip should
be important. Shade over a bed can create a cool
be the width of a small-grain drill (10 to 12 feet).
microclimate that will help prevent bolting and
However, small winter-grains may be too short to
bitterness in heat-sensitive crops such as lettuce
constitute an effective windbreak for early spring
and spinach, make it possible to grow warm-
crops. Top-dressing with compost will help
weather crops in areas with very hot summers,
ensure a good stand. Another option is to plant
and hasten germination of cool-weather fall
perennial grass windbreaks that will maintain
crops. Some growers provide cooling shade by
protection through winter and early spring.
growing vines such as gourds on cattle panels
or similar frames placed over the beds. Shade
These are only general guidelines; experimen-
fabrics, available from greenhouse- and garden-
tation and adaptation are necessary to ﬁnd the
supply companies, can be fastened over hoops in
best solution for a particular situation. Other
summer to lower soil temperatures and protect
windbreaks include snow fences, commercial
crops from wind damage, sunscald, and drying.
windbreak materials, brush piles, stone walls,
Placing plants under 30 to 50% shade in midsum-
old fencerows or hedges, shrubs, berry brambles,
mer can lower the leaf temperature by 10°F or
and even overgrown ditches. In any case, wind-
more.(Bartok, 2004)
breaks should not be allowed to interfere with
down-slope air drainage and should allow for
Commercial shade fabrics are differentiated by
some circulation to prevent air stagnation and
how much sunlight they block. For vegetables
frost pockets.(Lamont, 1996; Hodges and Brandle,
like tomatoes and peppers, use 30% shade cloth
1996)
in areas with very hot summers. For lettuce, spin-
ach, and cole crops, use 47% in hot areas, 30% in
northern or coastal climates. Use 63% for shade-
PAGE 4
//SEASON EXTENSION TECHNIQUES FOR MARKET GARDENERS

loving plants. (The maximum
shade density—80%—is often used
over patios and decks to cool people
as well as plants).(Peaceful Valley,
2004) See the ATTRA publication
Specialty Lettuce and Greens: Organic
Production for more on growing let-
tuce in hot weather. Shade houses
can also provide frost protection
for perennials and herbs during
winter. Temperatures inside can
be as much as 20°F higher than
outdoors.(Bartok, 2004)
Silver Tufbell from Peaceful Valley
Farm Supply is a specially devel-
oped alternative to woven shade
fabric. It is impregnated with sil-
ver-ﬁnish aluminum for very high
Plastic mulch can increase yield and quality of potatoes.
light as well as infra-red (heat) reﬂection. Photo courtesy Penn State Center for Plasticulture.
This, combined with a close weave, gives 45%
shading during the day, but reﬂects heat back
ing a leaf canopy to shade out germinating weed
to the crop at night. Silver Tufbell is especially
seedlings. Transplants also avoid other pests that
suited for sun- and heat-sensitive crops. The
attack germinating seeds and young seedlings,
reﬂective surface also deters many pests, espe-
such as fungal diseases, birds, and insects.
cially whiteﬂies and aphids, from approaching
the crop.(Peaceful Valley, 2004)
Multiple Cropping
Steve Upson, who has been working with hoop-
houses at the Noble Foundation in Oklahoma,
Planting more than one crop on the same bed or
began installing Kool-Lite Plus brand poly ﬁlm,
row in one year intensiﬁes the cropping schedule.
in attempts to keep the houses cooler in the
Immediately after one crop is harvested, another
summer. He says this ﬁlm, which blocks solar
is planted. Dr. Charles Marr and Dr. William
infra-red radiation, has kept temperatures up to
Lamont (1992) list the following advantages of
12°F cooler during the afternoon and evening.
multiple cropping, and conclude “if you can’t
He says although you can expect to pay 75%
triple crop, then you certainly can consider
more for Kool-Lite Plus, the additional cost can
double cropping.”
be justiﬁed, considering the costs associated with
the use of shade fabric.(Upson, 2002)
• Cost savings. Money spent on plastic mulch,
drip irrigation lines, and other equipment
covers three crops instead of one.
Transplants
• Higher gross per acre. In his triple cropping
Use of transplants (versus direct seeding) is
ﬁeld trials, Lamont realized gross returns of
another key season-extension technique. Some
$13,000 to 15,000 per acre.
crops have traditionally been transplanted, and
recent improvements in techniques have expand-
• Improved cash flow. Multiple harvests
ed the range of crops suited to transplant culture.
throughout the season can provide income
Transplants provide earlier harvests by being
at critical times and distribute returns more
planted in a greenhouse several weeks before it
evenly over a longer period.
is safe to direct-seed the same crop outdoors. If
a grower uses succession planting or multiple
• Risk management. Multiple cropping pro-
cropping (i.e., follows one crop with another in
vides a hedge against the loss of a crop to
the same spot), transplants provide extra time for
freezes, hailstorms, and other crises.
maturing successive crops. Transplants hit the
ground running, with a 3 to 4 week head start on
• Increased productivity. Small areas of land
the season. Transplanting aids in weed control by
are thus made more productive, a great boon
getting a jump on the weeds and by quickly form-
in areas where cropland is scarce or costly.
// SEASON EXTENSION TECHNIQUES FOR MARKET GARDENERS
PAGE 5

Table 1. Spring-Fall Planting Sequences for North Carolina
Please note that crops in the same family never follow each other in the same field or bed in the same
year. The same rule applies to triple cropping sequences.
Spring
Fall
Peppers
Summer squash, cucumbers, or cole crops
Tomatoes
Summer squash, cucumbers, or cole crops
Summer squash
Tomatoes or cole crops
Eggplant
Summer squash
Cucumbers
Tomatoes
Muskmelons
Tomatoes
Watermelons
Tomatoes
Honeydews
Tomatoes
Cole crops
Summer squash, pumpkins, muskmelons, or tomatoes
Cauliflower
Summer squash, pumpkins, muskmelons, or tomatoes
Snap beans
Summer squash, pumpkins, muskmelons, or tomatoes
Southern peas
Summer squash, pumpkins, muskmelons, or tomatoes
Lettuce
Summer squash, pumpkins, muskmelons, or tomatoes
Sweet corn
Summer squash, tomatoes, or cucumbers
Strawberries
Tomatoes, summer squash, cucumbers, or pumpkins
(Sanders, 2001)
Table 1 shows examples of dou-
Table 2. Examples of triple cropping sequences
ble cropping sequences from
North Carolina.(Sanders, 2001)
Spring
Summer
Fall
Table 2 shows examples of triple
Cole crops
Summer squash
Tomatoes
cropping sequences suitable for
plasticulture in Kansas.(Marr
Lettuce
Cucumbers
Tomatoes
and Lamont, 1992) For related
Sweet corn
Cucumbers
Tomatoes
information, see the ATTRA
publication Scheduling Vegetable
(Marr and Lamont, 1992)
Plantings for Continuous Harvest.
• Cleaner, higher-quality produce
Plasticulture for Season
• More efﬁcient use of water resources
Extension
• More efﬁcient use of fertilizers
• Reduced soil and wind erosion (though
During the past 10 years there has been an explo-
erosion may increase in un-mulched paths
sion in the use of plastics in agriculture. The term
between rows)
“plasticulture” is used to describe an integrated
• Potential decrease in disease
system that includes—but is not limited to—plas-
• Better management of certain insect pests
tic ﬁlm mulches, drip irrigation tape, row covers,
low tunnels, and high tunnels. Some beneﬁts of a
• Fewer weeds
comprehensive plasticulture system include:
• Reduced soil compaction and elimination
of root pruning
• Earlier crop production (7 to 21 days
earlier)
• The opportunity for efﬁcient double or
triple cropping (Lamont, 1996)
• Higher yields per acre (2 to 3 times higher)
PAGE 6
//SEASON EXTENSION TECHNIQUES FOR MARKET GARDENERS

Disadvantages of Plasticulture:
The Disposal Dilemma
Costs and management time will both increase with the use of plasticulture, but if it’s done well, the
higher productivity and profit should more than compensate. The most serious problems associated with
plasticulture have to do with removal from the field and disposal. Machines are commercially available
to remove plastic mulch from the field (Zimmerman, 2004; Holland, 2004) and to roll and pack it into
bales, but for smaller-scale growers this is probably not an option. Other obstacles to recycling include
dirt on the plastic, UV degradation, the high cost of collecting and sorting, and a lack of reliable end-
use markets. But recycling technologies and initiatives are evolving. Dr. William Lamont, an advocate
of plasticulture, envisions a future when growers will remove, chop, and pelletize field plastics for use
as a fuel. Lamont and others at The Penn State Center for Plasticulture are currently testing a heater
manufactured in Korea that burns plastic pellets made from waste plastics of all types. Dennis DeMatte,
Jr., who as manager of the Cumberland County (New Jersey) Improvement Authority works with New
Jersey’s greenhouse plastic film recycling program, stated that since the program was initiated in 1997,
the CCIA has recycled approximately 80 percent of the film collected. From 1997 through 2002, the
state collected about 1,120 tons of film.(Kuack, 2003) Web sites for more information about recycling
agricultural or greenhouse-related plastic products include:
The Penn State Center for Plasticulture
www.plasticulture.org/newsletters/ASP_April04.pdf
Cumberland County Improvement Authority
www.ccia-net.com
Agriculture Container Recycling Council
www.acrecycle.org
USAg Recycling Inc.
www.usagrecycling.com
Cornell University Environmental Risk Analysis Program
http://environmentalrisk.cornell.edu/C&ER/PlasticsDisposal/AgPlasticsRecycling/
Plastic Mulches
squash can also be established as transplants into
plastic, if earliness and reduced environmental
Plastic mulches have been used commercially on
stress are required. In the Southwest, spring mel-
vegetables since the early 1960s. Muskmelons,
ons are direct seeded then covered with plastic
tomatoes, peppers, cucumbers, squash, eggplant,
strips to accelerate germination and develop-
watermelons, sweet corn, snap beans, southern
ment. At the three to four leaf stage, the plastic
peas, pumpkins, and okra will all ripen earlier
is removed.(Guerena, 2004)
and produce better yields and fruit quality when
grown on plastic mulch.
Small-scale market gardeners will probably lay
down plastic mulch by hand. Tim King, market
Plastic mulches have helped growers in extreme
gardener near Long Prairie, Minnesota, has been
northern and high-altitude climates harvest
using a system of raised beds, drip irrigation,
heat-loving crops that were previously impos-
plastic mulch, and fabric row-cover tunnels since
sible for them to grow. In the northeastern U.S.
1986. He says that although doing everything by
small acreages of sweet corn are established by
hand is very labor intensive, they are very pleased
transplanting into plastic mulch for an early
with the ﬂexibility this gives them to “hybridize”
crop. Broccoli, cauliﬂower, pumpkin, and winter
the parts of the system in various ways. It also al-
// SEASON EXTENSION TECHNIQUES FOR MARKET GARDENERS
PAGE 7

lows them to reuse much of the material a second
same advantages as smooth black plastic. The
and even a third season.(King, 2002)
pattern helps to keep the mulch ﬁtted tightly to
the bed. For plastic mulch to be most effective,
Mechanical application can save time. Many
it is important that it be in contact with the soil
growers have found that a simple tractor-pulled
that it covers. Air pockets act as insulation that
mulch layer will reduce overall costs and help
reduces heat transfer.
ensure a uniform installation that will resist wind
damage. Plans are available for a mulch layer
Clear plastic mulch will allow for greater soil
that can be built in a farm shop (Thompson et al.,
warming than colored plastic. It is generally used
2004), and the machines are also commercially
in the cooler regions of the United States, such as
available. They can also be designed to install a
New England. Clear plastic increases soil tem-
drip irrigation line at the same time.(Zimmerman,
peratures by 8 to 14ºF at a depth of 2 inches, and
2004; Holland, 2004) Plants or seeds can be set
by 6 to 9°F at a depth of 4 inches.(Orzolek and
through slits or holes in the plastic by hand or
Lamont, no date) A disadvantage is that weeds
with a mechanical transplanter. Labor savings
can grow under the clear mulch, while black
from mechanical transplanters are signiﬁcant,
mulch shades them out. Therefore, clear plastic
even on limited acreages.
is generally used in conjunction with herbicides,
fumigants, or soil solarization. Organic growers
For successful plant establishment with plastic
may want to experiment with clear plastic to ﬁnd
mulch, it is important that beds be level, the plas-
out whether weeds become a real problem. The
tic is tightly laid, drip irrigation tape is placed in
mulch’s beneﬁt to the crop may outweigh the
a straight line in the center of the bed, and water
competition from weeds.(Coleman, 1995)
is applied through the irrigation system immedi-
ately after transplanting. Never use plastic mulch
White, coextruded white-on-black, or silver reﬂect-
without irrigation.
ing mulches can result in a slight decrease in soil
temperature. They can be used to establish a crop
when soil temperatures are high and any reduc-
Certified organic producers should be aware that
tion in soil temperatures is beneﬁcial.
organic standards place certain restrictions on
Infrared-transmitting (IRT) mulches provide the
the use of plastic mulches. For example, PVC
weed control properties of black mulch, but they
plastics may not be used as mulches or row
are intermediate between black and clear mulch
covers. Also, plastic mulches must be removed
in warming the soil. IRT mulch is available in
from the field before they begin decomposing—
brown or blue-green.
which would seem to eliminate photodegradable
films from organic production.
Red mulch performs like black mulch, warming the
soil, controlling weeds, and conserving moisture,
with one important difference. In Pennsylvania
experiments, tomato crops responded with an av-
Plastic mulches are available in a number of col-
erage 12% increase in marketable fruit yield over
ors, weights, and sizes for various needs. Many
a 3-year period. There appears to be a reduction
come as 3– to 5–foot wide rolls that can be laid
in the incidence of early blight in plants grown on
over soil beds with a tractor and mechanical
red mulch, compared with plants grown on black
mulch layer. Extensive research with colored
mulch. When environmental conditions for plant
mulches has been conducted at the Horticulture
growth are ideal, tomato response to red mulch
Research Farm, Rock Springs, Pennsylvania, by
is minimal. Other crops that may respond with
staff of The Pennsylvania State University Cen-
higher yields include eggplant, peppers, melons,
ter for Plasticulture. (See Further Resources for
and strawberries.(Bergholtz, 2004) (Red mulch
contact information.)
also suppresses nematodes. See the ATTRA
publication Alternative Nematode Control.)
Black plastic mulch is the most commonly used.
It suppresses weed growth, reduces soil water
Additional colors that have been investigated
loss, increases soil temperature, and can im-
include blue, yellow, silver, and orange. Each
prove vegetable yield. Soil temperatures under
reflects different radiation patterns into the
black plastic mulch during the day are gener-
canopy of a crop, thereby affecting plant growth
ally 5°F higher at a depth of 2 inches and 3°F
and development. Increased yield was recorded
higher at a depth of 4 inches compared with
for peppers grown on silver mulch, cantaloupe
bare soil.(Sanders, 2001) Black plastic embossed
on green IRT or dark blue mulch, and cucum-
ﬁlm has a diamond-shaped pattern. It has the
bers and summer squash on dark blue mulch,
PAGE 8
//SEASON EXTENSION TECHNIQUES FOR MARKET GARDENERS

