High tunel tomato production m00170

Contents

Authors
Lewis W. Jett, Department of Horticulture, University of Frequently asked questions about high tunnels 1
Missouri-Columbia
in collaboration with Constructing a high tunnel 4
David Coltrain
Kansas State University Producing tomatoes in a high tunnel 7
Jay Chism, James Quinn, and Andrew Read High tunnel temperature management 13
University of Missouri-Columbia
Cropping systems for tomatoes in high tunnels 15
Editorial staff
MU Extension and Agricultural Information High tunnel tomato pest management 17
Dale Langford, editor
Dennis Murphy, illustrator Marketing & economics of high tunnel tomatoes 21

On the World Wide Web Appendix: Sources of supply
Find this and other MU Extension publications on the Drip irrigation supplies 26
World Wide Web at Tomato seed 26
http://muextension.missouri.edu/explore/manuals/m00169.htm
High tunnels 27
Photographs Biological pest controls 27
Except where noted, all photographs are by Lewis W. Jett.

Acknowledgments
Research reported in this publication was funded in part
by a grant from the Initiative for Future Agriculture and
Food Systems (IFAFS), U.S. Department of Agriculture.
Thanks are due to Mr. Tim Reinbott, supervisor of the
University of Missouri Bradford Research and Extension
Center for his assistance with this research.
For further information, address questions to
Dr. Lewis W. Jett
College of
Agriculture Extension State Vegetable Crops Specialist
Food and Department of Horticulture
Natural
Resources University of Missouri
Columbia, MO 65211
Copyright 2004 by the University of Missouri
E-mail: JettL@Missouri.edu
Board of Curators

Frequently Asked Questions About High Tunnels

What is a high tunnel? ary unit, you will need to amend the soil each
A high tunnel is a solar-heated, plastic- season or year with compost or other organic
covered greenhouse with no electrical or auto- sources to maintain soil quality and fertility.
mated ventilation. It can be used to extend the
crop production season for many horticultural
When can I plant vegetables in a high
crops. Crops that are produced within high tun- tunnel?
nels are grown in the ground with drip Placing a high tunnel on your farm is
irrigation. roughly equivalent to raising the average annu-
al air temperatures in your area by 10–15
Where can I purchase a high tunnel? degrees F. Therefore, you can schedule plant-
There are several manufacturers of high ing based on field planting dates in the USDA
tunnels. See the Appendix for a list of high tun- hardiness zone directly south of your farm. See
nel manufacturers. inside back cover for zone map.

How much does a high tunnel cost? Should I grow vegetables in a
High tunnels can be built at a cost of about greenhouse or a high tunnel?
$0.75 to $1.50 per square foot. This includes Input costs for greenhouse vegetable pro-
the frame structure and the plastic cover. As a duction are significantly higher than those for
rule of thumb, you should expect to pay at least high tunnel vegetable production. Greenhouse
an additional 25 percent for end wall lumber, establishment costs approximate $6 per square
site preparation, water lines and other acces- foot, almost five times the cost of a high tunnel.
sories.
Do I need a building permit for my
What are the typical dimensions of a high tunnel?
high tunnel? Generally speaking, high tunnels are con-
Dimensions of a commercial high tunnel sidered to be nonpermanent structures.
range from 10 to 30 feet wide by 9 to 12 feet However, you may need to check with your
high by 96 to 100 feet long. local zoning regulations.
Where should I place a high tunnel on What is the optimal orientation for a
my farm? high tunnel?
A high tunnel should be placed on a level, When orienting a high tunnel, in contrast
well-drained, accessible site. High tunnels can to a greenhouse, sunlight is less important than
be moveable, but if you wish to have a station- good ventilation. A high tunnel should be ori-

College of Agriculture, Food and Natural Resources

2
High Tunnel Tomato Production Guide

ented in a direction that is perpendicular to the Other choices include peppers, summer squash,
prevailing winds on your farm. Remember, all cucumbers, melons, herbs, eggplant, and snap
ventilation is manual, so you depend on the or pole beans.
wind to ventilate your house.
Generally, for locations south of 40 degrees
What are some examples of cropping
north latitude (central Illinois, northern patterns for a high tunnel?
Missouri, southern Nebraska), high tunnels At least two crops per year can be produced
should be oriented north–south. This orienta- using a high tunnel. In central Missouri, for
tion maximizes light interception and is per- example, tomatoes can be planted as early as
pendicular to the prevailing westerly winds. March within a high tunnel, and harvest can
begin in mid-June. Depending on the variety
Should I use a single or double layer of and type of tomato chosen, harvest can con-
plastic for my high tunnel? tinue through July. At this point, the tomatoes
A double layer of plastic will almost double can be removed, the soil fertilized and tilled,
the insulation properties of the high tunnel. and a second crop of peppers, cucumbers or
However, adding another layer of plastic beans can be established for fall harvest. If you
reduces light intensity. An inflation fan will be wish to keep tomatoes in the high tunnel,
needed to blow air into the area between the spring-planted tomatoes will bear fruit through
two layers to reduce moisture buildup and October in Missouri. A cool-season vegetable
increase the insulation properties of the cover. can be planted in late November and then be
The outer layer of plastic is 6 mil and the inner either harvested or overwintered in the high
layer is typically 4 mil. tunnel.

