High Tunnel Production
High tunnels resemble greenhouses, but they vary widely in the level of environmental controls. Some high tunnels rely heavily on passive rather than active ventilation (such as fans) for temperature and humidity control. Other high tunnels use computers to control roll-up sides, gable fans, and heaters. High tunnels are generally covered with a single layer of greenhouse-grade polyethylene film (six mil) instead of the air-inflated double polyethylene layer found in greenhouses. High tunnels usually have removable ends that are not found in standard double polyethylene greenhouses to allow access for soil and planting bed preparation equipment.
Marketing
Well-managed high-tunnel operations can have substantial marketing and cash flow advantages. By increasing the production season by as much as eight weeks prior to field production season, growers can gain a “first to the market” advantage. By reducing the time lag between the last crop from the previous season and the first crop of the current season, customers are much less likely to seek alternativesuppliers. This reduced time lag not only comes from an earlier season, but also by extending the season for up tosix weeks after the first outdoor frost event. Reducing farm downtime improves a farm’s bottom line by maintaining cash flow well beyond that found on farms that produce only outdoors.
Early- and late-season produce often command higher prices. High-tunnel-grown tomatoes often sell for two to four times the price of field-grown simply due to the limited availability of locally grown tomatoes until field season begins in earnest. Other crops, such as bell peppers, can experience high losses in the field when allowed to fully ripen to red, yellow, or orange. Research at Penn State has demonstrated that growing bell peppers in high tunnels dramatically increases pack-out percentage. More recent research has found similar advantages when growing cucumbers in high tunnels. Higher prices and greater pack-out are necessary to offset the increased costs of production using high tunnels.
Types of Structures
In recent years, the number of high-tunnel manufacturers has increased dramatically, providing growers with a wide array of design and equipment options. Stand-alone structures are either Quonset (semi-circle shape) or Gothic-style (A-frame and similar roof lines) types. Both high-tunnel shapes are commonly used throughout the U.S. The disadvantage of the Quonset-type high tunnel is its potential to collapse under heavy, wet snowfall. Gothic-style or peaked high tunnels have had no problems under the same snowfall events since the A-frame roof allows snow to fall off the roof and not accumulate over time. A concern for all high-tunnel structures is high wind (exceeding 60 mph). Whether the high-tunnel structure is constructed parallel to or perpendicular to the prevailing wind direction may not be as critical as the width of the structure and number of purlins added to reinforce the high tunnel. Follow manufacturer's recommendations on constructing the tunnel for the optimum wind defense and how the sides should be set based on predicted winds. Some designs recommend that in high winds, both sides of the high tunnels be rolled down to enhance air flow over the tunnel and minimize damage, while others require their sidewalls to be fully open.
There are also multiple-bay high-tunnel structures available. Due to the larger area covered, this type of structure has the potential to be used for the production of small fruit or tree fruit crops (such as sweet cherries, grapes, raspberries, blueberries, strawberries, peaches, and apricots) as well as more typical crops such as tomatoes, peppers, cucumbers, cut flowers, and greens. These large multi-bay units come in sizes ranging from 0.5 to 10 acres. Although there is somewhat greater potential for wind damage in this type of structure, wind damageto multi-bay tunnels can be reduced by venting thepoly,which allows the air pressure inside and outside the tunnel to equalize.During high temperatures, when multi-bays are already vented to reduce heat and humidity,they routinely withstand 70 mphthunderstorm gusts. When the temperature is low(April and May), multi-bay tunnels can be completely closed during the more typical high winds of 30 to 40 mph that occur.
Production Practices
The keys to successful horticultural crop production in high tunnels are crop scheduling and ventilation. When planting vegetable crops in the spring in high tunnels, it is generally recommended that you transplant the crop about four to six weeks earlier compared to your earliest planting date in the field on bare ground. If you push this date earlier, the need for supplemental heat increases. Floating row covers can also be used inside the tunnel to protect crops. If unusually cold night temperatures occur several days to weeks after planting the vegetable crop in the high tunnel, a portable, clean-burning heater can be placed in the high tunnel until more seasonal temperatures return to the location. Many growers choose to permanently install greenhouse-type heaters that are controlled by thermostats to ensure an early, damage-free crop. Sunlight is the limiting factor to how early a crop can be started. Until about the middle of February or beginning of March, there is insufficient sunlight for crop growth regardless of how warm it is in a protected structure. Because high tunnels are usually placed in the field perpendicular to prevailing wind direction, the most critical component of the system is ventilation. Maintaining optimum growing conditions inside the high tunnel without having extreme temperature fluctuations is critical to produce early high-yielding and high-quality horticultural crops. Internal temperatures should be checked several times a day and the roll-up sides adjusted accordingly to protect the crop. Many growers have modified their tunnels with computer and thermostatically controlled automated vents, fans, heaters, and roll-up sides to eliminate the need to regularly monitor the internal temperature and make manual adjustments to ventilate the structure.