compared with black. Insect activity can also be
on-farm experiments to explore alternatives to
affected: yellow, red, and blue mulches increase
plastic. They compared soil temperatures and
peach aphid populations; silver repels certain
tomato growth using various mulches, including
aphid species and whiteflies and reduces or
black plastic, Planters Paper, and recycled kraft
delays the incidence of aphid-borne viruses in
paper. Plastic, paper, and organic mulches all
crops.(Orzolek and Lamont, no date)
improved total yields of tomatoes grown in the
trials, when compared with tomatoes grown on
Photodegradable ﬁlm has much the same qualities
bare soil.(Schonbeck, 1995; Anderson, 1995)
as other black or clear plastic ﬁlm, but is formu-
lated to break down after a certain number of
Recycled kraft paper is available in large rolls at
days of exposure to sunlight. The actual rate of
low cost. Participants in the experiment were
breakdown depends on temperature, the amount
concerned that it would break down too quickly.
of shading from the crop, and the amount of
To retard degradation, they oiled the paper. This
sunlight received during the growing season.
resulted in rather transparent mulch and, as with
Buried edges of the ﬁlm must be uncovered and
clear plastic, soil temperatures were higher than
exposed to sunlight. Use of photodegradable
under black plastic. Weeds also grew well under
ﬁlm eliminates some of the disposal problems
the transparent mulch. To reduce weed growth
associated with regular plastic, but is not with-
and to keep the soil from becoming too hot, the
out problems, and its availability has decreased
experimenters put hay over the oiled paper sev-
rather than expanded during the past ﬁve years.
eral weeks after it was laid.
A representative of one company that no longer
offers photodegradable mulch says they discon-
Planters Paper is a commercially available paper
tinued the product because the breakdown was
mulch designed as an alternative to plastic. It
not consistent. Photodegradable mulch is not
comprises most of the beneﬁts of black plastic
allowed for use in organic production.
ﬁlm and has other advantages. It is porous to
water. Left in the soil, or tilled in after the grow-
ing season, it will degrade. Tomatoes grown with
Biodegradable Mulches
this mulch showed yields and earliness similar
to tomatoes grown in black polyethylene mulch,
Biodegradable plastics are made with starches
even though the latter resulted in slightly higher
from plants such as corn, wheat, and potatoes.
soil temperatures. Planters Paper, however, is
They are broken down by microbes. Biodegrad-
considerably more expensive than black plastic.
able plastics currently on the market are more
It does not have the stretchability of plastic, and
expensive than traditional plastics, but the lower
it tends to degrade prematurely along the edges
price of traditional plastics does not reﬂect their
where it is secured with a layer of soil. The paper
true environmental cost. Field trials in Australia
is then subject to being lifted by the wind. Rebar,
using biodegradable mulch on tomato and pep-
old pipe, or stones—rather than soil—can be used
per crops have shown it performs just as well
to secure the edges.(Bergholtz, 2004)
as polyethylene ﬁlm, and it can simply be
plowed into the ground after harvest.(Anon,
2002) Researchers with Cornell Univer-
sity also found that biodegradable mulches
supported good yields, but the ﬁlms they
used are not yet commercially available
in the U.S.(Rangarajan et al, 2003) Bio-
Film is the ﬁrst gardening ﬁlm for the U.S.
market. Made from cornstarch and other
renewable resources, it is 100% biodegrad-
able. Bio-Film is certiﬁed for use in organic
agriculture by DEBIO, the Norwegian con-
trol and certiﬁcation body for organic and
biodynamic agricultural production, and is
available from Dirt Works in Vermont. (See
Further Resources.)
Paper mulch can provide beneﬁts similar Penn State Center for Plasticulture trial of potatoes grown with
to plastic and is also biodegradable. An colored plastic mulch, drip irrigation, and floating row covers.
innovative group in Virginia carried out Photo courtesy Penn State Center for Plasticulture.
// SEASON EXTENSION TECHNIQUES FOR MARKET GARDENERS
PAGE 9

Melons, more and earlier
crops without support. (Crops with tender,
exposed growing points, such as tomatoes and
peppers, are exceptions. To prevent damage
One study, based on three years of field trials in
from wind abrasion, the cover should be sup-
Utah, found that clear plastic mulch increased
ported with wire hoops.) The spun-bonded
watermelon yield by 20%, while using the mulch
fabric is permeable to sunlight, water, and air,
and provides a microclimate similar to the inte-
and a row cover increased the yield by 44%, in
rior of a greenhouse. Plants are protected from
comparison with melons raised without plasticul-
drying winds by what amounts to a horizontal
ture. The mulch also allows for earlier planting.
windbreak, and the covers give 2 to 8°F of frost
Dr. Alvin Hamson, the primary author of the study,
protection. In addition to season extension, ad-
recommends covering the cultivated beds with
vantages include greater yields, higher-quality
clear plastic a week or two before transplanting.
produce, and exclusion of insect pests.
Then set the transplants into slits cut into the plas-
Floating row covers are available in various
tic. The mulch wil trap enough heat to protect the
weights ranging from 0.3 to 2 ounces per square
melon plants down to an air temperature of 27ºF.
yard. The heavier the cover, the more degrees
Some further tips from Dr. Hamson: Transplant
of frost protection it affords. Sizes range from
three-week-old seedlings into the field (harden
widths of 3 to 60 feet and lengths of 20 to 2,550
them of first) about the same time apple blossoms
feet. Wider covers are more labor-efﬁcient, as
there is less edge to bury per covered area. Du-
open in your area. If you plan to use a floating
rability is related to weight, type of material, and
row cover in addition to the mulch, you can set
the additives used.
out transplants a week before apple bloom. Be
sure to remove the row cover a week before the
The lightest covers are used primarily as insect
melons begin to flower, so that bees can pollinate
barriers. They can protect crops such as cabbage
them, and remove it gradually—leave the cover
and broccoli from loopers and cabbage worms
by excluding the egg-laying moths. Eggplant,
off for a few more hours each day for a week.
radishes, and other favorites of the ﬂea beetle are
Dr. Hamson recommends the same early planting
easily protected by ﬂoating row covers. Be sure to
technique for summer squash.(Long, 1996)
rotate crops in ﬁelds or beds planted under row
covers, since overwintering insects from a previ-
Another study, done at an experiment station in
ous crop can emerge under the cover.(Hazzard,
Connecticut, involved multiple cropping of spe-
1999) Various diseases spread by insect vectors
such as aphids and leaf hoppers are prevented
cialty melon transplants using black plastic mulch
as long as the cover remains in place. Disadvan-
and floating row covers. Yields from these beds
tages to the lighter covers are that they are easily
were up to three times higher than yields from
damaged by animals and are seldom reusable.
beds planted in plastic mulch without the row
The lightest covers have a negligible effect on
cover. The earliest-yielding cultivars in this study
temperature and light transmission.
were Passport (galia) and Acor (charentais), both
Medium-weight covers are the most commonly
developed with shorter days to maturity for use
available. They are used to enhance early ma-
in northern climates. These specialty melons are
turity, increase early yields and total yields,
larger than cantaloupe and fetch a higher price.
improve quality, and extend the season or make
Accounting for the added expense of row covers,
possible the production of crops in areas where
the researchers concluded that “row covers not
they could not otherwise be grown. They also
only increased early fruit and total fruit, but prof-
serve as insect barriers. Crops commonly grown
with protection of medium-weight covers include
itability is about 6-fold greater when melons are
melons, cucumbers, squash, lettuce, edible-pod
grown for retail or wholesale.”(Hill, 1997)
peas, carrots, radishes, potatoes, sweet corn,
strawberries, raspberries, and cut ﬂowers.
Heavier covers, those exceeding 1 ounce per
Floating Row Covers
square yard, are used primarily for frost and
freeze protection and where extra mechanical
Floating row covers are made of spun-bonded
strength and durability are required for ex-
polyester and spun-bonded polypropylene and
tended-season use. The microclimate created
are so lightweight that they “ﬂoat” over most
by heavier covers is similar to that created by
PAGE 10
//SEASON EXTENSION TECHNIQUES FOR MARKET GARDENERS

Floating row covers
can be used again in
the fall. This some-
times involves modi-
fying the technol-
ogy. When ﬂoating
row covers are used
for spring crops, the
covers are removed
before the crops ma-
ture, while with fall
crops the covers re-
main on the mature
plants. In windy
c o n d i t i o n s t h i s
sometimes results in
abrasion of the plant
leaves, which can
mar the appearance
of a leafy crop. In
Floating row covers are available in various weights and sizes. Photo courtesy of
that case, the cover
Ken-Bar.
could be supported
on wire hoops or
medium-weight covers, but they can be reused
bowed ﬁberglass rods, so it no longer rubs against
for three to four seasons or more.
the vegetable crop.(Coleman, 1995)
Floating row covers can be installed manually or
Row covers should be stored away from sun-
mechanically. Immediately after transplanting or
light as soon as they are removed from the ﬁeld.
direct seeding, lay the covers over the area and
Many have been treated to resist degradation
weigh down or bury the edges. Small-diameter
by UV light; whether or not that is the case, they
concrete reinforcing bar (rebar), cut to manage-
will last longer if stored carefully in a dark, dry
able lengths, is excellent for weighting the edges.
place. Fold or roll the covers in a systematic way
Enough slack should be left in the cover to allow
to make them easy to unfurl for the next season’s
the crop to grow. Row covers placed over crops
use.(Hazzard, 1999)
growing on bare soil create a favorable environ-
ment for weed germination and growth. Peri-
Hoop-Supported Row Covers
odic removal of the cover for hand cultivation is
not practical. Weed control can be a signiﬁcant
(Low Tunnels)
problem under row covers, unless they are used
in combination with plastic or other mulches.
Row covers made of clear or white polyethylene
are too heavy to ﬂoat above the crop, so they
In self-pollinated crops, or leafy vegetables such
are supported by hoops. Dimensions vary, but
as lettuce or cabbage, the covers can be left on
a typical structure is 14 to 18 inches high at the
for most of the production period. One caution
apex and wide enough to cover one bed. They
when growing tomatoes or peppers under covers
are commonly used in combination with black
is in regard to heat—temperatures that rise above
plastic mulch for weed control. Hoop-supported
86°F for more than a few hours may cause blos-
row covers are often called low tunnels. They
som drop.(Wells, 1992) With insect-pollinated
offer many of the same beneﬁts as ﬂoating row
crops, such as melons, squash, or cucumbers, the
covers, but are not permeable to air or water and
covers must be removed at ﬂowering to allow
are more labor-intensive. There are several types
for insect pollination. The covers may, however,
of low tunnels.
be replaced after the crop has been pollinated.
Removing the covers should be considered a
Slitted row covers have pre-cut slits that provide
hardening-off procedure. Over the course of
a way for excessive hot air to escape. At night
a few days, keep the covers off for longer and
the slits remain closed, reducing the rate of con-
longer periods. Final removal is best done on a
vective heat loss and helping to maintain higher
cloudy day, preferably just before a rain. Plants
temperatures inside the tunnel.
will suffer more transition shock if exposed to
sun and wind.
Punched row covers have small holes punched
// SEASON EXTENSION TECHNIQUES FOR MARKET GARDENERS
PAGE 11

Cold Frames
Traditional low struc-
tures such as cold
frames and cloches
are continually be-
ing modified by in-
novative gardeners
and garden supply
manufacturers. Al-
though cold frames
work well in pro-
tecting crops in cold
weather, construction
costs are high com-
pared to plasticulture
systems. For special
situations, many pub-
lications contain plans
for cold frames, solar
pods, and other small
Slitted row covers have pre-cut slits that provide a way for excessive hot air to es- portable structures.
cape. Photo courtesy of Ken-Bar.
Solar Gardening, by
Leandre and Gretchen
about 4 inches apart to ventilate hot air. The
Poisson, listed under Further Resources, is one
punched covers trap more heat than the slitted
such publication. A more recent article on cold
tunnels. They are best for northern areas and
frames can be found in the November 2004 issue
must be managed carefully to avoid overheating
of Fine Gardening magazine.(Vargo, 2004)
crops on bright days. They are useful for peppers,
tomatoes, eggplant, most cucurbits, and other
warm-season crops that grow upright.
High Tunnels
Tunnels that use two 3-foot wide plastic sheets
High tunnels, also called hoop houses, have been
stapled together at the top are commonly used
attracting a lot of attention in the past few years,
by farmers growing trellised crops such as cherry
as more and more market gardeners have come
tomatoes, long beans, and bitter melons. These
to consider high tunnels essential tools in their
tunnels are more expensive to put up, but they
operations. A high tunnel is basically an arched
require little equipment investment. Most of
or hoop-shaped frame covered with clear plastic
the work to put them up is done by hand.(Ilic,
and high enough to stand in or drive a tractor
2004)
through. Traditional high tunnels are completely
solar heated, without electricity for automated
Hoops for supporting slitted or punched row
ventilation or heating systems. Crops are grown
covers are often made from 10-gauge galvanized
in the ground, usually with drip irrigation. Com-
wire. The pieces are cut to 65 to 75 inches long.
pared to greenhouses, high tunnels are relatively
Each end is inserted about 6 to 12 inches deep
inexpensive, ranging in price from $1.50 to $3.00
on each side of a row or bed to form a hoop over
per square foot—and even less for the Haygrove
it. Hoops are spaced 5 to 8 feet apart—or less.
multibay tunnels discussed below.
Tim King, a market gardener in Minnesota, cuts
hoops 3 to 4 feet long and spaces them 2 feet
High tunnels are used extensively in Europe,
apart in the beds.(King, 2002) The covers are
Asia, and the Middle East. Although high tun-
anchored on each edge with soil. Tunnels can
nels are not used as much in the United States
be set by hand or with machines that resemble
as in other parts of the world, interest here is
plastic mulch layers.
growing rapidly. Universities and agricultural
organizations around the country are conducting
high-tunnel research, market growers are hosting
workshops on their farms and at conferences, and
more articles are appearing in trade journals and
newsletters.
PAGE 12
//SEASON EXTENSION TECHNIQUES FOR MARKET GARDENERS