Can a high tunnel be mobile? How are tomatoes grown within a
Yes. One of the primary objectives of a high high tunnel?
tunnel is to lengthen the harvest period. Tomatoes are grown on raised beds with
Movable high tunnels may be relocated to organic or plastic mulch. The raised bed (at
existing plots of cropland to accelerate early least 6 inches high) will facilitate drainage and
growth or extend the growing season for that keep the root system warmer. Plastic mulch
crop. However, they are less airtight than sta- (black, clear, or infrared-transmitting) will also
tionary high tunnels. Consult Eliot Coleman’s increase soil temperatures. Drip irrigation is
Winter Harvest Manual for additional informa- used to water and fertilize the tomatoes
tion on design of movable high tunnels. through the growing season. Row covers, a
lightweight fabric, must be used to provide
What type of plastic is used to cover a early frost protection. The tomatoes can be
high tunnel? either staked or caged.
Six-mil, four-year, greenhouse-grade poly-
ethylene is a suitable material for covering a
How many tomatoes can I plant in a
high tunnel. 20' x 96' high tunnel?
The optimal spacing for tomatoes in a high
How high should the sidewalls be for a tunnel is 6 square feet per plant. Therefore,
high tunnel? approximately 300 plants can be planted per
A sidewall 5 feet high is superior to a 3-foot house.
sidewall with respect to air circulation. For
tomatoes, a sidewall at least 5 feet high will per-
Is pollination of tomatoes adversely
mit air to move above the crop canopy. affected by the high tunnel?
No. Tomatoes are self-pollinated. Research
What warm-season vegetables can be at the University of Missouri has shown no pol-
produced in a high tunnel? lination problems with tomatoes in a high tun-
Warm-season vegetables are sensitive to nel. Air movement, which reduces humidity
frost. Many types of vegetables can be grown and vibrates the flower, is important for good
successfully in a high tunnel. Many growers pollination. If you have to keep the vents closed
have used high tunnels for early tomatoes. for an extended period, you may want to shake

University of Missouri Extension

3
Frequently Asked Questions

the cages or stakes to facilitate pollination. If Can I use pesticides within a high tunnel?
you are using row covers, they should be Some pesticides can be used within a high
removed when the plants are flowering and the tunnel, but growers must read the label specifi-
sidewalls are rolled up. If temperatures are pro- cally for each crop. Current regulations main-
jected to fall to 55 degrees F or less, the row tain that when high tunnel sidewall vents are
covers should remain on the plants. High side- rolled up, the high tunnel may be treated as a
walls improve cross-ventilation within the high field crop. Opening just the end walls is not suf-
tunnel. ficient for applying pesticides within a high
tunnel. When the sides are down, the high tun-
What is an average yield for high nel should be treated as a greenhouse. Keep the
tunnel tomatoes? sidewall vents open for the length of the reentry
High tunnel tomatoes average about 10–12 interval (REI).
pounds of tomatoes per plant over a four-week
harvest period (mid-June to mid-July). The
Are certain tomato cultivars best
percentage of unmarketable fruit is much lower suited for high tunnel production?
for high tunnel tomatoes than for field Any field or garden tomato will perform
tomatoes. well in a high tunnel. If the objective is to pro-
duce early tomatoes, the best choice would be a
Do I need to spray tomatoes in a high hybrid, determinate cultivar that concentrates
tunnel for disease and insect control? its fruit-set within a narrow window (4–6
High tunnels provide a protected environ- weeks). Indeterminate types will perform well
ment for crop growth. However, this does not in a high tunnel. However, these types of toma-
mean that you will not have any harmful dis- toes continue to set fruit through the summer
eases or insects. Protecting the crop from rain and fall and will not yield a large quantity of
will significantly reduce disease problems. fruit per harvest. Indeterminate tomatoes are
However, you should scout your crop for any well suited for late summer and fall tomatoes.
sign of disease. Pay close attention to the rows
nearest the baseboards or doors. Insects
Can high-bicarbonate irrigation water
encountered on tomatoes in the Universitiy of be a problem for high tunnel tomatoes?
Missouri high tunnel trials include aphids Using irrigation water that is high in calci-
(Myzus persicae), hornworms (Protoparce quin- um and magnesium can increase the pH of the
quemaculata) and fruitworms (Helicoverpa zea). soil over time and cause nutrient imbalances.
Many of these insects can be controlled by bio- Test the water for pH and bicarbonate levels.
logical methods (beneficial insects) or using Using sulfur fertilizers or injecting acids into
biological insecticides (Bt insecticides) or by irrigation water can neutralize the bicarbonates.
exclusion (closing vents at night).

For more information about high tunnels
Coleman, Eliot. 1998. The Winter Harvest Manual. (Four Season Farm, 609 Weir Cove Road,
Harborside, ME 04642)

www.hightunnels.org
Web site for the Central Great Plains High Tunnel Collaborative Project

http://plasticulture.cas.psu.edu
Pennsylvania State University Web site for high tunnel horticulture research

http://www.noble.org
Noble Foundation high tunnel research projects


4

Constructing a High Tunnel

High tunnels are solar-heated, plastic- sandy loam soil. Deep soil facilitates the forma-
covered structures that provide a protected tion of raised beds; tomatoes have a large root
environment for high-value crops. These pro- volume requiring deep, well-drained soils. Do
tective structures consist of a series of evenly not place the high tunnel in a frost pocket
spaced bows that provide structural support for where either air or water drainage is a problem.
the polyethylene covering. Most commercial Make site adjustments to allow for surface
units are available in widths ranging from 14 to water runoff. Drainage pipe can be buried
30 feet, and may vary from 48 to 96 feet long. around the perimeter of each high tunnel to
At the University of Missouri, a “Polar” high prevent water from seeping into the structure.
tunnel kit was purchased from Stuppy Select a parcel of land that is larger than what is
Greenhouse Manufacturing, Inc. (Kansas City, immediately needed to allow for expansion if
Mo.). The dimensions of this structure are 20 necessary. Additional areas may also be needed
feet wide by 12 feet high with bows spaced four to accommodate service or storage buildings.
feet apart and 5-foot high sidewalls (Figure 1). Care should be taken to avoid locations where
This structure can be up to 100 feet long. trees or buildings may cast shadows on the
solar-heated structures.
Selecting the site High tunnels should be oriented to facili-
The first step in constructing a high tunnel tate good air movement across the structure.
is site selection. The site should be relatively For maximum light interception, high tunnels
level to reduce the cost of grading. If possible, above 40 degrees north latitude (northern
select a site that has deep, well-drained loam or Missouri) should be oriented east–west. For
locations below that line, north–south is the
optimum orientation. The deciding factor
should be prevailing wind direction on your
farm. The long axis of the high tunnel should
be perpendicular to prevailing winds during
spring and summer. Cold, winter winds from
the northwest should contact the end wall.
Windbreaks on the north sides of high tunnels
may be applicable in some areas.
Access to the high tunnel is also important
when considering location. Because high tun-
nels require manual labor to vent, the structures
Figure 1. High tunnel components include sidewall, end wall, bows and purlin.
should be in a convenient location to minimize
labor cost.

