Have you ever wished you could start growing crops earlier, but our colder Virginia winters often keep you waiting until later in the Spring? With high tunnels, you can extend the growing season, both earlier in the spring, and later into the fall!
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| Photo by NRCS |
High tunnels are unheated metal-framed structures covered with plastic that resemble greenhouses. High tunnels can protect crops from adverse weather conditions and allow for season extension earlier in the spring and later into the fall. This allows for crops to be grown outside of their normal growing seasons. This can give you a leg up at the market, providing you with earlier market-ready than your competitors, and can help you to harvest crops before their key pests come around to cause damage. The plastic covering allows light to enter, but provides a barrier to the colder temperatures. Unlike greenhouse where crops are grown in containers, crops in high tunnels are generally grown directly in the soil. High tunnels are also generally unheated, and ventilation is achieved manually or mechanically through the use of side curtains.
Location of the High
Tunnel
When planning to put up a high tunnel, it is important to orient the structure so that air will move in a perpendicular manner through the house. This will help crosswinds to cool the structure when the side curtains are lowered. Good air ventilation is key to reducing the temperature and providing a passive cooling mechanism for the structure. Avoid locating the structure near shady areas or trees that will prevent adequate light from entering. However, it is also important to note that windbreaks are important because excessive winds can damage these structures. Select an area with good soil drainage or add drainage mechanisms to help move water away from the structure.
Construction
High tunnel kits can be purchased for you to build yourself, or there are also companies that will build these structures for you. It is up to you to decide what situation would be best for you. You can find lots of information online if you choose to build your own. Even small, homemade versions will do the job and can provide the same growing conditions as larger versions.
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| Photo by NRCS |
Covering
High tunnels are covered with 6-mil greenhouse-grade polyethylene, either in one or two layers. This plastic will need to be replaced around every four to five years due to cracking and weathering. While one layer will allow for more light transmission, two-layered plastic coverings can be inflated using a blower and can help insulate and provide a buffer for wind.
Temperature
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| Photo by Chris Mullins, VSU |
Growing in protected structures requires more management than typical outdoor production. One of the biggest management concerns is controlling the temperature. When growing in a greenhouse, you can use heaters and vents. High tunnel controls are manual; therefore, they require more management. The intensity of the sun greatly determines the temperature inside the tunnel, and you are concerned with both cold and hot temperatures. Each plant has a range of optimum temperatures. Appropriate temperatures can affect plant yield, growth, nutrient/water uptake, pollination, and fruit formation. Just like cold temperatures, hot temperatures can also be detrimental to plants, so you must have a way to ventilate and allow for air movement with these structures.
End walls that open up can help with air transmission and also can provide a large enough opening for equipment to enter, such as small tractors and other implements. The most common method for controlling temps in high tunnels is through the lowering of the side curtains. Shade cloth can also be used.
An issue for high tunnel structures in the winter can be collapse from heavy snowfalls. Snow will need to be removed to prevent the heavy weight from bending the metal poles.
Irrigation
Irrigation systems are a must since the structure will be covered. Often, drip irrigation is the method used, because it is easy to install and manage. It also puts the water right at the roots. Drip systems also allow an easy way to fertilize through fertigation. Sometimes overhead irrigation may be used, depending on the crop. Rainwater catchment systems can be used as a way to collect water runoff from the roof to be used to water the crops inside.
Soil Solarization
Soil solarization is an option to help sterilize the soil and kill nematodes and soil pathogens that might be present. The soil is irrigated and polyethylene sheeting is placed over the soil. The structure is closed to allow heat in the soil to build up, ideally reaching above 110°F for two to four weeks.
Crops for High
Tunnels
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| Photo by NRCS |
Tomatoes are a very common crop grown in high tunnels. Tomatoes are fairly easy to grow, have a strong market, and perform well when grown in high tunnels. Cool season crops such as leafy greens also perform well. The use of additional row covers can help provide additional protection for these crops into the cooler winter months. Other successful crops include squash, cucumbers, cut flowers, ginger or turmeric, and berries such as raspberries and blackberries.
Pest Control
Generally, there are less pest pressures in high tunnels compared to outdoor growing. Pests that appear are typically those associated with greenhouses, such as whiteflies or aphids. Using Integrated Pest Management is important in a covered structure. Scout for insects, know their lifecycles, and determine what control methods are best suited for controlling the pest while causing the least disruptions to the environment. Biological controls such as the use of predatory insects find greater success in high tunnels, since the beneficial insects are contained.
Cost
High tunnel materials generally cost an average of $4-$6 per square foot. Construction will add an additional #2-$3 per square foot.
The NRCS (Natural Resources Conservation Service) High
Tunnel Program is a cost share option for producers to put up a high tunnel on
their farm. Some criteria for participation in the program include crop records
from previous years. The crop must be grown in the natural soil profile, and site
selection must be on sites that have adequate sunlight, a level grade or slope
not exceeding five percent. The site should be sheltered from the wind, and
avoid placing the structure in the 25-year floodplain in possible.
The high tunnel structure must be planned, designed, and constructed
from a new manufactured kit, and must be six feet in height at the peak. For
more information about cost share options, the program, and how to apply, contact
your local NRCS office.
Additional Resources:
For more information on growing under cover, visit the resources section on https://sites.google.com/vt.edu/smallscalevegprodweb/resources
References:
- Chris Mullins, Virginia State University
- https://extension.psu.edu/extending-the-garden-season-with-high-tunnels
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