Right: The most critical components
of hoop house strength are the end
walls. Below: At the Noble Founda-
tion, wood end-posts fabricated from
two 2- by 6-inch boards, corrugated
fiberglass. Photos courtesy of Noble
Foundation.
Universities and Foundations Conducting High Tunnel Research (Lamont, 2003)
University or Foundation
Contact
Phone
E-mail
Pennsylvania State University Center
Bill Lamont
814-865-7118
wlamont@psu.edu
for Plasticulture
http://plasticulture.cas.psu.edu
Ohio State University
Matt Kleinhenz
330-263-3810
kleinhenz1@osu.edu
University of New Hampshire
Brent Loy
603-862-3216
jbloy@christa.unh.edu
Rutgers University
A.J. Both
732-392-9534
both@aesop.rutgers.edu
University of Maryland Cooperative
Bryan Butler
bb113@umail.umd.edu
Extension
University of Missouri-Columbia
Louis Jett
573-884-3287
jettl@missouri.edu
Kansas State University
Ted Carey
913-438-8762
tcarey@oznet.ksu.edu
University of Nebraska
Laurie Hodges
402-472-1639
lhodges@unl.edu
University of Minnesota
Terrance Nennich
218-694-2934
nenni001@umn.edu
Michigan State University
John Biernbaum
517-353-7728
biernbau@msu.edu
Noble Foundation, Oklahoma
Steve Upson
580-223-5810
sdupson@noble.org
Healthy Farmers Healthy Profits Proj-
Astrid Newenhouse
608-262-1054
astridn@facstaff.wisc.edu
ect, University of Wisconsin
University of Kentucky
Brent Rowell
859-257-3374
browell@ca.uky.edu
// SEASON EXTENSION TECHNIQUES FOR MARKET GARDENERS
PAGE 13

universities and private foundations. Titles
and ordering information for these are pro-
vided under Further Resources.
High tunnels have had a tremendous im-
pact on season extension. Market garden-
ers say the structures pay for themselves
in one season.
• Crops grown in hoophouses have
higher quality and are larger than
those grown in the ﬁeld.
• Crops grown in hoophouses can hit
the market early when prices are high
and help to capture loyal customers
for the entire season.
• Hoophouses allow certain crops to be
grown throughout the winter, pro-
viding a continuous supply to markets
(and tables) the entire year.
Crops that have been grown in high tunnels
include specialty cut ﬂowers, lettuce and
other greens, carrots, tomatoes, peppers,
squash, melons, raspberries, strawberries,
blueberries, and cherries. Although high
tunnels provide a measure of protection
from low temperatures, they are not frost
protection systems in the same sense that
greenhouses are. On average, tunnels per-
mit planting about three weeks earlier than
outdoor planting of warm season crops.
Haygrove Tunnel with Cherries. Photo courtesy of Haygrove
They also can extend the season for about
a month in the fall. Earlier plantings and
Tunnels.
later harvests would require a supplemental
heating system.
Several manuals on hoophouses have been pub-
lished recently. They give details on construction,
crop production, economics, and sources for
Location and Site Preparation
supplies, equipment, and additional information.
Some of these were written by market gardeners
Alison and Paul Wiediger of Au Naturel Farm in
who have built and are using hoophouses. Oth-
south-central Kentucky grow winter vegetables
ers were published as a result of research done at
in 8,500 square feet of high tunnels. In regard to
locating a hoophouse, they advise other growers
to put it close to the house. Especially on cold
The High Tunnels Web site, www.
days, the shorter the walk from the house to the
hoophouse, the more pleasant the trip will be—
hightunnels.org, is another valu-
and the more likely you will be to make it. The
able resource. At this site, re-
Wiedigers advise other growers to prepare the
searchers, Extension specialists,
site so that the ground is level from side to side,
professors, students, technicians,
and has no more than 3% slope from end to end.
and growers are collaborating to
Avoid wet or shady areas and obstructions to
share their experience and knowl-
ventilation. Make sure drainage around the site
is good. You don’t want water running through
edge about the use of high tunnels
the house every time it rains.(Wiediger, 2003)
in the Midwest.
PAGE 14
//SEASON EXTENSION TECHNIQUES FOR MARKET GARDENERS

Orientation
is taller than the other, and the third vent is at the
top of the tall side. This is the most expensive of
Dan Nagengast of Wild Onion Farm in eastern
these three designs. See Further Resources for
Kansas says the orientation (east-west or north-
information.
south) depends on your location. Manufacturers
recommend orienting the house to capture the
Strength is important. Heavy-gauge galvanized
most light in winter. For locations north of 40°
steel pipe is best for hoops. Setting the hoops
latitude, the ridge should run east to west. For
four feet rather than any further apart is also
locations south of 40° latitude, the ridge should
recommended. Growers in snowy climates might
run north to south. At any latitude, gutter-con-
choose a peaked-roof structure instead of the
nected or closely spaced multiple greenhouses
quonset style.(Bartok, 2002) The most critical
will get more light if they are aligned north-south
components of a hoop house for strength are the
because they avoid the shadow cast by structures
end walls.(Upson, 2004) At the Noble Founda-
to the south.(Byczynski, 2003) Dr. Lewis Jett,
tion, wood end-posts fabricated from two 2- by
in Columbia, Missouri, says that a high tunnel
6-inch boards, corrugated ﬁberglass panels for
should be oriented perpendicular to prevailing
end-wall glazing, and industrial steel frame doors
winds: in regard to orientation of a high tunnel,
with heavy-duty latches, provide long-lasting
sunlight is less important than ventilation.(Jett,
end walls.
2004)
The most economical covering is 6-mil green-
house grade, UV-treated polyethylene, which
Design and construction
should last three to ﬁve years. Do not use plastic
that is not UV-treated—“It will fall apart after half
A high tunnel is not difﬁcult to build. The most
a season.”(Mattern, 1994)
common design uses galvanized metal bows at-
tached to metal posts driven into the ground 4
Roll-up sides used on many high tunnels provide
feet apart—a traditional quonset style structure.
a simple and effective way to manage ventilation
Carol A. Miles and Pat Labine in Washington
and control temperature. The edge of the plastic
offer construction details for a 10-foot by 42-foot
is taped to a one-inch pipe that runs the length
structure that can be built for $350.(Miles and
of the tunnel. A sliding “T” handle is attached
Labine, 1997) See Appendix I.
to the end of the pipe so that the plastic can be
rolled up as high as the hip board. Ventilation
The High Tunnel Production Manual, published
is controlled by rolling up the sides to dispel the
by The Pennsylvania State University Center for
heat. Depending on temperature and wind fac-
Plasticulture, details the construction and use
tors, the two sides may be rolled up to different
of 17- by 36-foot tunnels using a gothic arch de-
heights.
sign developed by Penn State. (They chose this
smaller size for research purposes.) The center
Coleman (1995) gives the following advice for
section of the end walls can be opened up for
dealing with wind.
easy access by machinery.(Lamont, 2003) Con-
struction details only are shown in Appendix II,
Wind whipping and abrasion can be a serious prob-
Design and Construction of the Penn State High
lem. No matter how carefully the cover is tightened
Tunnel.
when it is ﬁrst put on, it always seems to loosen.
There are two ways to deal with this. The simplest
The Hoop House Construction Guide, by Steve Up-
is to run stretch cord over the top of the plastic from
son of the Noble Foundation, provides details for
one side to the other…. One cord between every
three designs: quonset, straight wall, and triple
fourth rib is usually sufﬁcient. The tension of the
side-vent. Upson says the quonset structure is
stretch cord will compensate for the expansion and
generally the least expensive to purchase. While
contraction of the plastic due to temperature change
satisfactory for producing low growing crops,
and will keep the cover taut at all times. The sec-
trellised crops can’t be grown close to the sides.
ond solution is to cover the tunnel with two layers
Straight wall designs provide unhindered in-
of plastic and inﬂate the space between them with
ternal access along the sides of the house, while
a small squirrel cage fan. This creates a taut outer
permitting plenty of vertical growing space, but
surface that resists wind and helps shed snow.
because of the additional pipe required, expect to
pay more for materials and to spend more time
on construction. The triple side-vent has vents
on both ends of the tunnel; one side of the house
// SEASON EXTENSION TECHNIQUES FOR MARKET GARDENERS
PAGE 15

Missouri cut flower grower builds a solar-powered hoophouse
When Bryan Boeckmann of Westphalia, Missouri, decided to start cultivating cut flowers, a high tunnel
seemed like the natural choice. But he had a problem: He couldn’t always be in Westphalia to make the
required adjustments. Temperatures in such a structure can easily get too high on a sunny day, and the
grower must be on hand to open the vents.
“I work full time for the fire department in Jefferson City, and the temperature in a high tunnel can change
a lot in a 24-hour period,” he said. “I had to have something I could rely on. Fortunately, necessity is
where most good ideas come from.” Boeckmann’s good idea was to use solar power to automatically
raise and lower the side curtains on his tunnel. His project was funded by a grant from the Missouri
Department of Agriculture.
Jim Quinn, the MU extension researcher who helped with the project, said Boeckmann was inspired by
existing technology in poultry barns. “He had seen how poultry curtains work, and he thought, ‘Why can’t
I do the same thing with a high tunnel and use solar power?’” The curtains are made of white, woven,
tarp-like material. They are pulled up to close the sides and lowered to open the sides of the tunnel.
Quinn said the innovation “is really a nice fit. The times when you need to adjust the curtains are when
there’s a lot of sunny weather, and that’s also when the solar power is available.”
Boeckmann initially hoped to drive the side curtains with conventional electric power, but hooking into
the grid was “cost-prohibitive,” he said. He called on Missouri Valley Renewable Energy (MOVRE), a
firm in Hermann, Missouri, to design and build a solar unit. Using mostly used parts, MOVRE owner
Henry Rentz constructed a small building with two solar panels on the roof and an inverter, batteries, and
control panel within.
“I found some used stuff for Bryan because I wanted him to succeed in what he was doing,” said Rentz.
“Those batteries alone would have cost $1,600 new. I basically did it to show people something that
already works.”
The system succeeded beyond their expectations. “In June, when we had that extended period of rain,
that system ran for 11 days without sun, “ Rentz said.
“It’s fairly simple, “ Boeckmann said. “Once you’ve initially set it up, typically you don’t have to mess with
it. You just have to set the thermostat.” The thermostat in the hoop house senses temperature and, at
a set point, triggers a mechanism that very slowly raises or lowers the plastic side curtains. “The reason
it moves so slowly is to give the temperature in the building a chance to adjust,” he said. “It takes it 15
minutes to go all the way up. You can do it manually really fast, if a storm is coming.”
Boeckmann also uses solar power to drive his irrigation pump—“a little bitty pond pump that doesn’t
eat up a lot of juice.”
He believes his innovations could boost the already growing interest in high tunnel construction. “There’s
good reason for the interest,” he said. “The difference they make is phenomenal, considering it’s just a
sheet of plastic stretched over a frame. They just keep improving them.“
For more information, contact Jim Quinn at 573-882-7514 or by e-mail at
quinnja@missouri.edu.(Rose, 2004)
PAGE 16
//SEASON EXTENSION TECHNIQUES FOR MARKET GARDENERS

Irrigation is essential for adequate and timely wa-
65°F. A maximum/minimum thermometer is
tering. Watering can be done by hand, through
a great aid in keeping tabs on temperature.
a trickle or drip system, or by overhead emitters.
The Pennsylvania State Center for Plasticulture
Twenty feet by 96 feet is a size commonly
High Tunnel Production Manual discusses the
used by market growers. This size allows ef-
advantages of drip irrigation from water being
ﬁcient heating and cooling, efﬁcient growing
delivered directly to the soil around the crops.
space, and adequate natural ventilation. Lynn
Byczynski and Dan Nagengast who grow spe-
• Efﬁcient water and fertilizer use
cialty cut ﬂowers and vegetables in Zone 5 near
• Reduced weed competition in areas outside
Lawrence, Kansas, have ﬁve hoophouses, each
the beds
20 by 96 feet. They purchased Polar Cub cold
• Ability to simultaneously irrigate and work
frames from Stuppy Greenhouse Company.
inside tunnels
They chose Stuppy not because it was the
only greenhouse manufacturer, but because
• Reduction in disease potential because
it was the closest, so shipping costs were least
water doesn’t get on the leaves
expensive. The cost for two houses was $3,250,
including the metal frames, four-year poly
If you choose trickle irrigation, use one line per
covering, wiggle wire to attach the poly to the
row, or depending on the crop, one line per
frames, and shipping. Lumber to install the
double row. If the soil is adequately fortiﬁed
roll-up sides and poly-covered endwalls cost
with nutrients, supplemental feeding might not
an additional $1,600. They also paid a neigh-
be necessary; however, nitrogen can be applied
bor $300 to prepare the site with a bulldozer
through the trickle system.
and laser leveling device. In their ﬁrst year,
the hoophouses produced more than twice
The manual also discusses overhead irrigation
what they cost. The record of crops grown,
and provides details on how to construct an over-
planting and harvest dates, and revenue per
head system. This allows irrigation water to be
square foot is shown in Table 3.(Byczynski,
applied evenly to the entire soil surface. It can be
2003) Additional details, including photos that
used to leach salts from tunnel soils or to establish
show the construction of a Stuppy’s Polar Cub
and grow cover crops within the tunnel.
cold frame at Wild Onion Farm, can be found
in The Hoophouse Manual: Growing Produce and
A ﬂoor covering of a single sheet of 6-mil black
Flowers in Hoophouses and High Tunnels. See
plastic or landscape fabric provides several
Further Resources.
advantages. It warms the soil, controls weeds,
greatly reduces evaporation of soil moisture, and
Alison and Paul Wiediger also use a commer-
serves as a barrier against diseases in the soil that
cially available 20- by 96-foot high tunnel, in
could infect plant parts above
ground. Secure the edges
(sides and ends) of the plastic
to prevent wind from blowing
the plastic over the plants.
Temperature management
using the roll-up sides is
critical. On sunny mornings,
the sides must be rolled up to
prevent a rapid rise in tem-
perature. Tomato blossoms,
as mentioned earlier, will be
damaged when temperatures
go above 86°F for a few hours.
Even on cloudy days, rolling
up the sides provides ventila-
tion to help reduce humid-
ity that could lead to disease
problems. The sides should
be rolled down in the evening Hoophouses at Wild Onion Farm. Photo courtesy of Wild Onion Farm.
until night temperatures reach
// SEASON EXTENSION TECHNIQUES FOR MARKET GARDENERS
PAGE 17