Construction
Side posts Begin constructing your high tunnel by
at 4- or 6-foot spacing
positioning and squaring the four corner posts.
Guide strings after Use a hand-held level to make sure the posts
moving out half the diameter are set vertically in the ground. To check for a
of the column
square layout of the corner posts, measure each
Diagonal measure
diagonal. The lengths of the two diagonals
should be within half an inch of each other.
Use the Pythagorean theorem to set the
high tunnel square: the square of the diagonal
Batten boards
should equal to the sum of the squares of the
two sides of the high tunnel. The diagonal of a
Figure 2. Design layout for high tunnel. (Source: Nagengast, 2003).
20' x 96' high tunnel is 98.06 feet. Measuring


5
Constructing a High Tunnel

this distance for both diagonals will ensure that structure, there may be
your corner posts are set 90 degrees to each one to four purlins per
other. You may wish to cement the corner posts tunnel (Figure 4).
to add structural integrity to the high tunnel.
Set all posts to a depth of 24 inches. Metal posts Baseboard and hip
can be driven into the ground by using a metal board installation
fence post driver or by placing a trailer hitch
ball on top of the post to protect the post ends Baseboards fastened
and striking the ball with a heavy hammer. to the support posts
Run a string line from one corner post strengthen the founda- Figure 5. Baseboard and hip board attached to side
down the long axis of the tunnel to the corner tion of the high tunnel. posts.
post on the other end, drive the remaining side A 2" x 6" pressure-treat-
posts in the ground to the proper depth (Figure ed board makes a good
2). The top of each post should be the same dis- baseboard for most
tance from the string line to ensure the proper applications. Use post or
depth and to keep the bows level. conduit clamps to attach
the baseboard to the
Installing the bows side posts (Figure 5).
Most manufactured high tunnel bows are Hip boards add
delivered in two or three pieces. Stuppy’s strength to the tunnel
“Polar” unit is delivered in three sections. and serve as a top point Figure 6. Plastic attached to hip board.
Assemble a bow by joining two bow sections for rolling up the side-
with a ridge connecter to form an arch. Attach walls. Hip boards should be located 5 feet above
the complete bows to the side posts. At least two the baseboards for maximum ventilation.
people are needed to insert the bows into the Attach the hip board in the same manner as the
side posts. After the bows are in place, the cen- baseboard. Then attach a 1" x 3" board along
ter purlin can be attached to each bow with a the top of the hip board. This will serve as the
purlin bracket (Figure 3). The center purlin sits attachment point for the polyethylene cover-
on top of the bows in the Stuppy “Polar” design, ing. Pull the polyethylene over the 1" x 3"
but some manufacturers’ purlins will be board and then install another 1" x 3" board to
attached under the high tunnel bows. Additional sandwich the plastic film between the two
purlins may be added to give extra stability to boards (Figure 6).
the high tunnel. Depending on the width of the
End wall construction
End wall designs are numerous (Figure 7).
University of Missouri Research High Tunnels
are framed so that end wall panels can be
removed. Removable end walls allow larger
equipment, such as utility tractors, to be oper-
ated inside the tunnel (Figure 8). Four 8' x 8'
panels are installed on each tunnel. It is also
Figure 3. A purlin bracket (left) is used to connect the necessary to construct a storage rack near the
two bow sections. The center purlin of the Stuppy tunnel locations to allow for easy storage of the
“Polar Cub” design (right) sits on top of the bows .

Figure 4. Purlins can number from one to four on a Figure 7. Various end wall designs used on commercial high tunnels.
high tunnel.


6

panels when they are plastic to the 2" x 6" hip
removed for the sum- board with the 1" x 3"
mer months (Figure 9). boards. The cover
Attached to each panel should come over the
are two handles that top of the upper 1" x 3"
make the panels easier board and under the
to lift. Each panel is other board as previous-
held in place by four ly described. Keep the Figure 10. Wiggle (zigzag)
modified angle-iron plastic tight as you wire is used to secure the
gate latches (Figure 8). secure the covering. plastic to the frame.
The edge of the During end wall
angle iron attached to construction, attach aluminum channel lock on
the end wall framing top of the two end wall bows. This channel
was ground down to allows the plastic covering to be attached to the
make the panels easier bows by using a 13-gauge, high tensile wire
Figure 8. End wall panels are held in place by modi-
to remove. called wiggle wire, which locks the polyethyl-
fied angle-iron brackets. ene in place (Figure 10).
Covering the high Attach the sidewall plastic to a 3⁄4"-diameter
tunnel PVC pipe to allow the sidewalls to be rolled up
(Figure 11). Attach the sidewall plastic to the
Plastic films for roll-up pipe with a second PVC pipe that has
covering high tunnels been ripped in half and screwed to the roll-up
should be 6-mil green- pipe.
house-grade plastic with
UV light resistance. Handles for the roll-up sidewalls
Figure 9. End wall panels can be removed (left) and Greenhouse-grade Figure 11 shows the roll-up sidewall handle
stored (right) during the summer. polyethylene films usu- design. The PVC pipe handle is easily moved to
ally carry a manufacturer’s guaranteed life span roll the sidewalls up and down or lock the side-
of three or four years under normal conditions. walls in place. Always roll up the sidewalls in a
Covering the high tunnel should be direction that prevents water from accumulat-
attempted only when there is little or no wind. ing in the roll.
Before covering the high tunnel, rough edges
on the structure should be taped or smoothed
to prevent tearing of the plastic film. Unroll the
plastic along one side of the structure and
unfold it. For a 20-foot-wide high tunnel, you
will need a piece of plastic at least 32 feet wide.
Try not to let excessive moisture from rainfall
or morning dew settle on the film before instal-
lation. Tie a rope to one corner of the plastic
and at 20-foot intervals down the sidewall edge. Figure 11. A 3⁄4-inch PVC t-handle (left) rolls the side-
With the plastic wrapped around a tennis ball, wall vents up (open) or down (closed).
a rope can be attached to pull it slowly over the
frame. The plastic is easier to handle and pull
over the bows when it is dry. Once the film is For further information
pulled over the structure, make sure it is square Nagengast, D. 2003. Siting and building the
by checking to see that all creases run in a hoophouse. In: The Hoophouse Handbook
straight line. Attach the film to the frame in (L. Byczynski ed.) Fairplain Publications,
four or five places to secure it temporarily while Lawrence, Kan.
it is being permanently attached. Attach the