There are many variations in growing methods depending on the crop, time of planting, and available labor. High-tunnel growers often use a tunnel-within-a-tunnel method to get plants off to a fast start or to maintain production of cold-weather crops such as spinach and greens throughout the winter. The use of floating row covers or low tunnels can greatly improve cool-season crop production by trapping heat directly in the crop canopy versus having the heat escape into the full tunnel.
Crop Selection
Crop selection is of paramount importance to operating a high tunnel profitably. Although almost any horticultural crop can be grown in a tunnel, some crops have substantially greater potential for making a difference in your farm’s bottom line. Typical high-tunnel crops include tomatoes, peppers, cucumbers, strawberries, greens, herbs, and cut flowers. Your specific crop selection should be based on local market potential and the projected dollar return per unit of production area. When possible, select cultivars that have a determinate or compact growth habit. This will make management tasks such as pest control and harvesting easier as the plants mature in a crowded tunnel environment.
The primary high-tunnel disease challenges, powdery mildew (on many crops), and leaf mold (on tomatoes), are much more readily managed when vegetation is managed to provide for greater air movement. This removes both heat and moisture, thus lowering the relative humidity within the tunnel. Spider mites, aphids, and thrips are the primary arthropod and insect pests found commonly in tunnel production. In-row and between-row spacings must be managed to allow room to apply treatments, whether traditional pesticides or biological controls. Horticultural crops are produced more efficiently on raised beds with plastic mulch and drip irrigation.
Because of the width and height of high tunnels, a smaller, modified plastic mulch layer is available for use in high tunnels. These mulch layers will make a three- to four-inch-high bed, eighteen inches wide, using thirty-six-inch-wide plastic mulch. The beds are spaced on forty-four-inch centers; thus, a seventeen-foot-wide high tunnel can accommodate four beds, while a twenty-one-foot-wide high tunnel can accommodate five beds. The drip tape is generally placed two inches deep and can be set either in the center or just off center, depending on the crop. For tomatoes, the tape is placed on one side of the bed and a single row of tomato plants is planted down the middle of the bed. For peppers, the tape is placed in the middle of the bed and two rows of plants are set diagonally on either side of the drip irrigation tape, eighteen feet apart in the row. Other crops such as greens and cut flowers may require a second line of drip tape due to higher planting densities.
Fertilization
Fertilizing tunnel crops is no different than for those grown in the field. All of the same materials can be used in the tunnel environment including dry and liquid fertilizers, composts, and animal manures. Apply 40 to 60 percent of yourcrop’s projected requirements prior to tilling the soil and forming the raised beds. This should be based on soil testing and knowledge of your crop’s nutrient requirements. Among the many sources of nutritional information, one good source of information for nearly every horticultural crop is Knotts’ Handbook for Vegetable Growers. Before making the raised beds, broadcast any preplant nutrient material and incorporate into the top six to eight inches of the soil. Compost and manures should be applied in small amounts (about one inch in depth) to the soil surface prior to incorporation. Any additional nutrients can be injected through the drip irrigation tape during the growing season, based on crop need as determined by tissue sampling at two-week intervals. Organic growers will need to apply 70 to 80 percent of a crop’s projected nutritional requirements prior to planting because organically approved fertilizers that are compatible with drip injection systems are substantially less concentrated than those available to conventional growers.
Pest Management
Pest management in a high tunnel is different from growing the same crop in the open field. The complex of pests differs because of the controlled environment. The exclusion of rain and the use of drip irrigation and mulches greatly reduces weeds and diseases. Because of the need to ventilate a high tunnel, many of the same insect pests are present, but often pests more commonly encountered in greenhouses are also present. To obtain long-term control of pests that is effective and economical in this complex environment, high-tunnel growers need to use an integrated pest management (IPM) approach.