Hoophouse production at Wild Onion Farm
Revenue per
Crop
Date planted
Dates of harvest
square foot
Fall-planted flowers
Delphinium ‘Clear Springs’ and “Bellamosum”
9/28/00
4/26/01-7/26/01
$2.67
Dianthus (Sweet William)
9/25/00
4/24/01-6/1/01
$5.05
Larkspur ‘Giant Imperial’
10/7/00
5/2/01 - 6/10/01
$3.25
Spring-planted flowers
Stock ‘Cheerful’
3/21/00
5/18/00-5/30/00
$1.92
Campanual ‘Champion’
4/1/01
6/3/01-6/30/01
$3.62
Lisianthus
4/12/00
6/26/00-10/8/00
$3.32
Fall-planted vegetables
Arugula
9/27/00
fall, spring
$1.31
Cilantro
9/27/00
fall, spring
$0.95
Chinese cabbage
9/27/00
fall
$1.11
Green onions
9/27/00
fall
$0.61
Leeks
9/27/00
spring
$1.10
Lettuce
9/27/00
fall, spring
$0.40
Mizuna
9/27/00
fall
$0.69
Spring-planted vegetables
Cucumbers
4/12/00
summer
$1.34
Tomatoes
4/12/00
summer, fall
$3.55
Byczynski, 2003
addition to two 21- by 60-foot tunnels. They think
than 100 feet or so may be too long for effective
there is value in building as large a structure as
natural ventilation.
is practical.(Wiediger, 2003)
The Wiedigers use a double layer of 6-mil, 4-year
Most of the growing in this tunnel will be in spring,
poly to cover their tunnels. A small fan blows
fall, and winter when outside temperatures are
air between the two layers to create an insulating
cooler/colder. We believe that both the earth and
barrier against the cold. Construction and man-
the air within the tunnel act as heat sinks when the
agement details can be found in their manual,
sun shines. At night, they give up that heat, and keep
Walking to Spring: Using High Tunnels to Grow
the plants safe. The smaller the structure, the smaller
Produce 52 Weeks a Year. See Further Resources
that temperature “ﬂywheel” is, and the cooler the
for ordering information.
inside temperatures will be.
Haygrove Multibay Tunnel Systems
They also ﬁnd that plants close to the walls do
not grow as well as the plants further from them.
With Haygrove tunnels, innovative growers are
The larger the frame, the larger the percentage of
literally covering their ﬁelds to protect high-value
effective growing area. And most growers want
crops from early and late frost, heavy rain, wind,
more, rather than less, space at the end of one
hail, and disease. The frames also provide sup-
growing season.
port for shade cloth and bird netting.(DeVault,
Twenty feet wide, however, may be as wide as
2004) The British company Haygrove was started
you can get with the inexpensive cold frame type
in 1988 with a little more than two acres of straw-
hoophouses without interior bracing. Longer
berries in hoophouses. By 2002, Haygrove had
expanded to nearly 250 acres of soft fruits, includ-
PAGE 18
//SEASON EXTENSION TECHNIQUES FOR MARKET GARDENERS

ing strawberries, blackberries, red currants, and
cherries, grown under plastic in England and
eastern Europe. They also came up with a new
design for multibay tunnels and sold 3,000 acres
of tunnels throughout Europe. Haygrove tunnels
are now being distributed and used in the U.S.
Haygrove sells tunnels from 18 to 28 feet wide
per bay, with a three bay minimum. There are no
walls between bays. The total length and width
can be whatever the grower desires. Company
representative Ralph Cramer in Lancaster Coun-
ty, Pennsylvania, says he has seen tunnels as short
as 65 feet and as long as 1,100 feet. They have
been used to cover from 1/3 acre to 100 acres (of
blueberries in California). Unlike greenhouses,
Haygrove tunnels don’t need to be built on ﬂat
ground, but can be built on slopes. Cramer says
advantages of the systems include lower cost
and better ventilation.(Cramer, 2004) One acre of
Haygrove tunnels costs about 55 cents per square
foot, or about $24,000.(Byczynski, 2002)
North Carolina market gardeners Alex and
Betsy Hitt covered two quarter-acre blocks with
Haygroves in 2004. One block was planted to
specialty cut ﬂowers, the other to organically
grown heirloom tomatoes. Heirlooms have not
been bred to resist foliar diseases, and growing
Ful production in early March at Au Naturel
organically limits fungicide options. Alex was
Farm, lettuces and spinach. Photo courtesy of
pleased with the resulting decrease in plant
Au Naturel Farm.
disease: “We have very severe foliar disease
Haygrove tunnels covering large area. Photo courtesy of Haygrove Tunnels.
// SEASON EXTENSION TECHNIQUES FOR MARKET GARDENERS
PAGE 19

Haygrove tunnel with tomatoes. Photo courtesy Haygrove Tunnels.
problems on our tomatoes in the ﬁeld and tradi-
Leitz Farms in Sodus, Michigan, covered 10 acres
tionally would pick a crop for about ﬁve weeks,
of tomatoes this year to help control growing
and then it would be dead. With the Haygroves,
conditions. Fred Leitz, one of four brothers who
we picked from the same number of plants for
run the family farm, said the plants look healthier
almost 10 weeks and picked and sold 35% more
than the ones outside and show no sign of dis-
fruit than last year.”(Hitt, 2004) Hitt also noticed
ease. Their operation was featured on the front
less disease in the Haygroves, compared with
page of Vegetable Growers News.(Morris, 2004)
single bay tunnels with roll-up sides. He attri-
butes the difference to better ventilation in the
Haygrove tunnels, unlike single bay hoophouses,
Haygroves, since they vent so high, resulting in
are not designed to carry a snow load, so they
less humidity.(Cramer, 2004)
cannot be covered with poly during the winter
in areas that have snow. John Berry, director of
Pennsylvania grower Steve Groff of Cedar Mead-
Haygrove, says “Haygrove tunnels are designed
ow Farm agrees. In 2004, despite the early arrival
to be temporary low-cost structures that can be
of late blight in the eastern United States and
moved with the crop. The key management
Canada, Groff’s six inter-connected bays yielded
task is venting. Unlike conventional single hoop
more than 3,000 25-pound boxes of tomatoes (by
houses, multibay tunnels can be completely
October 11), with seventy percent of them grad-
opened to ensure the crop is not stressed by heat
ing out at No. 1. His unprotected ﬁelds yielded
or humidity.” Strawberries grown with this sys-
only about 25 to 60 percent percent No. 1s. Groff
tem can be picked two to three weeks earlier in
says 2004 was an extremely unusual year, with
the spring; yields of raspberries, blueberries, and
a lot of wet weather. Tunnels allowed him to
strawberries have consistently been 30 percent
reduce fungicide use by more than 50 percent
higher in tunnels, compared with ﬁeld grown
and allowed tomato harvest to begin two to three
berries; and the grade-out percentage for soft fruit
weeks earlier. They also extended the season: On
under the tunnels runs about 90:10 Class A to B,
October 11, Groff was still picking from tomatoes
compared with 75:25 for conventional outdoor
planted in April, and expected to harvest 100 to
production.(Otten, 2003)
200 more 25-pound boxes. (DeVault, 2004, Groff,
2004)
PAGE 20
//SEASON EXTENSION TECHNIQUES FOR MARKET GARDENERS

The mobile high tunnel
practice. It is called a partial budget because it
is not necessary to calculate the expenses that
The “salad days” of season extension were argu-
would be the same for either practice. Steps to
ably in the second half of the 19th century, on
follow in the analysis include:
the outskirts of Paris, where 2,000 or so market
gardens employed cloches and cold frames to
• Decide what crop will be grown using a
produce 100,000 tons of out-of-season produce
season extension technique.
per year. Many of these growers built small
• Decide what season extension technique
trackways on which to move the heavy glass
cloches and frames to different parts of the gar-
will be used.
den. (Poisson, 1994) For the past century, Euro-
• Calculate costs of the new technique,
pean horticulturists have put railcar wheels on
including supplies, rent or purchase of
greenhouses and rolled them on iron rails. The
specialized equipment, labor, water, pest
rails extend two or more times the length of the
management. Allow for extra hours of
greenhouse, making multiple sites available for
labor due to inexperience in the ﬁrst year.
one house. Eliot Coleman describes a sample
cropping sequence for a mobile greenhouse or
• Calculate the added gross income from the
high tunnel.
new technique. Gross income is simply the
price per unit of produce sold multiplied
An early crop of lettuce is started in the greenhouse
by the number of units sold. Income
on Site 1. When the spring climate is warm enough
changes as a result of a change in the price
for the lettuce to ﬁnish its growth out-of-doors, the
received per unit, a change in the number
ends are raised and the house is wheeled to Site 2.
of units sold, or both.
Early tomato transplants, which need protection at
that time of the year, are set out in the greenhouse
• Calculate any reduced expenses associated
on Site 2. When summer comes and the tomatoes
with the change. For example, use of black
are safe out-of-doors, the house is rolled to Site 3
plastic or paper mulch will reduce the
to provide tropical conditions during the summer
need for cultivation or herbicides. Use of
for transplants of exotic melons or greenhouse
ﬂoating row covers will reduce the need for
cucumbers.
other insect pest management operations.
At the end of the summer, the sequence is reversed.
• Add up all the increases and decreases of
Following the melon and cucumber harvest, the
expense and income and calculate the total
house is returned to Site 2 to protect the tomatoes
change in proﬁt.
against fall frosts. Later on, it is moved to Site 1
to cover a late celery crop that was planted after
Speciﬁc information on costs of materials and
the early lettuce was harvested. Then Site 1 is
supplies is available from the companies and
planted to early lettuce again, and the year begins
in the manuals listed under Further Resources.
anew.(Coleman, 1992)
The High Tunnel Production Manual, High-Tun-
Coleman has adapted these practices to his own
nel Tomato Production, The Hoophouse Handbook
garden, replacing the heavy and costly iron
and several Noble Foundation bulletins contain
with more practical wooden rails. He provides
sample budgets for a number of fruits, vegetables,
plans for his mobile high tunnel, and year-round
and cut ﬂowers.
cropping plans, in his book Four-Season Harvest.
It must be remembered that any sample budget is
See Further Resources.
just that—a sample. All market gardeners bring
their own mix of skills, values, and resources
together to build a unique system. According to
Economics of Season
Coleman(1992):
Extension
The secret to success in lengthening the season with-
out problems or failures is to ﬁnd the point at which
One method for determining whether season
the extent of climate modiﬁcation is in balance with
extension techniques can be a profitable ad-
the extra amount of time, money, and management
dition to a farming operation is called partial
skill involved in attaining it. When planning for a
budgeting.(Ilic, 2004) A partial budget requires
longer season, remember the farmer’s need for a
assessment of changes in income and expenses
vacation period during the year. The dark days
that would result from changing to a different
of December and January, being the most difﬁcult
// SEASON EXTENSION TECHNIQUES FOR MARKET GARDENERS
PAGE 21

months in which to produce crops, are probably
Coleman, Eliot. 1995. The New Organic Grow-
worth designating for rest, reorganization, and
er: A Master’s Manual of Tools and Tech-
planning for the new season to come.
niques for the Home and Market Gardener.
2nd Edition. Chelsea Green Publishing,
Lebanon, NH. 270 p.
References
Cramer, Ralph. 2004. Personal communica-
tion.
Anderson, David F. et al. 1995. Evaluation of a
paper mulch made from recycled materials
DeVault, George. 2004. Farming under cover
as an alternative to plastic ﬁlm mulch for
- BIG TIME! The New Farm. August 31.
vegetables. Journal of Sustainable Agricul-
www.newfarm.org/columns/george_devault/
ture. Spring. p. 39–61.
0804haygrove.shtml
Evans, Robert D. 1999. Frost Protection in
Anon. 2002. Making packaging greener: Bio-
Orchards and Vineyards. Northern Plains
degradable plastics. Australian Academy
Agricultural Research Laboratory, Sidney,
of Science.
MT. 20 p. www.sidney.ars.usda.gov/
www.science.org.au/nova/061/061key.htm
Geisel, Pamela, and Carolyn L. Unruh. 2003.
Arnosky, Pamela and Frank. 2004. When frost
Frost Protection for Citrus and Other Sub-
threatens, know what to expect. Growing
tropicals. University of California Divi-
for Market. May. p. 15–17.
sion of Agriculture and Natural Resources
Publication 8100. 4 p.
Ashton, Jeff. 1994. A short tale of the long
http://anrcatalog.ucdavis.edu
history of season extension. The Natural
Farmer. Spring. p. 12–13.
Groff, Steve. 2004. Personal communication.
Atwood, Sam, and Bill Kelly. 1997. Orchard
Grohsgal, Brett. 2004. Winter crops, part 2:
smudge pots cooked up pall of smog. 3 p.
Planting through marketing. Growing for
www.aqmd.gov/monthly/smudge.html
Market. September. p. 9
Guerena, Martín. 2004. Personal communica-
Bartok, John W. 2004. Shade houses provide
tion.
seasonal low-cost protected space. Green-
house Management & Production. May.
Hazzard, Ruth. 1999. Vegetable IPM Message.
p. 56–57.
Vol. 10, No. 1. University of Massachusetts
Vegetable & Small Fruit Program.
Bartok, John W. 2002. Hoop house designs
www.umass.edu/umext/programs/agro/veg-
help ease snow loads. Greenhouse Man-
smfr/
agement & Production. August. p. 75–76.
Articles/Newsletters/pestmessages/may12_
99.html
Bergholtz, Peter. 2004. KEN-BAR Products for
the Grower: Agricultural plastics. KEN-
Hill, David E. 1997. Effects of multiple crop-
BAR, Inc., Reading, MA.
ping and row covers on specialty melons.
www.ken-bar.com
Connecticut Agricultural Experiment Sta-
tion, New Haven. Bulletin 945. October.
Byczynski, Lynn. 2002. A cheaper hoophouse?
12 p.
Growing for Market. October. p. 1, 4–7.
Hitt, Alex. 2004. Personal communication.
Bycynski, Lynn (ed.). 2003. The Hoophouse
Hodges, Laurie, and James R. Brandle. 1996.
Handbook: Growing Produce and Flowers
Windbreaks: An important component in
in Hoophouses and High Tunnels. Fairplain
a plasticulture system. HortTechnology.
Publications. 60 p.
July–September. p. 177–180.
Coleman, Eliot. 1992. The New Organic Grow-
Holland Transplanter Co. 2004. Product infor-
er’s Four-Season Harvest. Chelsea Green
mation. Holland, MI.
Publishing, Post Mills, VT. 212 p.
www.transplanter.com
Ilic, Pedro. 2004. Plastic Tunnels for Early
PAGE 22
//SEASON EXTENSION TECHNIQUES FOR MARKET GARDENERS