7
Producing Tomatoes in a High Tunnel


Many vegetable crops can be successfully Table 1. Plastic mulch effects on soil temperature.
grown in a high tunnel. Tomatoes are particu- Mulch type
Soil temperature increase
larly well adapted to production within a high (+) or decrease (–) (F)
tunnel because tomatoes can be trained to grow Black +5
vertically by trellising or staking. Early-season Clear +8–14
tomatoes also reward growers with premium Infrared transmitting (IRT) +5–10
prices because of the difficulty of consistently White -2
harvesting field tomatoes before July in the
Note: Soil temperature at the 2-inch depth.
central Great Plains. Source: Penn State University Center for Plasticulture
and University of Missouri.
Production inputs
A permanent high tunnel should be placed Organic mulches create a favorable environ-
on fertile, unshaded, well-drained soils with a ment for many beneficial insects while increas-
pH in the range of 6.0–7.0. Because high tun- ing organic matter. However, some organic
nels are manually vented, they should be placed mulches (straw or hay) can significantly lower
in an accessible location. The soil should be soil temperature and thus would not be effec-
tilled to a depth of 6–8 inches, and nutrients tive for warming the soil in the spring.
should be applied based on a recent soil test. Compost (being dark colored) can increase soil
Tomatoes should be established on a raised bed. temperatures, but not as effectively as black
Raised beds will significantly enhance plastic mulch. Organic mulches can be applied
tomato rooting by increasing soil warming, when soil temperatures have increased.
drainage and volume. Tomatoes are a relatively
deep-rooted vegetable. An ideal raised bed is Irrigation
Figure 12. Raised bed
about 8–10 inches high and 30–36 inches wide Because the high tunnel excludes natural with black plastic mulch
at the top. Typically, a 20' x 96' high tunnel will rainfall, irrigation must be provided. Drip irri- (1-mil, embossed). Drip
accommodate five rows of tomatoes. Raised gation for tomatoes significantly improves mar- tape is placed under the
plastic mulch.
beds can be made with power tillers or compact ketable yield and overall quality. A uniform
bed shapers attached to small tractors. After the application of water reduces fruit cracking and
raised beds are formed, fertilizer, drip tape and other physiological problems such as blossom
plastic mulch can be applied (Figure 12). end rot. The drip tape (a 3⁄4-inch small, collapsi-
ble tube) should be buried slightly below the
Mulch soil surface 2–3 inches to the side of the plant
For early tomato production, black, clear with the drippers on the top. Eight- or 10-mil
or IRT (infrared transmitting) mulch can be tape is acceptable with drippers spaced 4–12
applied to increase soil temperatures and to inches apart. A drip system operates at 8–15 psi
reduce weed emergence and soil evaporation. pressure. (See the Appendix for a list of region-
For maximum effectiveness, black plastic mulch al drip irrigation suppliers).
should be in good contact with the surface of Tomatoes use a large volume of water, espe-
the bed for effective transfer of heat. Embossed cially during fruit sizing. The fruit is about 95
plastic mulch will fit tightly over the bed. Clear percent water. From fruit set to harvest, 1.5-3
plastic will increase soil temperatures signifi- quarts of water per plant may be needed each day.
cantly more than black plastic, but weeds will Soil moisture can be monitored with a ten-
emerge under the clear film (Table 1). White siometer, a device that measures soil moisture
plastic (white on black or white) will signifi- tension in centibars (cb). The drier the soil, the
cantly lower soil temperatures and can be used higher the centibar reading from the tensiome-
for high tunnel tomato production in late sum- ter. Place the tensiometer in the center of each
mer or fall. raised bed. When 50 percent of the available
Organic mulches such as straw, hay or soil water is depleted, irrigation should occur
compost can be used for high tunnel tomatoes. (see Table 2).


8

Table 2. Using a tensiometer to monitor soil moisture and irrigate tomatoes. preplant nitrogen is necessary. However, if your
Soil texture Soil tension (cb) Soil moisture status soil organic matter is less than 3 percent, and
Sand, loamy sand 5–10 you have not been supplementing the soil with
Soil at field capacity. Irrigation is not organic residues, you should apply the equiva-
Sandy loam, loam, silt loam 8
required.
Clay loam, clay 20–40
lent of 1.4 pounds of actual nitrogen per 1,000
square feet (equivalent to 60 pounds per acre) at
Sand, loamy sand 20–40
Irrigate tomatoes (50% of soil water or before transplanting (Table 3). Additional
Sandy loam, loam, silt loam 40–60 is depleted). Provide approximately nitrogen can be applied by the drip system at a
2 quarts per plant.
Clay loam, clay 50–100 weekly rate of 8–10 pounds per acre starting
two weeks after transplanting. For example,
An additional advantage of drip irrigation assume a 20' x 96' (1,920 ft2) high tunnel has
in a high tunnel is the ability to inject water- five rows of tomatoes spaced 18" x 48". The
soluble nutrients through the drip line as the total plant population in the high tunnel is 320
plant needs them. Generally, large quantities of plants. Providing 8–10 pounds of nitrogen per
phosphorus and potassium should not be acre is equivalent to applying 19–24 ounces of
applied through the drip system. Rather, based calcium nitrate (15.5N-0-0-19Ca) per 1,000
on a recent soil test, all the needed phosphorus square feet (Table 4). A 20' x 90' high tunnel
and most of the potassium can be applied at containing 320 plants require 36–46 ounces of
planting or between cropping cycles within a calcium nitrate per week.
high tunnel. Additional potassium can be Taking tissue samples periodically through
applied during harvest. About 40–50 percent of the growing season may be useful. Randomly
the total nitrogen requirements for tomatoes select 10–12 plants per house. Break the fifth or
can be applied before planting, and the balance sixth limb from the top of the plant and place
can be applied through the drip system over the the entire limb in a brown paper bag.
course of the growing season. Nitrogen Preferably dry the sample before sending to a
requirements for tomatoes depend on the soil diagnostic lab for analysis.
quality (i.e., organic matter) and previous crop-
ping history. Generally, for each 1 percent Row covers
organic matter content of your soil, you can Row covers are an important component of
assume that there are 20 pounds of residual successful high tunnel tomato production. Row
nitrogen per acre. Therefore, if you have covers are lightweight, spun-bonded
organic matter levels greater than 3 percent, no polypropylene blankets that are supported
loosely over the crop row or canopy. In the
Table 3. Nitrogen rates for several granular commercial fertilizer analyses (pre- field, a light to medium-weight (0.5–0.9 oz/yd2)
plant). row cover will increase air temperature around
N required N per 1,000 ft2 10-10-10 13-13-13 20-20-20 the crop by 2–6 degrees F, while protecting the
(lb per acre) (oz) (oz/1,000 ft2) (oz/1,000 ft2) (oz/1,000 ft2)
crop from adverse weather and insect injury.
50 18 184 141 92
Using row covers in a high tunnel can signifi-
60 22 220 170 110 cantly increase the average daily temperature.
75 28 275 212 138 For early tomato production, row covers can be
100 37 367 283 184 two to three times more effective in a tunnel
125 46 459 353 230 than they are in the field. A medium-weight
(single or double layer) row cover should be
Table 4. Amount of several water-soluble fertilizers required to supply nitrogen
(fertigation).
placed over the plants after transplanting in
March. Do not keep row covers on the toma-
N required 15.5-0-0† 34-0-0‡ 20-20-20
(lb/acre) N/1,000 ft2 (oz) (oz/1,000 ft2) (oz/1,000 ft2) (oz/1,000 ft2) toes too long. During flowering, you will need
2 1 5 2 4 to remove the covers to ensure adequate polli-
4 1 10 4 7 nation. If temperatures become cold during
6 2 14 7 11
flowering, the row covers can be reapplied.
In contrast to field conditions, wind cur-
8 3 19 9 15
rents do not remove trapped thermal energy
10 4 24 11 19 under the row cover within a high tunnel, and
Notes: †Calcium nitrate ‡Ammonium nitrate the row cover acts as an insulating layer over