IPM employs a combination of methods to help manage pest problems. These methods include biological control, cultural controls, mechanical and physical controls, and selective use of pesticides. IPM focuses on ecosystem strategies that provide long-term pest prevention. Biological controls use natural enemies, including predators, parasites, pathogens, and competitors, to control pest populations. Cultural controls include use of resistant varieties, tillage, and sanitation to help manage pests. Mechanical and physical controls include such items as traps, mulches, and barriers that either kill the pest directly or block access to the crop. Pesticides should be used only when monitoring indicates they are absolutely needed.
Monitoring to identify which insects, weeds, or diseases are present is the key to effective use of IPM practices and ultimately the profitability of your high-tunnel enterprise. Daily scouting of plants and insect traps will provide you with the data you need to decide which IPM methods you need to employ.
Tips for Successful Vegetable Production with High Tunnels
- Use raised beds (three to four inches high) when laying plastic mulch to ensure better water and nutrient management in the high tunnel.
- When laying plastic mulch in the high tunnel, make sure the soil has sufficient moisture to form a good, raised bed. Transplant into soil that is moist enough to sustain your new plants.
- Wait at least two to three days after laying plastic mulch in the high tunnel before transplanting vegetable transplants through the plastic mulch to allow for the plastic mulch to increase soil temperatures.
- Monitor the weather carefully and be ready to provide supplemental heat if necessary to keep plants growing actively from the time they are planted. Most crops in high tunnels can be damaged if air temperatures drop below 45°F.
- Use actively growing, insect- and disease-free vegetable transplants that are the optimum age for the specific vegetable being transplanted in the high tunnel. Also, inspect all transplants prior to planting into the high tunnel and remove all transplants that have aphids, whiteflies, thrips, or any other insect on them; plants that have any lesions or spots on either leaves or stem; and any weeds that are growing in the transplant trays.
- After transplanting vegetables through the plastic mulch, monitor soil moisture levels underneath the plastic mulch with a tensiometer or irrometer, and maintain soil moisture levels by using drip irrigation.
- Scout vegetable plants regularly for aphid, thrips, spider mites, and whitefly populations and other pests. Pest populations can rapidly increase under tunnel conditions and do substantial damage to young transplants and reduce your total marketable fruit yield. Blue and yellow sticky cards placed in the plant canopy are commonly used to monitor insect populations and should be checked daily and replaced weekly.
- For crops that are planted very early, be ready to remove row covers, thermal blankets, or low tunnels to facilitate pollination. Most growers using high tunnels find that purchased colonies of bumblebees increase both the quality and quantity of fruit. These should be ordered several weeks in advance of required delivery time.
- Fertigate as necessary based on tissue testing throughout the growing season.
Following these tips will help ensure that your high-tunnel investment is profitable. High tunnels require more management than producing the same crop in the field. Additional pest scouting and monitoring are required because of the confined space and increased plant densities. However, producing crops when others are not can command higher prices and an increase in profitability.
Environmental Impacts
In the normal course of operations, farmers handle pesticides and other chemicals, may have manure to collect and spread, and use equipment to prepare fields and harvest crops. Any of these routine on-farm activities can be a potential source of surface or groundwater pollution. Because of this possibility, you must understand the regulations to follow concerning the proper handling and application of chemicals and the disposal and transport of waste. Depending on the watershed where your farm is located, there may be additional environmental regulations regarding erosion control, pesticide leaching, and nutrient runoff. Contact your soil and water conservation district, extension office, zoning board, state departments of agriculture and environmental protection, and your local governing authorities to determine what regulations may pertain to your operation.
Risk Management
You should carefully consider how to manage risk on your farm. First, you should insure your facilities and equipment by consulting your insurance agent or broker. It is especially important to have adequate levels of property, vehicle, and liability insurance. You will also need workers’ compensation insurance if you have employees. You may also want to consider your needs for life and health insurance and if you need coverage for business interruption or employee dishonesty. For more on agricultural business insurance, see Agricultural Alternatives: Agricultural Business Insurance.