Vegetable Production. University of
California Small Farm Center Family Farm
Morris, Christine. 2004. Grower erects 10 acres
Series Publications. 21 p.
of high tunnels to improve crop quality.
www.sfc.ucdavis.edu/Pubs/Family_Farm_Se-
American Vegetable Grower. August. p. 1
ries/
www.vegetablegrowernews.com/pages/2004/
issue04_08/04_08_Leitz.htm
Jett, Lewis. 2004. High Tunnel Tomato Produc-
tion. University of Missouri. 28 p.
Orzolek, Michael D., and William J. Lamont, Jr.
No date. Summary and Recommendations
King, Tim. 2002. Plasticulture without equip-
for the Use of Mulch Color in Vegetable
ment. Growing for Market. April. 2002. p.
Production. The Pennsylvania State Center
1, 4–5.
for Plasticulture. 2 p.
www.plasticulture.org
Kuack, David. 2003. Dennis DeMatte Jr. on
New Jersey’s plastic ﬁlm recycling pro-
Otten, Paul. 2003. High tunnels: Quietly revo-
gram. Greenhouse Management & Produc-
lutionizing high value crops. Northland
tion. July. p. 90–91.
Berry News. p. 11.
Lamont, William J. 1996. What are the com-
Peaceful Valley Farm Supply main catalogue.
ponents of a plasticulture vegetable sys-
2004. Grass Valley, CA.
tem? HortTechnology. July–September. p.
www.groworganic.com
150–154.
Poisson, Leandre and Gretchen. 1994. Solar
Lamont, William J., Michael D. Orzolek, E. Jay
Gardening: Growing Vegetables Year-
Holcomb, Kathy Demchek, Eric Burkhart,
Round the American Intensive Way. Chel-
Lisa White, and Bruce Dye. 2003. Produc-
sea Green Publishing. 288 p.
tion system for horticultural crops grown in
the Penn State high tunnel. HortTechnol-
Rangarajan, Anu, Betsy Ingall, and Mike Davis.
ogy. April–June. p. 358–362.
Alternative Mulch Products 2003. Cornell
University. 4 p.
Lamont, William J., Martin R. McGann, Mi-
http://www.hort.cornell.edu/extension/com-
chael D. Orzolek, Nymbura Mbugua, Bruce
mercial/vegetables/online/2003veg/PDF/
Dye, and Dayton Reese. 2002. Design and
Mulch2003Final.pdf
construction of the Penn State high tunnel.
HortTechnology. July–September.
Rose, Forrest. 2004. Westphalia man builds
p. 447–453.
solar-powered hoophouse. University of
Missouri Extension and Ag Information.
Lamont, WIlliam J. (ed.). 2003.High Tunnel
News release. September 30.
Production Manual. The Pennsylvania State
University. 164 p.
Sanders, Douglas. 2001. Using Plastic Mulch
and Drip Irrigation for Vegetable Produc-
Long, Cheryl. 1996. New ground: Help spring
tion. North Carolina State University
arrive early. Organic Gardening. April.
HIL–33. 6 p.
p. 18–19.
www.ces.ncsu.edu/
Marr, Charles, and William J. Lamont. 1992.
Schonbeck, Mark. 1995. Mulching choices for
Proﬁts, proﬁts, proﬁts: Three reasons to
warm-season vegetables. The Virginia Bio-
try triple cropping. American Vegetable
logical Farmer. Spring. p. 16–18.
Grower. February. p. 18, 20.
Snyder, Richard L. 2000. Principles of Frost
Mattern, Vicki. 1994. Get your earliest toma-
Protection. University of California. 13 p.
toes ever. Organic Gardening. November.
http://bionet.ucdavis.edu/frostprotection/FP005.
p. 26–28, 30, 32.
htm
Miles, Carol A., and Pat Labine. 1997. Portable
Thompson, James F., Clay R. Brooks, and
Field Hoophouse. Washington State Uni-
Pedro Ilic. 1990. Plastic Tunnel and Mulch
versity Cooperative Extension. 7 p.
Laying Machine. University of California
http://cru.cahe.wsu.edu/
Small Farm Center. Family Farm Series
Publications. 4 p.
// SEASON EXTENSION TECHNIQUES FOR MARKET GARDENERS
PAGE 23

www.sfc.ucdavis.edu
Scheduling Vegetable Plantings for Continuous
Line drawings show key features of plastic tun-
Harvest. ATTRA Publication. 2002. By
nel and mulch laying machine. A list of mate-
Janet Bachmann. NCAT, Fayetteville, AR.
rials needed to construct one in a farm shop is
27 p.
included.
The Hoophouse Handbook: Growing Produce
Upson, Steve. 2004. Hoophouse Construction
and Flowers in Hoophouses and High
Guide. Samuel Roberts Noble Foundation
Tunnels. 2003. By Lynn Byczynski (ed.).
Agricultural Division. 24 p.
Fairplain Publications, Inc. 60 p.
Includes information on construction and man-
Vargo, Adrianna. 2004. 4 ways to use a cold
agement, including crops to grow and sources of
frame. Fine Gardening. November.
supplies. To order, send $15 plus $4 shipping
p. 55–59.
to:

GFM
Wells, Otho. 1992. Want earlier tomatoes? Use

P.O. Box 3747
tunnel vision. American Vegetable Grower.

Lawrence, KS 66046
March p. 38-41.

800-307-8949 (toll-free)
Wiediger, Alison. 2003. Not just season exten-
Extending the Season: Six Strategies for Im-
sion anymore: Hoophouses saved their
proving Cash Flow Year-Round on the
season. Growing for Market. September.
Market Farm. 2004. Edited by Lynn
p. 7.
Byczynski, Fairplain Publications. 60 p.
Includes articles about protected early and late
Zimmerman, John. 2004. Rain-Flo Irrigation
crops; winter crops in the ﬁeld and unheated
catalogue. East Earl, PA.
hoophouse; high-dollar crops for the heated
greenhouse; storage crops to sell months after
harvest; value-added products to sell year-
Further Resources
round; creating year-round markets. $15 plus
$4 shipping from GFM.
Walking to Spring. 2003. By Paul and Alison
Publications
Wiediger. Au Naturel Farm. 94 p.
The Wiedigers tell how they use high tunnels to
Compost Heated Greenhouses. ATTRA Pub-
grow produce 52 weeks a year. Includes infor-
lication. 2001. By Steve Diver. NCAT,
mation on construction, crops grown, record-
Fayetteville, AR. 30 p.
keeping, and additional resources. The price is
$15 plus $3.50 shipping and handling. Order
Greenhouse and Hydroponic Vegetable Re-
from:
sources on the Internet. ATTRA Publica-

Au Naturel Farm
tion. 2000. By Steve Diver. NCAT, Fay-

3298 Fairview Church Road
etteville, AR. 8 p.

Smiths Grove, KY 42171

270-748-4600
Low-cost Passive Solar Greenhouses. 1980. By

wiediger@msn.com
Ron Alward and Andy Shapiro. NCAT,

http://aunaturelfarm.homestead.com/
Butte, MT. 174 p.
High Tunnel Production Manual. 2003. By
Root Zone Heating. ATTRA Publication. 2002.
William J. Lamont et al. The Pennsylvania
By Steve Diver. NCAT, Fayettville, AR.
State University. 164 p.
40 p.
Covers construction, production, and economics
for vegetables, berries, sweet cherries, and ﬂow-
Solar Greenhouse Resource List. ATTRA Pub-
ers. Includes additional resources. To order,
lication. 2003. By Barbara Bellows. NCAT,
send a $25 check made out to The Pennsylvania
Fayetteville, AR. 35 p.
State University to:

Dr. Bill Lamont
Specialty Lettuce and Greens: Organic Produc-

Department of Horticulture
tion. ATTRA Publication. 2002. By George

206 Tyson Building
Kuepper and Janet Bachmann. NCAT,

The Pennsylvania State University
Fayetteville, AR. 26 p.

University Park, PA 16802
PAGE 24
//SEASON EXTENSION TECHNIQUES FOR MARKET GARDENERS

High-Tunnel Tomato Production. 2004. By
The New Organic Grower (Revised edition).
Lewis Jett. University of Missouri Exten-
By Eliot Coleman. 1995. Chelsea Green
sion. 28 p.
Publishing Company. 340 p.
The book covers everything from building high

The New Organic Grower has become a
tunnels to selecting varieties, fertilization,

classic for small-scale market gardening.
caging and staking, pest management, and

This revised edition includes chapters on
intercropping. The intercropping section tells

season extension, including plans for con-
how you can grow 12 different vegetables in a

tructing moveable hoophouses. It provides
12-month period. Available for $10 from:

background information for his 1998 pub-

Extension Publications

lication, below. Eliot Coleman and Barbara

University of Missouri

Damrosch grow and market from October

2800 Maguire Blvd.

through May in Maine.

Columbia, MO 65211

573-882-7216
The Winter-Harvest Manual: Farming the Back

800-292-0969 (toll-free)
Side of the Calendar. 1998. By Eliot Cole-
man. Four Season Farm. 62 p.
Hoop House Construction Guide. 2004. By

This manual describes what Coleman
Steve Upson. Samuel Roberts Noble Foun-

and his wife Barbara Damrosch have
dation Agricultural Division. 46 p.

learned since the above book was written. It
Excellent photos show all construction details

includes their reasons for “farming the
from preparing the site to attaching the poly

back side of the calendar” and details about
covering. The resulting hoophouse is sturdy

how they do it, as well as a list of seed, tool,
enough to withstand the extremes of Oklahoma

and supply companies. Available for $15
weather. Contact:

including postage from:

Steve Upson

Four Season Farm

The Samuel Roberts Noble Foundation,

609 Weir Cove Road

Inc.

Harborside, ME 04642

P.O. Box 2180

Ardmore, OK 73402
Use of Plastic Mulch and Row Covers in Veg-

580-223-5810
etable Production. 2003. By Dean McCraw

sdupson@noble.org
and James E. Motes. Oklahoma Coopera-
tive Extension Fact Sheet F-6034. 8 p.
Four-Season Harvest: Organic Vegetables from
www.osuextra.com
Your Home Garden All Year Long. 1999.
By Eliot Coleman. Chelsea Green Publish-
The Gandhi of greenhouses, Part I & Part II.
ing. 234 p.
2004. By George DeVault. The New Farm.

Inspired by Scott and Helen Nearing’s
April 6, April 20.

garden in the late ‘60s and based on the
www.newfarm.org/features/

author’s success with harvesting fresh
Two articles describe the passive solar produc-

vegetables year-round in New England, this
tion system used by Steve and Carol Moore in

book contains details on design, construc-
Spring Grove, Pennsylvania.

tion, and management of the outdoor gar-

den, cold frames, mobile high tunnels, and
Waste oil heater. 1980. Anon. Mother Earth

root cellars. Also includes growing tips for
News. 11 p.

50 vegetable crops, a planting schedule for
www.bagelhole.org/

extended harvests for all locations in the
The article provides instructions for making

U.S., and sources of tools and supplies.
your own waste oil heater from an old water

Written primarily with the home gardener
heater tank. It is said to burn used crankcase oil

in mind, but much of the material can be
both cleanly and without any detectable odor,

applied to a commercial operation. Avail-
and put out a lot of heat. The heater is designed

able from bookstores, on-line booksellers, or
for use in a shop or garage rather than in an

directly from the publisher:
open ﬁeld.

Chelsea Green Publishing

P.O. Box 428

Gates-Briggs Building #205
Organizations

White River Junction, VT 05001

800-639-4099 (toll-free)
American Society for Plasticulture

www.chelseagreen.com
// SEASON EXTENSION TECHNIQUES FOR MARKET GARDENERS
PAGE 25

526 Brittany Drive

Yakima, WA 98901
State College, PA 16803-1420

509-575-2315
814-238-7045

www.goodfruit.com/buyers/
www.plasticulture.org
A.M. Leonard
National Greenhouse Manufacturers
P.O. Box 816
Association
Piqua, OH 45356

20 W. Dry Creek Circle, Suite 110
800-543-8955 (toll-free)

Littleton, CO 80120
www.amleo.com

800-92-NGMA

General tools, also landscape fabric, plastic

303-798-1338

ﬁlm, shade cloth.

ngma@ngma.com

www.ngma.com/
American Plant Products & Supplies
9200 N.W. 10th
Oklahoma City, OK 73127
Recycling Contacts
405-787-4833
800-522-3376 (toll-free)
American Plastics Council
www.americanplant.com
1300 Wilson Blvd.

Source of greenhouse frames, ﬁlms and
Arlington, VA 22209

glazing, shade cloth, row covers, mulch
800-243-5790 (toll-free)

ﬁlm.
703-741-5000
www.americanplasticscouncil.org/
Atlas Greenhouse Systems, Inc.

Since 1990, the plastics industry, as in-
P.O. Box 558

dividual companies and through organiza-
Alapaha, GA 31622

tions such as APC, has invested more than
800-346-9902 (toll-free)

$1 billion to support increased recycling
service@atlasgreenhouse.com

and educate communities in the United
www.AtlasGreenhouse.com

States. The Association of Postconsumer

Structures. Highly recommended by grow-

Plastic Recyclers hosts a Website as a ser-

ers in the South and Midwest.

vice to the plastic packaging industry to

promote the most efﬁcient use of the na-
CropKing, Inc.

tion’s plastics recycling infrastructure and
5050 Greenwich Rd.

to enhance the quality and quantity of re-
Seville, OH 44273

cycled post-consumer plastics.
330-769-2002
cropking@cropking.com
www.cropking.com
Manufacturers and Suppliers

Offers grower-training workshops in hydro-

ponic production.
NOTE: This list is intended to be neither com-
prehensive nor exclusive. Endorsement of
Dirt Works
any particular product or company is not
6 Dog Team Rd.
implied. Additional suppliers, both whole-
New Haven, VT 05472-4000
sale and retail, are listed in the manuals
800-769-3856 (toll-free)
and on the High Tunnel Web site described
admin@dirtworks.net
above. Many resources are also listed in
www.dirtworks.net/
the American Vegetable Grower magazine’s

Source of Bio-Film 100 biodegradable
annual Source Book (July issue) and the

mulch.
Greenhouse Grower. Contact:

Meister Publishing Co.
FEDCO Seeds

37733 Euclid Ave.
P.O. Box 520A

Willoughby, OH 44094
Waterville, ME 04903

440-942-2000
207-426-9005
www.fedcoseeds.com
Good Fruit Grower is another trade magazine

Floating row covers, plastic ﬁlm mulches.
that lists suppliers. Contact:

Good Fruit Grower
Frost Boss Wind Machine

105 South 18th Street, Suite 217
Hawkes Bay Wind Machines, Ltd.
PAGE 26
//SEASON EXTENSION TECHNIQUES FOR MARKET GARDENERS

Hastings, New Zealand

fastening systems, inﬂation blowers, poly-
www.frostboss.com.nz/

carbonate sheets, and poly patch.