9

the plant. Another option is the use of plastic prolonged temperatures below 55 degrees or
low tunnels that act as mini-greenhouses (18- above 90 degrees, flowers can drop from the
24" high) with a single or double layer of plas- plant. High humidity (higher than 80%) can
tic (1-mil). Low tunnels can significantly also adversely affect pollination, producing cat-
increase air temperatures but must be vented to faced (misshapen) fruit. The period between
prevent excessively high temperatures. flowering and harvest is about 45 days for most
Row covers can be kept on the plants from tomato cultivars.
the time of transplanting (mid to late March) Because temperature and humidity affect
until the appearance of the first flower cluster. tomato pollination, yield and fruit quality, the
At this point, they can be removed and kept in high tunnel environment should be monitored
reserve in the event of freezing temperatures. If carefully. In early spring, the period of venting
the sidewall vents are rolled up (i.e., ambient is usually between 10 a.m. and 4 p.m. If left
temperatures are warmer than 60 degrees) the unvented, a high tunnel can reach extremely
row covers can be removed at any time. Row high temperatures (Figure 13). A 60-degree day
covers should be kept on tomato plants if the can produce 100-degree temperatures within
night temperatures fall below 50 degrees. the high tunnel. The amount of venting
required depends on prevailing winds and sun-
Tomato plant characteristics light intensity. The goal should be to keep day-
The tomato is a warm-season vegetable time temperatures between 75 and 85 degrees
crop that is sensitive to frost and will be killed and relative humidity below 80 percent. If there
by freezing temperatures. Tomato plants have is a forecast of frost, close the vents in midafter-
either a determinate or an indeterminate noon and place row covers on the plants.
growth habit. Determinate tomato vines pro-
duce side shoots that terminate in a flower clus- High tunnel tomato culture
ter, and the plant reaches a height of 3–4 feet.
Therefore, yield is concentrated over a 4- to 6- Producing transplants
week period. Indeterminate tomato plants con- In a high tunnel, tomatoes are usually estab-
tinue to produce additional vines and flower lished by transplants. The critical first step in
clusters throughout the growing season and transplant production is to purchase quality seed
may reach 5–7 feet in height. of a cultivar that possesses characteristics you
Tomato plants do not need a specific day prefer. One ounce of tomato seed contains Note:
length to flower. The flowers are self-pollinat- 6,000–12,000 seeds. (See the Appendix for a list 1 oz/gallon = 75 ppm
ed, but physical vibration of the flower by shak- of tomato seed suppliers.) The optimum germi-
ing the plant, wind movement, or insect pollination temperature for tomato seed is 75 To determine the parts
per million (ppm) of a
nation will promote pollination. The optimum degrees F, and the optimum temperature range specific fertilizer nutri-
temperatures for pollination are 68–75 degrees for growth of the transplant is 60–70 degrees. ent, multiply the per-
F at night and 60–90 degrees during the day. At Seeds should be sown in a germination flat or centage of the nutrient
50- to 72-cell tray 5-7 weeks before you antici- by 75. The product will
be ppm of the nutrient
Open
pate transplanting. Container size is important per ounce of the fertil-
Close
120 vent vent for early tomato production. Research has izer dissolved in 100
100
90
revealed that the container for a tomato seedling gallons of water.
80 should be at least 2.25 inches in diameter. For For example, if you
70 wish to prepare a 200
example, if the seed is sown in a 72-cell tray, the
Temp (ºF)

60
ppm nitrogen solution
50 seedlings can be replanted in a 606 Compack
40 of 20-20-20,
30 (2.25" x 2" cell) flat beginning at the two-true-
0.20(75) = 15. Thus,
20 leaf stage. Low light or excessive watering, in 1 ounce of 20-20-20
10
0 nitrogen or temperature will cause excessive (dissolved in 100 gal-
12 .
.

.

.
am

“leggy” growth. Transplants should be fertilized
am

.

pm

pm
.
.

.
10 .

.
.

