High tunnel structures offer a new tool for farmers
PETERSBURG, Va., Aug. 16, 2007 – As farmers know, the growing season is limited by freezing weather in early spring and late fall. However, they do have a tool for extending the season and increasing output: high tunnel structures.
These structures, which Chris Mullins, research specialist for Virginia Cooperative Extension at Virginia State University, has been studying, are akin to low-tech greenhouses. They provide a simple means for protecting crops from freezing weather at the ends of the season. By harvesting crops during non-peak times, farmers will have an advantage over the competition by providing something that is not widely available.
High tunnel structures work, said Mullins, because they shelter crops from cold weather. Like a greenhouse, they consist of an arched metal framework extended over a rectangular plot, usually 21 feet by 48 feet. This provides about 1,000 square feet of growing space. This framework is covered with plastic sheeting, and its walls are framed with wood.
High tunnel structures do not rely on heaters or fans, so there is little maintenance involved. Instead, the high tunnel structure will retain solar heat during the day, which can keep the air inside above freezing even when the outside temperature drops to 24 degrees.
On both sides of the structure, the plastic rolls up, creating a 5 foot to 6 foot opening, which can be opened and closed as necessary. The sides are usually opened during the day to prevent overheating (even during colder months it can reach up to 70 degrees), and closed in the afternoon to insulate the vegetables for the cold night ahead. The end walls can also be removed to allow a tractor or other implement to be used inside the structure.
Not only do high tunnel structures allow farmers to extend their growing season, but they also provide additional benefits. The structures protect crops from the rain, so fungus and disease become less of an issue. The optimized conditions also allow for a slightly increased yield per square foot, Mullins said, because the absence of rain allows plants to be grown closer together.
The barrier from the outside also lowers insect pressure, and allows farmers to use biological pest control – beneficial insects which are applied to eliminate specific pests. Because insects are less of a problem, pesticides need not be applied as heavily, and farmers may be able to use a natural, biological spray instead.
Many consumers who have eaten high tunnel structure grown crops have noted better taste in these foods. This may be due to the lowered amount of chemicals used in production, Mullins said.
There is little operating cost involved with owning a high tunnel structure. While they cost about $2 to $2.50 a square foot, they can pay for themselves in as soon as a year. Mullins said two crops could be grown during the year, one in March through July, the other July until fall. The income from these two crops will easily pay for the structure.
Though temporary, high tunnel structures will last up to 10 years, although the plastic covering may only last three to four years. Mullins said that these structures are not intended to replace traditional techniques. Rather, they must be integrated into the whole farming process, used just like another tool or piece of equipment.
Although high tunnel structures are cost effective, they are labor intensive. A farmer must check on a structure daily, making sure to regulate temperature appropriately by raising or lowering the roll-up side. Furthermore, the shelter the structure provides from the rain also means that the crops inside must be irrigated on a regular basis. Mullins said that drip irrigation is primarily used, which is augmented with fertilizer injectors.
High tunnel structures are most appropriate for producers with fewer acres who sell their products directly at market. Though the structure's cost effectiveness largely depends on what type of produce is grown within its walls, Mullins said that tomatoes, broccoli, Brussels sprouts, strawberries, greens, herbs, cherry trees, and brambles have all been successfully produced in high tunnel structures.
Contact: Chris Mullins
Research Specialist
Virginia Cooperative Extension
Virginia State University
(804) 524-5834
cmullins@vsu.edu
Contact: Michael Sutphin
Writer
Communications and Marketing
College of Agriculture and Life Sciences
Virginia Tech
(540) 231-6975
msutphin@vt.edu
Writer: John Rougeux
Student Intern
Agriculture and Extension Communications
Virginia Tech