Source of wind machines for frost protec-

tion.
Johnny’s Selected Seeds
955 Benton Ave.
Grifﬁn Greenhouse & Nursery Supplies
Winslow, ME 04901
1619 Main Street
207-861-3900
P.O. Box 36
www.johnnyseeds.com
Tewksbury, MA 01876

Floating row covers, slitted row covers,
978-851-4346

black poly mulch, IRT-100 green poly
www.grifﬁns.com

mulch, landscape fabric, tacks and staples,

Wholesale distributor of a range of plasti-

cold frames, seeds for hoophouse/greenhouse

culture products.

production and for hot weather lettuces.
Harmony Farm Supply & Nursery
KEN-BAR, Inc.
3244 Hwy. 116 North
25 Walkers Brook Drive
Sebastopol, CA 95472
Reading, MA 01867-0704
707-823-9125
800-336-8882 (toll-free)
info@harmonyfarm.com
info@ken-bar.com
www.harmonyfarm.com
www.ken-bar.com

Floating row covers, frost blankets, land-

Suppliers of Dupont AG-06, Typar, Cus-

scape fabric, cold frames, greenhouse poly.

tom-Cover 5131, clear polyethylene slitted

and punched row covers, Insolar slitted/
Haygrove Tunnels

punched row covers or tunnels, wire for
Ralph Cramer

hoops, embossed and smooth black plastic
116 Trail Road North

mulch, Planters Paper mulch, SRM-Red
Elizabethtown, PA 17022

plastic mulch, IRT plastic mulch, and clear
866-HAYGROVE (toll-free)

polyethylene tubes.
Ralph.cramer@haygrove.com
www.haygrove.co.uk
Ledgewood Farm Greenhouse Frames
Route 171
Holland Transplanter Co.
Moultonboro, NH 03254
P.O. Box 1527
603-476-8829
Holland, MI 49422-1527

Manufacturere of Penn State type Gothic-
800-275-4482 (toll-free)

arch design frames.
www.transplanter.com

Manufacturer of mechanical transplanters,
Mechanical Transplanter Co.

bed shapers, mulch layers, mulch lifters,
1150 Central Ave.

and related equipment.
Holland, MI 49423
800-757-5268 (toll-free)
Hummert International
mtc@mechanicaltransplanter.com
4500 Earth City Expressway
www.mechanicaltransplanter.com
Earth City, MO 63045

Mechanical transplanters, bed shapers,
800-325-3055 (toll-free)

mulch layers, mulch lifters, low tunnel lay-
www.hummert.com

ers, ﬂoating row covers, colored ﬁlm mulch-

Drip irrigation, landscape fabric, green-

es, and photodegradable mulch.

house frames, poly covering, ﬂoating row

cover, other supplies.
Orchard-Rite, Ltd.
P.O. Box 9308
Jaderloon
Yakima, WA 98909
P.O. Box 685
509-457-9196
Irmo, SC 29063
www.orchard-rite.com
800-258-7171 (toll-free)

Source of wind machines and orchard heat-
jaderloon@jaderloon.com

ers.
www.jaderloon.com

Offers a complete line of structures and
Peaceful Valley Farm Supply

wide selection of accessories including ﬁlm
P.O. Box 2209
// SEASON EXTENSION TECHNIQUES FOR MARKET GARDENERS
PAGE 27

Grass Valley, CA 95945
888-439-6121 (toll-free)
888-784-1722 (toll-free)
www.repelgro.com
www.groworganic.com

Metalized UV reﬂective and other plastic

Agribon and Tufbel ﬂoating row covers,

ﬁlm mulches.

slitted row covers, shade cloth, IRT mulch,

Planters Paper, black embossed polyethylene
Stuppy Greenhouse Mfg.

mulch ﬁlm, repair tape, clips, hoops, Wal -
1212 Clay
O’-Water.
North Kansas City, MO 64116
800-733-5025 (toll-free)
Plastitech, Inc.
greenhouse@stuppy.com
478 Notre Dame
www.stuppy.com
St. Remi, Quebec

Offers a variety of both coldframes and
Canada J0L 2L0

greenhouses.
450-454-3961
800-667-6279 (toll-free)
Special thanks for their contributions to Dr. Wil-
info@plastitech.com
liam J. Lamont, Dr. Carol Miles, Lynn Byczynski
www.plastitech.com
and Dan Nagengast, Alison and Paul Wiediger,

Plastic mulch, ﬂoating row covers, tunnels,
Ralph Cramer, Steve Groff, Alex Hitt, Bryan

irrigation, artiﬁcial windbreak material,
Boeckmann, and Steve Upson.

mechanical mulch layers.
Rain-Flo Irrigation
884 Center Church Rd.
East Earl, PA 17519
717-445-6976

On-farm family-owned and -operated busi-

ness. Manufactures vegetable growing ma-

chinery and supplies and carries almost all

brands of irrigation equipment, specializing

in drip irrigation. Floating row covers,

plastic ﬁlm mulches, mulch layers, trans-

planters, mulch lifters.
ReﬂecTek Foils, Inc.
P.O. Box 310
Lake Zurich, IL 60047
PAGE 28
//SEASON EXTENSION TECHNIQUES FOR MARKET GARDENERS

EB1825 Portable Field Hoophouse
APPENDIX I. Season Extension Techniques for Market Gardeners: Portable Field Hoophouse
EB1825
By
Carol A. Miles, Ph.D.,
Washington State University Cooperative Extension
Area Agricultural Systems Agent, Lewis County
Pat Labine, Ph.D.,
The Evergreen State College, Olympia, WA
When constructing a greenhouse would be unwieldy and too expensive, a plastic-enclosed
house—the hoophouse—fulfills most of a small farmer's or home gardener's needs. So named
because of the arched or "hoop" structure that supports the plastic "skin," hoophouses are
available in many lengths.
If you have a small farm business and are looking for ways to increase crop diversity or
earliness, this portable field hoophouse may help. Some crops that are well suited to this type of
hoophouse include tomatoes, peppers, eggplants, and melons—crops that need to be planted after
danger of frost and that generally mature late in the season west of the Cascade Mountains. The
hoophouse effectively allows a grower to produce early yields of crops that require more heat
units than the environment may otherwise provide.
The hoophouse rests directly over the soil in the field, using no benches or special growing
media. Two people can easily dismantle and reassemble the lightweight structure in a different
section of the field each year or within a growing season. An advantage to moving the hoophouse
around the field is crop rotation, which avoids pest buildup. Another is the low cost,
approximately $350 for a 10' X 42' hoophouse.
The following hoophouse design will result in a structure approximately 10' wide at the base, 6
1/2' high at the center, and 42' long (Figure 1). Growers can easily adjust the length by adding or
taking away support hoops and altering the length of the polyethylene plastic appropriately. The
maximum length of polyethylene plastic available on the market is 100', which governs the
maximum length for constructing a hoophouse. While initial construction of the hoophouse will
take a day, two people can later put it up and take it down in only 2 hours. Storing the hoophouse
out of the field during the winter months spares it from some of the worst weather and makes it
last many years. Using wood treated with water- based preservatives also increases the longevity
of the structure.
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EB1825 Portable Field Hoophouse
FIGURE 1.

Portable field hoophouse, 10' wide by 42' long, resting directly

on soil surface in the field.

Selecting Materials
Polyethylene plastic is available in many grades. A 6 mil weight is recommended for
greenhouses. Selecting a lighter weight (4 mil) is not recommended. Untreated polyethylene will
cost less initially; however, the lifespan of the material is significantly less, and the material will
likely degrade after one year of use. When treated with a UV inhibitor, 6 mil plastic generally is
guaranteed for 3 years.
Gases that escape from the PVC (polyvinyl chloride) pipes contribute to the deterioration of the
polyethylene plastic. To prevent "off-gasing," paint the PVC pipes with white latex paint. Use
wood treated with water-based preservatives for the base of the door frame, where the wood
comes into contact with the soil. Untreated wood used for the remainder of the frame will not
severely affect its longevity. Choose a mid-weight (4 oz to 5 oz) corrugated plastic for the ends.
A clear plastic generally will darken over the years, whereas a colored plastic will lighten with
time. The color of the plastic will not affect the usability of the hoophouse. Most light will enter
through the polyethylene sides.
The choice of nylon twine for tying the hoops in place is broad. Twisted twine is susceptible to
unraveling, while braided twine is more durable. Natural fiber twine (jute or cotton) is not
recommended due to the stretching these materials experience. Baling twine is inexpensive and
durable.

Materials

q 9 ea. 2" X 4" X 12' boards, treated with water-based
preservatives
q 4 ea. 2' X 8' sheets of 4 oz greenhouse-grade corrugated
plastic
q 30 ea. 1/2" X 18" lengths of reinforcing rod (rebar)
q 17 ea. 18' lengths of 1" rigid white schedule 40 PVC (20'
lengths cut down)
q 430' good quality nylon twine (minimum tensile strength 210
lbs.)
q 1 piece of 6mil polyethylene plastic sheeting, 50' long x 20'
wide
q 38 ea. 3" galvanized self-tapping screws with rubber washers
q 30 ea. 1" galvanized self-tapping screws with rubber washers
q 10 ea. 1/4" X 4" bolts and matching wing nuts
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EB1825 Portable Field Hoophouse
q battery powered drill
Building the Ends

Two of the two-by-four boards will become the bottoms of the door frames. Construct both door
ends in the same fashion. For each door frame, place an 11-foot length of two-by-four down with
a 4-inch side facing up. Mark the center of the 11-foot board, then mark 14 1/2" on each side of
the center. These marks frame a 29" length in the middle of the board, which will become the
bottom of the doorway. At each end of the framing board, measure 6" and drill two 1-inch holes
next to each other into the bottom piece, placing the holes as close together as possible (Figure 2).

FIGURE 2.

Top view of bottom piece with two holes drilled 6" from each end and door uprights marked, and
front view of the hoophouse end frame.

Turn the bottom piece on its side and insert a PVC length into holes at opposite ends, to form a
hoop. This will be the outermost hoop. The corrugated plastic and door frame will attach to it.
Cut two 6-foot lengths of two-by-four for the door uprights, along with one 32-inch piece for the
top (header) of the door. Screw the header into the uprights, using the 3-inch self-tapping screws,
so that the door frame is 2" wide and 4" deep. The door frame is then screwed to the bottom
piece at the marked position using 3-inch self-tapping screws. Brace each side of the doorway
with a two-by-four cut 72" long with the ends appropriately angled. Screw braces in place with 3-
inch self-tapping screws.
Cut the corrugated plastic, lining up the ridges horizontally, to fit the ends of the hoophouse.
Fitting the corrugated plastic horizontally gives added strength to the ends. Overlap the top piece
of corrugated plastic a few inches over the bottom piece to keep the ends weatherproof. Use 1-
inch self-tapping screws with rubber washers to attach the corrugated plastic to the door frame
and the hoop. The rubber washer is helpful to keep the corrugated plastic from cracking.
Attaching the ends to the hoop structure with bolts makes the hoophouse quite easy to take apart
and reassemble.

Forming the Hoop Structure

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EB1825 Portable Field Hoophouse
In the field, mark an area 10' wide by 42' long for the hoophouse site. At each of the four corners
iques for Market Gardeners: Portable Field Hoophouse
hammer an 18-inch piece of reinforcing bar (rebar) 12" into the ground, leaving 6" above the
surface. The aboveground portion of the rebar will hold the PVC hoops of the hoophouse in
place. Place a door frame upright at one end, inserting the PVC hoop onto the rebar. In what will
be the inside of the hoophouse, attach a support leg to each door upright (Figure 3). Using 3-inch
self-tapping screws, attach the support legs to the side of each door frame that will face the
polyethylene plastic. Attach a support "foot" to the end of each leg and pound them into the
ground. The support legs will keep the hoophouse frame from shifting, losing its shape, or
straining the plastic. Place the second door frame at the opposite end of the area marked for the
hoophouse. Insert the PVC hoop over the rebar and secure with support legs in the same fashion.
FIGURE 3.
Support leg and "foot," attached to the side of door upright which will face the polyethylene
plastic, on what will be the inside of the hoophouse.
At 3-foot intervals along each of the 42-foot sides, hammer rebar into the ground, always leaving
6" above the surface. Gently bend an 18-foot length of PVC, positioning each end directly above
the rebar, and carefully slide the PVC ends onto the rebar to form an arch (Figure 4). Repeat this
procedure until you have formed 13 PVC hoops. It is not necessary to insert rebar into the two
remaining holes in the bottom of each of the door frames. Simply insert the PVC into the holes,
forming a double hoop at each end. When the polyethylene plastic is in place, bolt the double
hoops together.

FIGURE 4.