.
am

pm

lons of water), there
am

pm
am

pm
am

pm
12

10
2

2
6

6
8

8
4

4

Time with 100–200 ppm of nitrogen per watering. are 15 ppm of nitrogen.
To make a 200 ppm
Outside High tunnel For example, approximately 1 pound of 20-20- solution, (200 ppm
20 can be dissolved in 100 gallons of water for a 15 ppm/oz) 13.3
Figure 13. Daily temperature fluctuations in an
unvented (single plastic layer) high tunnel, Columbia, fertilizer source. A good tomato transplant ounces of 20-20-20 will
Mo. (3/27/02). should be stocky. Tomato transplants can be be needed.


10

conditioned or “hardened off” before trans- First flower
planting. Hardening of tomato plants enables cluster
the plants to survive the shock of transplanting
within the high tunnel in early spring. Plants
that are not properly hardened will be slow to Leave this sucker
start growth after transplanting. Hardening of (below first flower
cluster).
tomato transplants can be accomplished by tak- Do not prune
ing plants from the greenhouse about 10 days higher on
Remove all other
the plant
before transplanting and exposing them to out- suckers below
side temperatures (no cooler than 55 degrees)
and wind for a few hours each day.

Transplanting
Tomato plants can be transplanted when
soil temperatures reach 60 degrees F at a depth
of 2 inches. A starter solution of fertilizer (e.g., Figure 16. Remove all but one sucker below the first
9-45-15) should be used to promote root devel- flower cluster to achieve balance between vine and
opment. Three pounds of the dry material is fruit growth.
mixed per 50 gallons of water and one-half pint tunnel, one of the preferred ways to train toma-
is applied to each plant. For early tomato pro- toes for early harvest is the stake-and-weave
duction, row covers, raised beds, drip irrigation system. Drive a 48–52" x 1" square wooden
and plastic mulch are essential. You may wish to stake (or metal rebar) that is driven between
invest in portable backup heaters if you feel the every other tomato plant (Figure 14). When the
risk of a freeze is great. tomato plants reach a height of 12 inches, the
A tomato plant in a high tunnel should first string can be applied. Nylon plastic twine
occupy 4–6 square feet of land. Early-yielding is the best source of string. Every 6 inches of
new growth will require a new string to provide
support for the tomato vine and fruit load.
Caging tomatoes is another option for training.
If you choose to trellis tomatoes from the roof
frame, make certain your high tunnel frame can
support the crop load. Otherwise, tensile wire
supported by metal posts can be used to trellis
the vines.
String tool Pruning, the removal of suckers or axillary
shoots that grow between the leaf and the main
stem, will accelerate early harvest and improve
disease tolerance by enhancing air circulation
around the plant (Figure 15). While pruning
may be too labor intensive for field production,
tomatoes in a high tunnel should be pruned if
Figure 14. Staking and stringing of tomato plants will improve fruit quality and the objective is early harvest. Pruning will not
early marketable yield. increase total marketable yield. The purpose of
cultivars that do not produce a large vine can be pruning is to achieve a balance between vine
spaced closer than midseason cultivars or those and fruit growth. Remove all suckers up to the
that tend to have vigorous vines. one below the first flower cluster, resulting in
two stems per plant (Figure 16). Prune when
Training and pruning the suckers are less than 4 inches long, and do
Training tomatoes within a high tunnel is not prune the plants if they are wet. After prun-
very important. When tomato are staked, light ing, you may wish to apply a labeled fungicide
Figure 15. Pruning interception and disease tolerance are improved to protect against disease outbreak.
(suckering) tomato
plants accelerates early and the plant is more likely to set early fruit, See Table 5 for a guide to troubleshooting
harvest. and disease tolerance is improved. For a high problems with tomatoes in high tunnels.


11

Table 5. Troubleshooting tomato problems in a high tunnel.

Problem Possible cause Solution

Temperatures are either too cool or too warm. Proper venting for temperature management
Flowers falling off plants
Thrips See Midwest Vegetable Production Guide for Commercial Growers
Flowers fuse together Too cool. Proper temperature management
Fruit catfaced or misshapen Pollination disorder. Humidity may be too high or temperature too low.
If the upper leaves experience cupping or
rolling, check for aphids. Aphids produce sticky Aphids can be controlled by using registered, labeled organic or
excrement that attracts flies and ants and is synthetic pesticides and releasing beneficial insects.
colonized by a dark fungus.
Cupping or rolling of leaves
Some early-season cultivars roll or cup their
Genetics
leaves when they have a heavy fruit load.
Water stress (excess or deficiency) Irrigation management
Temperatures are too high or low, or humidity Temperature management. Do not keep row covers on plants too
is excessive. long.
Poor fruit set
Flowers are not being vibrated enough for Roll up sidewalls if temperature permits. Shake tomato stakes to
pollination. promote pollen release. Use bumblebees.
Disease that is promoted by high humidity and cool, cloudy
Fruit has gray mold on the
Gray mold (Botrytis) fungus weather. Vent high tunnel properly. Use labeled fungicides, and
stem end
increase air circulation around the fruit.
Bt insecticides should be applied every 8–14 days beginning at
Border rows have fruit with
Worm feeding flowering. If worms are visible, you may wish to use another
holes. Foliage feeding.
labeled pesticide.
Stem lesions cause the
Disease Have plants diagnosed by your local extension specialist.
plant to wilt.
If picking during hot weather, use a shade cloth. Late fall tomatoes
Fruit fails to ripen Temperature
may not ripen because of low light and temperatures.
Blossom end rot is caused by a localized deficiency of calcium to
the developing fruit. Make sure your soil has medium to high
Black spots on bottom of calcium levels; water uniformly; do not overapply NH4 fertilizers or
Blossom end rot
fruit
overprune. Calcium can be applied through the drip system. Do
not apply foliar calcium.
Fruit cracking Irregular watering Mulch and water uniformly.

