High Tunnels in New Jersey

High Tunnel Construction

High tunnels are a simple, relatively inexpensive, and effective way of protecting high-value crops from the effects of marginal low temperatures, wind, rain, some insect and foliar disease pests, as well as wildlife damage. Although use of high tunnels have been increasing in Northeastern states, here in New Jersey they remain underutilized. There is ample opportunity for expanding high tunnel production, without saturating NJ markets.

High tunnel growing offers season extension, yield and quality improvements, reduction in fertilizer leaching, reduction in costly pesticide and fungicide inputs, and quick payback on capital investment. They are an answer to many farmers’ problems, if you are willing to manage the technology. Daily raising and lowering of the plastic sides each morning and evening (sometimes more often) is required to control temperature and humidity.

Earlier production means capturing your customers earlier in the season, keeping them season long with companion field production, and long into the fall. This equals higher sales, at reliably higher prices, from higher marketable yields per unit area. Providing earlier, consistently available, quality crops enables you to compete in upscale markets. What’s not to like?!

High tunnel costs and management are “scalable.” Meaning they offer equal “farm size neutral” benefits to smaller as well as larger farms, rather than requiring a large farm economy of scale, to realize their benefits. As a New Jersey farmer, whether large or small, long established or just starting out, ask yourself, “Are high tunnels a way to improve my farm’s bottom line? Can they work for me, in my situation?”

High Tunnel Design

High Tunnels are impermanent structures designed for ease of construction and mobility. The ideal design for New Jersey farms is metal pipe framing with a gothic or angled bow configuration that can withstand snow load and wind. The top bows are attached to metal posts that have been driven into the ground. Plastic covering is typically 6-8 mil polyethylene with UV inhibitors to extend life. Build a tunnel to suit your needs; think about the width and height required to work inside the tunnel with farm machinery for soil tillage and crop management. Also, remember tunnel length impacts worker productivity.

High Tunnel Site Selection and Construction

High Tunnel benefits are most pronounced when sited correctly, taking into consideration: good sunlight, away from shadows cast by trees or buildings; well-drained soil; airflow; and water access.

It is important to ensure adequate pervious surface around the base of the structure to make sure no water flows or seeps into the high tunnel or results in runoff. Avoid clearing the area around the tunnel and/or compacting the soil, but instead allow vegetation (non-crop, non-weed) to grow in the area so that rainwater is absorbed.

Orientation is critical to ensure movement of prevailing winds through the tunnel sides.

Components of a High Tunnel

Components of a High Tunnel A. Rib, Hoop, Arch, Bow
B. Purlin, Ridgepole
C. End Wall
D. Hip Board
E. Side Wall
F. Baseboard

Component Costs for Manual Roll-Up and Motorized Roll-Up High Tunnel


Managing Conditions Inside the High Tunnel

When to Plant: Seedlings can be transplanted into high tunnels 4-5 weeks earlier in the season than they could be transplanted into fields.

Single vs. double layer poly cover: In general a high tunnel will provide about 7 – 10 °F increase in average daily temperature. Adding a second layer of plastic will increase the temperature approximately 10°F while reducing light intensity by approximately 7%.

Using Raised Beds & Mulches: As in field production, raised beds enhance soil warming and drainage. Raised beds should be 6-10” high and 24-30” wide. Four foot spacing between raised beds allows five in a 20’ wide high tunnel. Beds can be formed with compact bed shapers or power tillers. After the beds are formed, fertilizer, drip tape, and mulch can be applied.

hightractorCrop Rotation: As in the field, high tunnels culture utilizes crop rotation as a method of keeping soil borne pathogens in check and managing nutrients for a sound soil health program. Maintaining High Tunnel Rotations discusses this in more detail.

Bag culture: This is a way to have more precise control of crop growth and to better manage diseases. Instead of growing plants in soil under the high tunnel, bags are filled with a commercial or grower-prepared peat lite formula. The plants receive water and fertilization through an automatic drip irrigation system.

Plant Spacing: Spacing crops in high tunnels is similar to spacing the intensive field cultivation. Consult local commercial production guides. Typical spacing for tomatoes in a high tunnel is 18-24” within rows and 4’ between rows. In a 20’ x 96’ high tunnel, this accommodates approximately 300 plants.

Row Covers: Row covers – permeable to light, water, and air – can be an important component of production resulting in an additional 2-8 degrees of warmth.

Crop Support: Cultural practices for trellised crops in field production are similarly recommended in high tunnels. The trellis may be wires or strings from the structure instead of poles in the soil, depending on need.

croprotationWatering: Drip tape is the preferred irrigation method to supply uniform application of water and fertigation in high tunnels.

Fertilization: Soil testing is recommended. High tunnels may require less total fertilizer application than field conditions.

Ventilation: High tunnels are passively vented structures, generally with manually operated side vents. In most regions they should be oriented perpendicular (at right angles) to the prevailing winds on your farm. Good cross ventilation will remove humid air and moderate air temperatures during the day. Keeping humidity in the high tunnel from reaching a high level (>85%) is crucial for preventing many diseases.
Excessive high temperatures: Shade cloth and roof vents are effective ways to moderate temperatures, where this is a problem.

Rescue Heating: While high tunnels typically do not have a heating source, portable heaters may be used in an attempt to save the crop from damaging temperature drops. Thermal blankets, row covers, and water bags can also be utilized for back up frost protection.

Diseases & Pests: Growing plants in high tunnels often decreases the need for pesticide and fungicide applications. Select varieties that are disease resistant, especially in high tunnel culture. Start with disease-free seed or transplants. This may require hot water treatment by you, the grower, before seeding. Grafting, in some crops, is another method to combat plant diseases. Avoid intermixing of vegetables and potted ornamentals in the same tunnel.

Sanitation in and around the tunnel: Remove and destroy any diseased plant parts as soon as they are found. Encourage workers to perform daily tasks in tunnels prior to fieldwork, so clothes, footwear, tools, and implements like tillers, tractors, or carts are used in the tunnel before fieldwork, and cleaned off appropriately before returning to tunnels.

When crops are finished, deeply incorporate, remove, destroy or compost at a distance, as appropriate, plant materials, including crop roots. Do not permit escape volunteer plants to become established in the structures at any time. Volunteer escapes and weeds can be a source of insects like aphids or thrips, and can also serve as vectors of virus diseases.

Pollination: Crops which need pollination in order to set fruit include melons, some cucumbers, squash and berries. If the native population of bees is not low, bees may enter the high tunnel naturally. However, many growers either hand-pollinate or purchase bees for pollination.

Harvesting: Most crops are harvested at least a month earlier than field grown crops. Harvesting into the fall can be prolonged at least a month later by this method. Three cropping cycles are realistic for high tunnels (2 warm season, one cool season).

Economics & Marketing

The economic benefits from high tunnels have been well documented. Their use is a sustainable practice. High tunnels allow for season extension, which translates directly into increased profitability. Often early and late season produce command premium prices. By excluding rain, plants grown under this system have reduced weather defects and disease pressure. Plants are protected from wind and wildlife damage. Weed seed germination is reduced tremendously due to less soil moisture where crops are not grown.

Funding Availability

The USDA, NRCS, and SARE have initiatives encouraging the use of high tunnels. Visit their websites for more information.
USDA/NRCS http://www.nrcs.usda.gov/wps/portal/nrcs/main/nj/programs/
NE SARE http://www.nesare.org

Sources & Resources

General Information About High Tunnels

High Tunnel Construction


High Tunnel Economics

Journal Articles

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