View of the PVC hoops outlining the sides of the hoophouse.
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EB1825 Portable Field Hoophouse
Starting at one end of the hoophouse, attach one end of the twine to the top center of the second
hoop—the hoop immediately next to the door frame end. Pass the twine over to the next hoop,
pulling it tight and looping it around the hoop. Continue on to each successive hoop until all
hoops are attached together. When you reach the last hoop, reverse the process until you are back
where you started. Connecting the hoops with twine helps to stabilize the hoop frame and will
support the polyethylene plastic that will lie on top of it. It is important to keep the twine tight to
prevent the plastic from sagging and collecting water when it rains. This would cause stress on
the plastic and on the PVC framework.
Measure and cut a 5-foot strip off the 50-foot length of polyethylene plastic. This will leave a
piece 45' long by 20' wide to be used for the hoophouse body. Use the piece 5' long by 20' wide
for the doors. Spread the 45-foot length of polyethylene plastic across the hoop structure, pulling
it tight, and insert the ends of the plastic between the double-hoops at each end. Bolt the
corrugated plastic to the double-hoop ends, keeping the polyethylene plastic sandwiched
between. To bolt the ends together, drill five holes through the corrugated plastic, the double-
hoop ends, and the polyethylene plastic. Space the bolts so that one is at the top center, and two
are on each side spaced 2' apart (Figure 2). Place a rubber washer over the hole on the corrugated
plastic side, insert the bolt, and secure the wing nut on the inside of the hoophouse.
Secure the polyethylene plastic in place with twine tied over every hoop except the double hoop
ends. To attach the twine to the hoops, lift the PVC hoop up slightly, tie a 20-foot length of twine
to the rebar, and slip the PVC hoop back in place. Throw the twine over the hoophouse to the
other side and tie it in the same fashion to the rebar supporting the other end of the PVC hoop.
The twine should be just loose enough to allow slipping the polyethylene plastic up when raising
the sides of the hoophouse for ventilation. Tying the plastic down at each hoop prevents the
plastic from blowing out due to wind pressure.
Finishing Touches

The doors are simply polyethylene plastic sheeting, weighted on the bottom and hung on hooks
at the top of the doorways. Cut the remaining piece of 5' X 20' polyethylene plastic to form two
pieces 5' wide and 6' long. Attach a narrow piece of scrap wood at each end of the 6-foot length
of polyethylene plastic. You can roll the plastic doors up on warm days to allow a breeze through
the hoophouse, lowering the temperature. The polyethylene plastic along the 42-foot sides of the
hoophouse also can be rolled up and attached with twine to the hoops (Figure 5). This additional
ventilation is necessary during the hot summer months in most climates. To use the hoophouse,
form two soil beds, one running down each side of the hoophouse, and install drip tape in each
bed for easy watering (Figure 6). Transplant or direct seed crops into the soil.
FIGURE 5

View of the side of the hoophouse, showing polyethylene plastic

secured by twine. A side of the hoophouse has been raised for
ventilation and tied in place with twine.
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EB1825 Portable Field Hoophouse

FIGURE 6.

Transplant crops into the soil inside the hoophouse. Lay drip

tape down the center of each bed.

Issued by Washington State University Cooperative Extension and the U.S. Department of
Agriculture in furtherance of the Acts of May 8 and June 30, 1914. Cooperative Extension
programs and policies are consistent with federal and state laws and regulations on
nondiscrimination regarding race, color, gender, national origin, religion, age, disability, and
sexual orientation. Evidence of noncompliance may be reported through your local Cooperative
Extension office. Trade names have been used to simplify information; no endorsement is
intended. Published January 1997. Subject code 330 B
EB1825
Order a print copy
Top
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APPENDIX II. Season Extension Techniques for Market Gardeners: Design and Construction of the Penn State High Tunnel
Design and
tural production. The HTREF con-
tillage and other operations associated
sists of 28 high tunnel research units
with plasticulture systems and 2) to
Construction of
that have dimensions of 17 ft wide × 36
allow separate sheets of plastic to be
ft long × 9 ft high (5.2 × 11 × 2.7 m)
used for the covering the top and sides
the Penn State
and a support building located at the
of the high tunnel that would facilitate
Horticulture Research Farm, Russell
a quicker means of recovering a tunnel
High Tunnel
E. Larson Research Center, Rock
if a problem developed with either the
Springs, Pa. Here research is being
plastic covering on the top or sidewalls.
conducted to evaluate new designs for
William J. Lamont, Jr.,1
high tunnels and plastic coverings,
Details of construction
cropping options, sequencing of veg-
using the Penn State high-
Martin R. McGann,2
etables and other horticultural crops,
tunnel design
Michael D. Orzolek,3
as well as production recommenda-
tions and budgets for crops grown in
The pipe framing and assembly is
Nymbura Mbugua,4
high tunnels.
the same for either the New Hampshire
or the Penn State design. A general view
Bruce Dye,5 and
The first eight tunnels were con-
structed using the design and system
of the Penn State high tunnel is pre-
Dayton Reese6
of crop production developed by Otho
sented in Fig. 2. A detailed list of com-
Wells and colleagues from the Univer-
ponents and prices used in construction
sity of New Hampshire (Sciabarrasi and
of a 17 × 36-ft high tunnel using the
ADDITIONAL INDEX WORDS. season extend-
Wells, 1999; Wells, 1991,
Penn State design can be found in the
ing technology, plasticulture, plastic
1996, 2000; Wells and Loy,
mulch, drip irrigation, fertigation
1993). The New Hamp-
shire design (Fig. 1) con-
SUMMARY. Plasticulture technology,
sisted of wood-framed end
especially high tunnels for extending
the production period of a wide variety
walls that were covered ei-
of horticultural crops, is an accepted
ther with clear plastic film
production practice worldwide. In
or exterior grade plywood.
particular, high tunnels offer a
A door was framed into the
production system that minimizes the
end wall for general access
effect of the environment on crop
in and out of the tunnel. To
production and allows growers to
accomplish tillage opera-
continue to farm in densely populated
tions in the tunnel, the end
areas. Only recently has the use of high
walls had to be removed.
tunnels in the U.S. been investigated
This required detaching the
and this research has been centered in
the northeastern U.S. In 1999 the
plastic and removing a se-
High Tunnel Research and Education
ries of screws. In addition, a
Fig. 1. High tunnel constructed
Facility was established at Pennsylvania
continuous sheet of 4-year, greenhouse
using the New Hampshire design
State University that resulted in the
grade, clear plastic film was used to
developed by Otho Wells, University
development of a unique high tunnel
cover the entire tunnel, both the top
of New Hampshire.
design. A detailed description of the
and roll-up sides. The plastic was at-
new design and construction is
tached to a 1 × 6-inch (2.5
presented in this report.
× 15.2-cm) hipboard, us-
ing two 1 × 3-inch (2.5 ×
The High Tunnel Research 7.6-cm) boards that were
and
Education
Facility
attached to the hipboard.
(HTREF) was established at
If a problem developed
the Pennsylvania State University as
with the top covering or the
part of the Penn State Center for Plas-
roll-up sidewalls, or the cov-
ticulture. The center is a clearinghouse
ering needed to be replaced,
for research and educational efforts in
all the screws fastening the
the field of plasticulture, which is the
1 × 3-inch board had to be
use of plastics in any phase of agricul-
removed. This caused prob-
lems with the integrity of
Department of Horticulture, Pennsylvannis State Uni-
the screws and weathering
versity, University Park, PA 16802.
of the boards due to a
1Associate professor of vegetale crops.
buildup of moisture under
2Assistant professor of landscape contracting
the plastic.
Fig. 2. High tunnel constructed
3Professor of vegetable crops.
The objectives for developing a
using the Penn State design devel-
4Postdoctoral at the High Tunnel Research and Edu-
new high tunnel design were 1) to
oped by researchers and extension
cation Center.
developed end walls that would afford
specialists at the Penn State High
5Research support associate.
quicker and more convenient access
Tunnel Research and Education
6Construction technician.
into the tunnels for performance of
Facility.
G July–September 2002 12(3)
447

TECHNOLOGY & PRODUCT REPORTS
Fig. 4. Connection of the hip board to the steel bow. (A) Galva-
nized pan-head self-tapping set screw to keep the hip board in
alignment on the bow. (B) Two-hole, standard-duty galvanized
1.25-inch (3.2-cm) pipe-strap hanger. (C) Two 1.25 × 0.375-inch
Fig. 3. Installation of the ground post and
(3.2 × 1.0-cm) galvanized steel carriage bolts, nuts, and washers
baseboard. (A) Hollow galvanized-steel bow. (B)
to connect the strap hanger to the hip board. (D) Hollow galva-
Two pressure-treated wooden baseboards
nized steel bow. (E) A 1.0 × 4.0-inch (10.2 × 2.54-cm) pressure-
(reference Fig. 15G). (C) One 4.5 × 0.25-inch
treated wooden hip board. (F) Hip boards are cut flush with the
(11.4 × 0.6-cm) galvanized carriage bolt installed
bows at the north and south ends of the greenhouse. A one-hole,
through pre-drilled holes in the ground post and
standard-duty 1.25-inch galvanized pipe strap is used to connect
bow. Materials are lined up with pre-drilled
the hip board to the bow.
holes in the bow and ground post as supplied by
the manufacturer before insertion of the bolt.
(D) Galvanized eye screw for use in connection
of the Arbor-Tie line. (E) One 4.5 × 0.25-inch
galvanized carriage bolt installed through pre-
drilled holes in the ground post and the base-
board. Pre-drilled holes supplied by the manu-
facturer are the only holes used when attaching
the baseboards. (F) The manufacturer-supplied
ground post should be installed to a recom-
mended minimum depth of 20 inches (50.8 cm)
below finished grade. There should be a mini-
mum of 12 inches (30.5 cm) and a maximum of
16 inches (40.7 cm) remaining above finished
grade for installation of the bow and baseboard.
(G) Ground level or finished grade.
Penn State High Tunnel Manual
(Lamont et al., 2001) available from the
senior author. The manual also includes
extensive environmental data as well as
information on production of a wide
Fig. 5. Installation of the double-rail
variety of horticultural crops in the high
ground posts are 13-gauge pipe with a
track to the hip board. (A) Surelock
tunnels. The price for the 17 × 36-ft
1.9-inch (4.83-cm) outside diameter
aluminum double-rail track. (B)
high tunnel is about $1,900.00, de-
(OD), the bows are 14-gauge pipe with
Surelock preformed aluminum cap.
pending on prices of locally purchased
a 1.66-inch (4.2-cm) OD and the pur-
(C) Plastic covering placed between
materials.
lins and roll-up pipes are 15-gauge pipe
the track and clamp. (D) A no. 10 ×
1-inch (2.5-cm) galvanized hex-head
with 1.32-inch (3.25-cm) OD. It is
Construction steps
wood screws are used every 2 ft (0.6
recommended that high tunnel kits with
m), on center, to hold the rail to the
The pipe frame kits were purchased
extended sides be purchased that allow
hip board. (E) Hip board. (F) Plastic
from Ledgewood Farms (Moultonboro,
the hipboard to be positioned higher on
covering of the greenhouse trimmed
N.H.). The high tunnel pipe frame kit
the bows and the roll-up sides to be raised
so that a flap, even with the lower
(17 × 36 ft) consisted of ground posts,
higher for more efficient ventilation.
edge of the hip board, remains. (G)
bows, purlins, roll-up sides kit, and nuts
The ground posts are driven into
Plastic for the side panel roll-up wall
and bolts. The pipes used in the kit are
the ground to a minimum depth of 20
locked in place with the lower clamp
made of galvanized steel tubing. The
inches (50.8 cm), and allowing suffi-
on the double aluminum track.
G July–September 2002 12(3)
448

the bow and attach the hipboard with a
3 3/8-inch (8.6-cm) bolt.
STEP 3. Using screws, attach 3.25-
inch (9.5-cm) Surelock aluminum
double rail track (Keeler-Glasgow Com-
pany, Hartford, Mich.) to the hipboard
for securing the plastic cover and plastic
for the sides (Fig. 5 and Fig. 6).
STEP 4. Construct the upper
endwalls with a bracing and a vertical
board (Figs. 7, 8, and 9). Use a 2 × 4-
inch × 12-ft (5 × 10.2-cm × 3.6-m)
board and taper the ends so that it will
fit securely between the end bows as a
bracing board, temporarily attaching it
to the end bow to facilitate measure-
ment of the vertical board. Take an-
other 2 × 4-inch board (flat side out)
and place it in the center of the bracing
board. Measure and cut the vertical
board so that it fits snug between the
bracing board and center ridgepole pur-
lin. This will require that the vertical
Fig. 6. Surelock aluminum double-rail track attached to the hipboard used to
board be notched to fit around the
attach the plastic covering to the top and side of the high tunnel. Clip is being
center ridgepole purlin. Secure the ver-
fastened to the lower track.
tical board to bracing board with mend-
ing plates front and back (Fig. 10A, B,
and D). Place this frame (bracing and
vertical board) in place and drill a hole
on an angle up through the ends of the
bracing board into the metal bow, se-
curing it with a large self-tapping metal
screw (Fig. 11E). Next take galvanized
pipe strap and bring it over the top of the
end bow and down to the bracing
board using pan-head wood screws to
secure the strapping tightly on both
sides of the board (Fig. 11D). Next,
take the galvanized pipe strap over the
end bow and secure it to both sides of
the vertical board, using pan-head wood
screws (Fig. 12). The triangle section at
the top of the endwalls can be covered
with a variety of materials but in the
Fig. 7. The interior view of the front section or south end of the high tunnel.
Penn State design reported here it is
covered with 3/8-inch (0.95-cm) exte-
cient length above the ground for at-
30.5-cm × 3.65-m) boards. A single 2 ×
rior plywood (Figs. 7 and 8).
tachment of the baseboard. Ground
12-inch
STEP 5.
× 12-ft board eliminates the
Attach the aluminum
posts are placed on 4-ft (1.2-m) centers.
potential gap that may occur when two
single-track nursery lock (Keeler-
The bows are then assembled and the
2 × 6-inch boards are used for the
Glasgow Co.) over the end bows down
ends inserted into the ground post and
baseboard. The boards should meet at a
to the hipboards (Fig. 12E). This is best
secured using the appropriate hardware.
bow and are attached using a carriage
accomplished by two people, one per-
The purlins (ridgepole and two side
bolt with a large 5/16-inch (0.79-cm)
son holding the track on the bow while
purlins) are then assembled and attached
washer that overlaps both boards.
the second person drills holes through
to the bows. The corner braces are
STEP 2. Attach the hipboard. The
the track and the bow and fastens the
attached to keep the tunnel from shift-
hipboard is a pressure-treated 1 × 4-inch
track to the bow using self-taping screws.
ing out of upright position. The addi-
(2.5
STEP 6.
× 10.2-cm) board that is held in
The next step is to build
tional construction steps after the erection
place with a 1.25-inch (3.2-cm) pipe
the lower end walls. The Penn State
of the pipe frame are described below.
strap hanger (Fig. 4). Secure the pipe
design allows for the center section of
STEP 1. Attach the baseboards
strap hanger to the bow with a small
the end walls to be lifted up (Fig. 13)
(Fig. 3). The baseboards are pressure-
sheet metal screw to prevent the strap
to accommodate the accessibility of a
treated 2 × 6-inch × 12-ft (5 × 15.2-cm
from moving up the bow in high winds.
small four-wheel-drive, 21-horsepower
× 3.65-m) or 2 × 12-inch × 12-ft (5 ×
The other option is to drill a hole through
tractor with equipment. Equipment
G July–September 2002 12(3)
449