Table 6. Some tomato varieties for high tunnel production.
Days to Disease
Variety Comments
harvest resistance
Determinate
BHN 543 72 F12 V1 Midseason early; Excellent size, shape and quality.
Carolina Gold 75 F12 V1 GW Yellow (tangerine) colored fruit; Vigorous vine. Excellent quality.
Florida 47 75 F12 V1 Large, smooth, crack-resistant fruit; Good quality; Vine slightly less vigorous than Fl 91.
Florida 91 72 F12 V1 Large, smooth, crack-resistant fruit. Heat-set variety with good disease tolerance.
Floralina 72 F123 V1 Large, smooth, crack-resistant fruit. Very good taste.
Merced 69 F12 V1 Early; Good quality. Has a tendency to crack in the field but not the high tunnel.
Mountain Fresh 78 F12 V1 Excellent midseason variety; Very good quality. Vigorous vine. Good disease tolerance.
Mountain Spring 70 F12 V1 Early; Excellent fruit size.
Sunleaper 70 F12 V1 Heat-set variety good for summer and fall production.
Indeterminate
Trust F12 V1 Excellent quality and yield
Big Beef 73 F12 V1 Excellent yield
1Thislist is not intended to include every variety that may perform well in a high tunnel.
F = Fusarium wilt race 1, 2, 3 V = Verticillium wilt GW = Gray wall


12

Figure 17. Tomatoes can be packed in single- (15 lb) or multiple-layer (20–25 lb) boxes for market.

Variety selection or shipping containers for tomatoes vary.
Typically tomatoes are packed in 20- to 25-
The essential first step in successful high- pound boxes or single layer, 15-pound boxes
tunnel tomato production is selection of a suit- (Figure 17).
able variety. Table 6 lists several varieties that Do not refrigerate vine-ripe tomatoes or
have performed well in high tunnel trials at the allow the fruit to be exposed to temperatures
University of Missouri. higher than 85 degrees. If tomatoes are held in
storage, the temperatukre should be 50–75
Harvest and postharvest handling degrees F with 85–90 percent relative humidi-
Tomatoes can be harvested for vine-ripe ty. On hot days, pulp temperature of tomatoes
fruit about 45 days after flowering. However, can be 20 degrees warmer than air tempera-
tomatoes continue to ripen when picked at any tures. Picking fruit early in the morning or in
stage from mature green onward. If high tunnel the evening reduces field heat. Shade cloth can
tomato production is extended into late fall, significantly lower temperatures in the high
mature green fruit can be harvested before a tunnel during harvest in late June and July.
hard freeze and allowed to ripen at room tem- Tomatoes can be packed immediately after har-
perature. Mature green fruit can also be harvest without washing, or growers can clean the
vested and allowed to ripen at room tempera- fruit with chlorinated water. If the fruit is
ture. Mature green fruit exhibits a color break washed, do not use ice or cold water, and the
in the shape of a star at the blossom end. water should be properly chlorinated for sani-
Another way to gauge maturity is to cut the tation (125 ppm). The pH of the wash water
fruit, and if the seeds are cut, the tomato is not should be 6.5–7.0. A washing and sizing unit
ready to harvest. can be used to clean and size harvested fruit.
Tomatoes are graded as USDA No. 1, No. Avoid storing vine-ripe tomatoes with fruits
2, and No. 3. Within each grade class, tomatoes such as apples or cantaloupes. These fruits
can be sized as jumbo (more than 3.5" diame- emit ethylene, a gas hormone that accelerates
ter); extra large (2.75" to 3.5"); large (2.5" to ripening of tomatoes and can reduce their shelf
2.75") and medium/small (less than 2.5"). Boxes life.

Also from Extension Publications 1-800-292-0969
MU publication MX 384, Midwest Vegetable
Production Guide for Commercial Growers, 177 pp.
This comprehensive guide, revised annually, gives a wealth
of information on how to protect your vegetable crops from
insect and disease pests. It contains reference sections for
planting, spraying, cultivating, harvesting and storing more
than 30 vegetables common to the Midwest.
In addition, dozens of tables give information on varieties,
maturity dates, handling and storage life, estimated yields
per acre and more for each vegetable.


13
High Tunnel Temperature Management

High Tunnel Temperature Management

Temperature management is one of the Extremely high temperatures (above 90
most critical components of successful high degrees) can cause tomato flowers of some cul-
tunnel tomato production. Early-season toma- tivars to abscise and will prevent the tomato
toes can be successfully grown in the central from developing a uniform red color. High
Midwest without supplemental heat. Using temperatures cause the tomato leaves to turn
raised beds, plastic mulch and row covers in the brown at the margins; the plant looks almost as
high tunnel will significantly increase average if it has been in a furnace. Using shade fabric
daily temperatures. Adding a second layer of (30–50%) from late June through July harvest
polyethylene covering will reduce heat loss and will significantly lower
the formation of condensate on the inside sur- temperatures within the
face of the cover. Growers who wish to use high tunnel.
heaters may find them useful in protecting the Shade cloth can be
crop during a hard freeze and in accelerating applied externally over
growth of the tomatoes. the high tunnel in June
The optimum temperature for growth of and removed in early fall
the tomato plant is 70–75 degrees F. Average (Figure 18). The shade
daily temperatures should not be lower than 65 cloth should not cover
degrees. Temperatures below 55 degrees dur- the sidewall vents. To
ing flowering can reduce fruit set and produce calculate the width of
misshapen fruit. Growers must monitor tem- shade cloth needed, use Figure 18. Shade cloth applied over the high tunnel
moderates midsummer temperatures.
peratures carefully by placing a minimum/max- the following formula
imum thermometer in the center of each high for a semicircular (arched) structure:
tunnel at the height of the tomato canopy. ((W/2) x 3.14) – (Hsw x 2),
Shade the thermometer to avoid false high
readings due to direct exposure to sunlight. where W = width of the high tunnel and Hsw =
For early-tomato production, April is the height of the sidewalls.
most variable month for temperature within the Figures 19–25 show daily temperature
high tunnel. Often, the vents are adjusted three cycles throughout the 2003 growing season as
or more times per day to maintain an optimum recorded in the University of Missouri high
temperature. Roof vents or vents at the top of tunnel trials.
the end walls may be useful in preventing exces-
sive heat and humidity buildup within the high 100
90
tunnel.
80
70
120 60
50
Temp (ºF)

100
40
80 30
Temp (ºF)

20
60
10
40 0
1 5 9 13 17 21
20 Time (hours)

0 Outside High tunnel
1
6
11
16
21
26
31
36
41
46
51
56
61
66
71
76
81
86
91
96

Time (hours) Figure 20. March 15, 2003. Tomatoes were trans-
Outside Inside Inside
planted. Ambient conditions were sunny and warm.
(no rowcover) (rowcover) All vents were closed. The average 24-hour tempera-
ture in the high tunnel was 56 degrees F relative to
Figure 19. January 16-20, 2003. Row covers (double 51 degrees F ambient temperature. The growing
layer; lightweight) were used to overwinter lettuce degree day (gdd) base temperature for tomatoes
with excellent results. below which growth is negligible is 51 degrees F.