Second, check to see if there are multi-peril crop insurance programs available for your crop or livestock enterprises. There are crop insurance programs designed to help farmers manage both yield risk and revenue shortfalls. However, individual crop insurance coverage is not available for all crops. If individual coverage is not available for what you grow, you may be able to use the Whole Farm Revenue Protection (WFRP) program to insure the revenue of your entire farm operation. Information from your Schedule F tax records (or a “Substitute Schedule F for WFRP Purposes” if you do not file a Schedule F) from the past five consecutive years is used to calculate the WFRP policy’s approved revenue guarantee. Operations that have expanded over time may be allowed toincrease the approved revenue amount based on an indexing procedure. Depending on the number of commodities grown, you have the choice of coverage of 50 to 85 percent of your approved revenue. Coverage and premium costs depend on the level of diversification in your operation; the maximum level of insured revenue is $8.5 million (based on maximum adjusted gross revenues of $17 million and the 50 percent coverage level). WFRP also provides replant coverage if itis not already covered under an underlying individual crop policy. More information on WFRP can be found at.Whole-Farm Revenue Protection (WFRP) at the USDA Risk Management Agency website. Finally, the USDA Farm Service Agency has a program called the Non-Insured Assistance Program (NAP) that is designed to provide a minimal level of yield risk protection for producers of commercial agricultural products that don’t have multi-peril crop insurance coverage. NAP is designed to reduce financial losses when natural disasters cause catastrophic reduction in production. A basic level of coverage(50 percent of expected production at 55 percent of the average market price) is available for a fee of $325 per crop per county (fees are capped at $825 per producer per county, but not to exceed a total of $1,950 for producers growing crops in multiple counties). Higher levels of protection at the 50-, 55-, 60-, and 65-percent levels at 100 percent of the average market price are available for an additional premium. NAP coverage is available through your local USDA Farm Service Agency office. This program may be used for producers with less than an acre of production for many crops. The application fee for this program may be waived for eligible limited-resource farmers.
Sample Budgets
Included in this publication are two cost-of-production budgets for tomatoes grown in the high tunnel. The first is for an early-spring-planted crop of tomatoes, and the second is for two crops produced within a year. The first crop is an early-spring-planted crop followed by a late-summer-planted crop scheduled to mature after field-grown tomatoes are no longer available. A summer crop of microgreens could be produced between the two crops if you desire. The budgets assume the production in a 25-foot by 128-foot-high tunnel without heaters.
These sample budgets should help ensure that all costs and receipts are included in your calculations. Costs and returns are often difficult to estimate in budget preparation because they are numerous and variable. Therefore, you should think of these budgets as an approximation and make appropriate adjustments using the “your estimate” column to reflect your specific production situation. More information on the use of crop budgets can be found in Agricultural Alternatives: Budgeting for Agricultural Decision Making.
Sample Budget Worksheets
For More Information
Dawling, P. The Year-Round Hoophouse: Polytunnels for All Seasons and Climates. Gabriola Island, BC, Canada: New Society Publishers. 2018.
Harper, J.K., S. Cornelisse, L.F. Kime, and J. Hyde. “Budgeting for Agricultural Decision Making.” Agricultural Alternatives series. Penn State Cooperative Extension, March 2019.
Maynard, D. N.. Knott’s Handbook for Vegetable Growers, 5th Edition. Hoboken, NJ: Wiley Publishing. 2006.
Mefferd, A. The Greenhouse and Hoophouse Grower’s Handbook: Organic Vegetable Production Using Protected Culture. White River, VT: Chelsea Green Publishing. 2017
Online Resources
United States Department of Agriculture (USDA) Planting in a High Tunnel
United States Department of Agriculture (USDA) – Natural Resources Conservation Service (NRCS) "Growing All Seasons: High Tunnels"
“High Tunnel Crop Production Tips” by Lewis W. Jett. Sustainable Farming on the Urban Fringe, New Jersey Agricultural Experiment Station, Rutgers Cooperative Extension
University of Kentucky High Tunnel Production Resources
Iowa State University High Tunnel Crop Production
Initial Resources
Initial Resources Spring Crop
- Land 1 acre
- Labor 120 -150 hours
- Capital $20,000 - $30,000
Initial Resources Double Crop
- Land 1 acre
- Labor 250 - 275 hours
- Capital $20,000 - $30,000
Note: This publication is intended to provide only general information about legal issues and should not be construed as providing legal advice. It should not be cited or relied upon as legal authority. State and federal laws vary by situation, and no attempt is made to discuss laws of states other than Pennsylvania. For advice about how these issues might apply to your individual situation, consult an attorney.
This publication was developed by the Small-scale and Part-time Farming Project at Penn State with support from the U.S. Department of Agriculture Extension Service.