TECHNOLOGY & PRODUCT REPORTS
STEP 7. On either side of the
center section are two hinged end pan-
els (Figs. 14 and 15). These are con-
structed of 2 × 4-inch lumber frames
that have a pressure-treated base piece
and are attached to the side bows by
heavy metal pallet strapping. They can
be covered with a variety of materials. In
the original stages of development alu-
minum-covered Styrofoam insulating
material was used but now 3/8-inch
exterior plywood is being used. Whatever
material is chosen, it is cut to the outline of
the bow and overlaps the edge of the
center section (Fig. 14). It is held against
the edge of the center section by a small
piece of wood that rotates on the inside
of the end panel (Fig. 15J).
STEP 8. The next step is to cover
the top of the high tunnel. The plastic
Fig. 8. The exterior view of the front section or south end of the high tunnel.
used for covering the high tunnels is 3-
or 4-year life, greenhouse-grade 6-mil
[0.006-inch (144-µm)] plastic. It helps
to have a crew of six people and a day
with wind less than 5 miles/h (8.0
km·h–1) to facilitate covering the tun-
nel. Snap-on clips attach the top piece
of plastic to the single aluminum rail
on the end bows. The top track of the
double aluminum track attached to
the hipboard makes the covering or
recovering of the tunnels easier than
the New Hampshire design. The roll-
up sidepieces of plastic are 6.5-ft (2.0-
m) wide and are clipped into place on
the lower track of the double track
(Fig. 5B). The lower end of the roll-up
side is then attached to the roll-up pipe
by plastic clips at every bow, while the
pipe is lying on the ground. Trim
Fig. 9. The exterior view of the rear section or north end of the high tunnel.
excess plastic [suggest 8-inch (20.3-
cm) overhang] for sidewalls (Fig. 5).
includes a three-point hitch-mounted
mended to attach the plastic on the end
The plastic can then be rolled up on the
rototiller, that is used to prepare the
walls using batten tape and staples while
pipe (Fig. 16). Where the sections of
soil and a small plastic mulch–drip
they are flat on the ground. The end
roll-up pipe slide in to one another it is
irrigation tape applicator that is used
walls are attached to the overhead brac-
recommended to put two small ma-
to make raised plastic-mulch-covered
ing board with three strong 3.5-inch
chine screws, one on each side, so the
beds with drip irrigation. The dimen-
(8.9-cm) galvanized gate hinges (Figs.
pipes cannot rotate.
sions of the center section of lower end
8 and 9). Details of the service door are
STEP 9. The next step is to attach
walls are 12 ft wide by 8 ft high (3.6 ×
presented in Fig. 10. In a commercial
four eyescrews on upper portion of the
2.4 m). The exterior frame of both
size high tunnel [17 × 96 ft (5 × 29 m)]
baseboard; one at each end and two
sections is constructed of 2 × 4-inch
that a grower would purchase there
spaced equally apart between the ends
lumber with all bottom boards pres-
would be a service door at each end. The
(Fig. 3D). AborTie, a soft polypropy-
sure treated because of contact with
center section of the lower endwall
lene material, (Ben Meadows Com-
soil and water. On the 17 × 36-ft
should be securely fastened when in the
pany, Janesville, Wis.) is placed over the
research units there is an entrance door
open position. The authors use 2 × 2-
tunnel and attach at the eight eyescrews.
framed on the south end wall (Fig. 8).
inch posts with metal dowels at each
This will prevent the top cover and sides
The north end wall uses 2 × 2-inch (5-
end. One end of the post is placed in the
from flapping in the wind.
cm) lumber for internal support (Fig.
soil and the upper dowel is placed
STEP 10. Each tunnel will need its
9). All the wood for the end walls is
through a pre-drilled hole in the door
own water supply and fertilizer injection
secured using mending plates on both
stop (Fig. 8). The upper metal dowel
unit. Any piping to service the units
sides. The end walls are best assembled
should extend above the doorstop by
should be in a location where tilling
on a firm, flat surface. It is recom-
several inches.
operations will not damage the lines.
G July–September 2002 12(3)
450

There are different options on con-
tunnel for water to fill the stock fertilizer
Conclusions
structing a fertilizer injection system
containers (Fig. 17). This allows for the
The Penn State high tunnel de-
(fertigation) and water supply system to
precise watering of crops using drip
sign demonstrates that the improve-
the tunnels. The one used in the Penn
irrigation and the ability to add addi-
ments described allow for greater ease
State High Tunnels consists of an 11-
tional fertilizer as needed to crops espe-
of access for equipment operations and
gal/min (41.6-L·min–1) Dosatron
cially, in double cropping situations on
periodic replacement of plastic than pre-
(Dosatron International, Clearwater,
plastic mulch.
viously designed systems.
Fla.) unit for fertigation, a preset pres-
The Penn State high tunnel design
sure regulator and a screen filter. It is
of the end walls allows easy access for
convenient to have a spigot in each
small power tillage equipment to the
inside of the high tunnel for preparation
of the soil and other operations associ-
ated with the use of plasticulture. It is a
very quick operation to open the hinged
end panels and lift up the center section
of the end walls.
The change made to the way the
plastic is attached to the hipboard allows
for easy removal of either the plastic
covering the top or the side walls, if a
problem develops, or the covering needs
to be changed due to age or a grower
wishes to use different covering or ma-
Fig. 11. Connection of the upper end
terials such as insect screen on the side
wall to the end bow. (A) Hollow
walls. The aluminum track system with
galvanized steel end bow. (B) A 2 × 4-
clips is more convenient to work with
inch × 12-ft (5 × 10.2-cm × 3.6-m)
bracing board of finished lumber is
used as a fixed support for the flip-up
end panel. Both ends taper cut so that
the board will fit snugly against the
bow and parallel to the ground.
Bottom dimension on the board
should be 12 ft (3.6 m). (C) A 3.5-
inch (8.9-cm) galvanized gate hinge
Fig. 10 Construction of the main
installed on bracing board and upper
entrance door. (A) A 2 × 4-inch (5 ×
support for flip-up end panel. (D)
10.2-cm) vertical support from the
Steel pipe hanger strapping used to
bow to the bracing board. (B) A 3 ×
secure the wooden support to the end
5-inch (7.6 × 12.7-cm) galvanized
bow. Galvanized pan-head wood
mending plate, both front and back.
screws with washers used to secure the
(C) A 3.5-inch (8.9-cm) galvanized
strap to the wood. (E) Wooden
Fig. 12. Attachment of the upper
gate hinge installed on the bracing
support is also attached to the bow
end-panel wall to the center ridge
board and upper support for the flip-
with a self-tapping sheet-metal screw
pole purlin/end bow. (A) Hollow
up door. (D) A 2 × 4-inch × 12-ft (5 ×
countersunk 0.5 inches (1.3 cm)
galvanized steel end bow. (B) Center
10.2-cm × 3.6-m) bracing board. (E)
below the surface of the wooden
ridge pole purlin attached to bow
2 × 4-inch × 12-ft upper support for
support. Screw hole is located no
with hardware kit supplied by
flip-up door. (F) A 3 × 5-inch
closer than 2.5 inches (6.4 cm) to
manufacturer. (C) Single-track
galvanized mending plate located at
either end of the board. (F) Upper
aluminum nursery lock channel
top and bottom of vertical door
support of 2 × 4-inch × 12-ft finished
mounted on the crest of the bow with
supports, both front and back. (G) A
lumber. (G) A 3 × 5-inch (7.6 × 12.7-
sheet-metal screws. (D) Galvanized
2 × 4 × 77-inch (5 × 10.2 × 195.6-cm)
cm) galvanized mending plates used
pipe strap used to attach the vertical
vertical door support. (H) A 2 × 2-
front and back to secure corners of
support to the end bow with no. 8 ×
inch (5-cm) door framing. (I) A 2 ×
panel. (H) Panel stop constructed of 1
1.25-inch (3.2-cm) galvanized pan-
2-inch cross support for door frame.
× 4 × 7-inch (2.5 × 10.2 × 17.8-cm)
head screws and washers. One strap
(J) A 2 × 3-inch (5 × 7.6-cm) galva-
finished lumber and attached to the
mounted on each side of the center
nized entrance door hinge, three per
inside of the panel with 4 #8 × 2.5-
purlin and fastened both front and
door equally spaced. (K) A 2 × 4-inch
inch (6.3-cm) flat-head galvanized
back Straps installed before the lock
galvanized mending plate located at
wood screws. Two stops, one top and
channel. (E) A 2 × 4-inch (5 × 10.2-
each doorframe corner, both front
one bottom, mounted on each side of
cm) vertical support for the lower
and back. (L) A 2 × 4-inch × 12-ft
the panel. (I) A 2 × 4 × 77-inch (5 ×
bracing board. The center of the
lower support for flip-up door,
10.2 × 195-cm) side support made of
board is custom cut to accommodate
pressure-treated lumber. (M)
finished lumber for flip-up panel. (J)
the ridge purlin before installation.
Suggested dimension 28 inches (71.1
A 2 × 4-inch (5 × 10.2-cm) side
The upper end of the board should
cm). (N) Suggested dimension 77
support of finished lumber for the
rest snugly against the under side of
inches (195.6 cm).
hinged side panel.
the bow.
G July–September 2002 12(3)
451

TECHNOLOGY & PRODUCT REPORTS
Fig. 13. Center section of lower portion of the end
walls used in the Penn State high tunnel design
opened up to allow easy entrance and exit of
machinery.
Fig. 15. Detail of the hinged end
panel as seen from the interior of the
high tunnel. (A) A 0.375-inch (1-cm)
exterior-grade plywood panel cut to
the curvature of the bow and then
attached to the panel frame. (B) A 2
× 2-inch (5-cm) wooden bracing
attached to the panel frame with
galvanized wood screws. (C) Galva-
Fig. 14. Side panel opened up before raising the
nized steel end bow with single track
center section in the Penn State high tunnel
aluminum nursery lock channel. The
design.
nursery lock channel is mounted on
the crest of the bow with sheet metal
screws. (D) Pressure treated 1
and offers a more permanent system
× 4-
inch (2.5 × 10.2-cm) wooden hip
unlike the wood attachment system that
board with double rail track (refer-
may warp or degrade due to moisture
ence Fig. 4). (E) A 3 × 5-inch (7.6 ×
buildup under the plastic.
12.7-cm) galvanized mending plate
For more information on high tun-
mounted both front and back. (F) A
nels and plasticulture there are two web
0.75-inch (1.9-cm) wide, heavy-duty
sites of interest: the Penn State Center
pallet strap attached to wooden frame
for Plasticulture at <http://plasti-
with galvanized wood screws. Two
culture.cas.psu.edu> (Wodecki et al.,
screws used per side to attach the
strap to the wood. (G) Pressure-
2001) and the American Society for
treated wooden baseboard (reference
Plasticulture at <http://www.plasti-
Fig. 3). (H) Metal galvanized ground
culture.org> (American Society for Plas-
post (reference Fig. 3). (I) Finished
ticulture, 1999).
ground level. (J) Rotating wooden
stop constructed of 1 × 4 × 7-inch
(2.5 × 10.2 × 17.8-cm) finished
Literature cited
lumber. Stop attached to panel frame
American Society for Plasticulture. 1999.
with one wood screw to allow stop to
American Society for Plasticulture. 1 Mar.
rotate to upright position and allow
2002. <http://www.plasticulture.org>.
panel to swing out. (K) A 2-inch (5-
cm) overlap between edge of plywood
Lamont, W.J., M.R. McGann, M.D.
facing and end panel wooden brac-
Orzolek, E.J. Holcomb, K. Demchak, L.D.
ing.
G July–September 2002 12(3)
452

Fig. 17. Configuration of the fertilizer injector.
(A) Water inlet connection point using a quik-
connect adaptor or regular female hose connection.
(B) A 0.75-inch (1.9-cm) interior diameter (ID)
schedule-40 polyvinyl chloride (PVC) pipe, typical.
(C) Mounting bracket as provided by the manufac-
turer for the fertilizer injector. (D) Fertilizer
injector (FI). (E) Threaded pipe union located on
each side of the FI to facilitate installation and
removal of the injector. (F) A 0.75-inch ID 90º
PVC pipe elbow. (G) Straight PVC ball valve
located on each side of the FI. During normal
operations the valve position is open. (H) A 0.75-
inch ID PVC tee. (I) In-line screen filter unit with
minimum 150 mesh. (J) Pressure regulator with
adjustments from 0.5 to 5 gal/min (18.9 L·min–1)
with water pressure of 10 lb/inch2 (69 kPa). (K)
Water outlet connection point using a quik-
Fig. 16. Plastic sides are rolled up to provide ventilation of the
connect adaptor or male hose connection. (L)
high tunnel.
Vacuum feed line from fertilizer tank to FI. (M) A
0.75-inch-ID straight PVC ball valve for use in by-
passing FI. During normal operations the valve
position is closed. (N) Inlet fitting with fine screen
cover connected to feed line. (O) Liquid fertilizer
mixed in movable container. (P) Ground level or
finished grade. (Q) Pressure-treated 1 × 4-inch (2.5
× 10.2-cm) board mounted between two bows.
White, B. Dye, and E. Burkhart. 2001. The
in the Northeastern United States. Hort-
Penn State high tunnel research and educa-
Technology 3(1):92–95.
tion facility manual. Pa. State Coop. Ext.
Pub. CP02-2.
Wells, O.S. 1996. Rowcover and high tun-
nel growing systems in the United States.
Sciabarrasi, M. and O.S. Wells. 1999. Guide-
HortTechnology 6:172–176.
lines for using high tunnels for tomato
production. Univ. N.H.Coop. Ext. Fact
Wells, O.S. 2000. Season extension tech-
Sheet 2.
nology. Proc. 15th Intl. Congr. Plastics in
Agr. and the 29th Natl. Agr. Plastics Congr.
Wells, O.S. 1991. High tunnels shelter early
Appendix B, p. 1–7.
crops. Amer. Veg. Grower 39(2):44,46–
47.
Wodecki, M., W.J. Lamont, and M.D.
Orzolek. 2001. Penn State Center for Plas-
Wells, O.S. and J. B. Loy. 1993. Rowcovers
ticulture. 10 Mar. 2002. <http://
and high tunnels enhance crop production
plasticulture.c