14

80 90
70 80 Vents
closed
60 70
60
50
50
40
Temp (ºF)

Temp (ºF)
40
30
30
20 20
10 10
0 0
1 5 9 13 17 21 1 5 9 13 17 21
Time (hours) Time (hours)
Outside High tunnel Outside High tunnel

Figure 21. March 30, 2003. Ambient conditions: Cool, Figure 22. April 4, 2003. Warm morning, then turning
sunny with vents closed. Twenty-four hour tempera- colder through the day. Winds WNW; vents opened
ture average within the high tunnel was 48 degrees F on east side and closed at 3 p.m.
compared with 36 degrees F ambient conditions.

120 90
80
100
70
80 60
50
60
Temp (ºF)

Temp (ºF) 40
40 30
20
20
10
0 0
1 5 9 13 17 21 1 5 9 13 17 21
Time (hours) Time (hours)
Outside High tunnel High tunnel Outside High tunnel
& row cover
Figure 23. April 21, 2003. Flowering of tomatoes Figure 24. May 31, 2003. Ambient conditions: Cloudy,
observed. Ambient conditions: Cloudy, cool morning; cool. Vents open until 6 p.m.
Sunny afternoon. Vents closed. Single layer of light-
weight row cover used.

100
90
80
70
60
50
Temp (ºF)

40
30
20
10
0
1 5 9 13 17 21
Time (hours)

Outside High tunnel High tunnel/
shade cloth
Figure 25. July 4, 2003. Tomato harvest. Shade cloth
(47% black) significantly lowered temperatures and
improved ripening of high tunnel tomatoes.


15
Cropping Systems for Tomatoes in High Tunnels

Cropping Systems for Tomatoes in High Tunnels
Seed tomatoes

Seed lettuce
Relay tomatoes Transplant for transplants
Seed carrots
Seed lettuce

into lettuce and basil
Relay lettuce Seed beets,
for transplant

into tomatoes carrots, spinach,
transplants brocoli, kale &
Relay 2nd tomato into tomatoes
crop (grape) lettuce
carrots

under row covers
into basil

Jan. Feb. March April May June July Aug. Sept. Oct. Nov. Dec.
Harvest Harvest Harvest basil Harvest Harvest
lettuce Harvest lettuce grape lettuce
& carrots tomatoes
tomatoes

Remove basil
Intercropping system plants

Figure 26. A hypothetical intercropping system for tomatoes in a high tunnel in central Missouri.

Intercropping is the growing of two or be relay planted into the existing lettuce bed
more crops within the same production area (Figure 28). Because the root systems of lettuce
during part of the life cycle of each crop. and tomatoes do not compete, fertilization prac-
Intercropping in a high tunnel allows growers tices for the tomato can be used for both crops
to produce many vegetables within a limited without diminishing the yield of either. Lettuce
space and thus improve the output of the high harvest begins in April and extends through
tunnel. Interplanting one vegetable with anoth- mid-June. Peak yields of lettuce occur before
er after the first vegetable has become estab- tomatoes set fruit. Tomato harvest begins in
lished is called relay intercropping (Figure 26). mid-June and extends through July. The lettuce
does not accumulate nitrates. Both crops are
Cropping system I able to maximize yields without competing with
Tomatoes interplanted with lettuce each other.
Starting in January, leaf lettuce can be direct
seeded onto preformed raised beds within the
high tunnel (Figure 27). Each raised bed is
24–30 inches wide by 6–10 inches high. The let-
tuce is direct seeded as two or three rows per
bed, 6–8 inches apart. In March, tomatoes can
Figure 28. Lettuce, carrots and basil are among the crops that can be intercropped
Tomato successfully with tomatoes in a high tunnel.
plants
Cropping system II
Tomatoes interplanted with carrots
Carrot &
lettuce Carrots can be seeded as soon as soil tem-
understory peratures reach 45 degrees F. For example, car-
rots can be seeded from February through early
April in a high tunnel. Tomatoes can be relay
6-8 in.
6-8 in.
interplanted into the carrot bed with no loss in
6-10 in.

yield of either crop. The carrots can be harvest-
ed one month to one week before harvest of the
24-30 inch width tomatoes begins.
Figure 27. Cool-season crops can be interplanted with
tomatoes in preformed raised beds.


16

Cropping system III 90
Tomatoes interplanted with basil 80

Percent emergence
70
Basil is often listed as a companion plant
60
that repels tomato hornworm. It can be relay
50
planted (from transplants) into existing tomato
40
beds in early July after the carrot or lettuce har-
30
vest has concluded. Basil is a warm-season herb
20
that grows well in hot weather. Harvest of basil 10
will typically run from early August through 0
October. The tomatoes can be left in place or

Sp oc
Be
Le

Sp

Br

Ka
Ta

br li
ec co
o
t

e

i

t

le
tu

na

so

cc
removed after peak harvest in late July. Grape

ts

ia li
ce

ch

i

o

lty
or cherry tomatoes can be planted into the
existing beds with basil. Row covers No row covers

Figure 29. Row covers for winter crops significantly
Cropping system IV improve germination.
Overwintering cool-season vegetables Source: Data from University of Missouri Research
High Tunnels, 2003.
After final harvest of tomatoes in mid to
late November, a 100-day cool-season produc- nel (Figure 29). The lettuce, spinach, miscella-
tion window opens in the high tunnel. Hardy neous salad greens and kale can be harvested
vegetables such as broccoli (specialty and head- before mid-March in central Missouri. Other
ing), kale, spinach, tatsoi, carrots, beets and let- cool-season vegetables may require a longer
tuce can be direct seeded, germinated and over- season.
wintered under row covers within the high tun-


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