High tunnel facilities — less complex, less expensive versions of a greenhouse — can offer Mid-South growers a way to extend the growing season for production of high value locally-grown fruits, vegetables, and cut flowers.
Made of ribs of plastic or metal pipe covered with a layer of plastic sheeting, high tunnels are easy to build, maintain and move, according to the USDA, which has launched a three-year program to verify the effectiveness of the facilities.
All Mid-South states have signed up to participate in the program, which offers cost-sharing through the Natural Resources Conservation Service.
“There is great potential for high tunnels to expand the availability of healthy, locally-grown crops,” said Kathleen Merrigan, deputy secretary of agriculture, in announcing the program.
“This program will give us real-world information that farmers all over the country can use to decide if they want to add these facilities to their operations. We know that these facilities can help producers extend their growing season and, hopefully, add to their bottom line.
The study will verify if high tunnels, also known as hoop houses, are effective in reducing pesticide use, keeping vital nutrients in the soil, extending the growing season, increasing yields, and providing other benefits to growers.
A recent high tunnel field day at the Mississippi State University Truck Crops Experiment Station at Crystal Springs drew more than 300 persons from the Mid-South area, says Mengmeng Gu, MSU assistant Extension professor of plant and soil sciences.
She discussed the production system with Mississippi Women in Agriculture at their annual conference at the Mississippi State and gave a tour of research facilities on the university’s south farm.
While at first glance it may be difficult to tell the difference between a high tunnel and a conventional greenhouse, she notes that high tunnel facilities are usually freestanding or gutter-connected structures that have no heating equipment or electrical power.
“They use passive ventilation for air exchange and cooling and an irrigation system to facilitate crop production,” Gu says. “A high tunnel can be a simple as pipes or other framework covered by a single layer of greenhouse grade 4- to 6-mil plastic, or it can be as complicated as many greenhouses.”
There are many forms of high tunnels, she notes. The simplest is a single (one-bay) freestanding ground-to-ground Quonset-shaped structure. Multi-bay high tunnels with two or more bays have each bay sharing the side wall with the next bay. High tunnels can also be lean-tos against walls or can be built into hillsides.
The simple frame structures she is using for her project are 30 feet x 96 feet, covered with a sheet of solid plastic, and cost about $6,900 each, she says. They are tied down with mobile home anchors.
“High tunnels provide protection for crops, compared to open field production. They are used mainly to increase temperature in early spring, fall, and sometimes winter, or to moderate the fluctuation of temperatures for crop production.”
Because there is no electricity, there are no automated cooling or heating systems. Cooling is through roll-up sides and large open doors at each end. With walls and doors closed, heating is by naturally trapping solar heat during the day and keeping it in through the night. In the event of extreme low temperatures, portable heaters or other methods may sometimes be used to protect crops.
“High tunnel production doesn’t require as much capital investment as greenhouse production,” Gu notes, but provides a greater level of environmental protection than field production.
“With high tunnels, growers can start planting earlier in the spring and thus have an early harvest, allowing them to obtain premium prices for off-season produce. Crops can also keep producing when the temperature is too cold for field production in the fall.”
The facilities also offer better quality and improved yield, she says, which can add to profit potential. “A high tunnel also keeps out rain, which means less moisture on foliage and less chance for disease.” They also offer protection from wind and storms.
Weed problems can also be better controlled, since most high tunnel crops are grown with plastic mulch and drip irrigation. “Weed seed germination is reduced tremendously,” Gu says, “because there is no natural rainwater in the tunnels, which greatly limits soil moisture where no crop is grown.”
When the tunnel is closed, crops are protected from bird and deer damage, and screens can be installed to keep out insects when the tunnel is open.
Mississippi and the central Gulf Coast states have low annual temperatures in the teens and single digits in most years, she notes. “In winter, average daily high temperatures range from the upper 40s in the northern part of the state to the upper 50s in the southern areas. But they can vary widely, with highs in the 60s and low 70s on many days.
“Combined with monthly rainfall of 3.5 inches to more than 5 inches in most places December-February, the outdoor environment doesn’t encourage most winter vegetable crops.”
High tunnels, Gu says, may allow production of lettuce, herbs, and many other crops that are impossible to grow outdoors in Mississippi winters.
“Unlike northern states, where prolonged periods of cold temperatures limit growing crops in the winter, the average maximum and minimum daily temperatures in the Mid-South are suitable for growing many crops in the winter. Farmers here face the obstacle of a limited growing season often only because short spells of sub-freezing temperatures during the winter and early spring put crops in danger.”
High tunnels are “a low cost technology to temper the environment and reduce the environmental and economic risks of year-round production,” she says.
Gu cautions, however, “This is not a lazy man’s project. It takes more work and attention than for field grown crops. The better your management, the more you can get out of it.”
(To sign up or learn more about EQIP assistance for high tunnel projects, contact your local NRCS office.)