Take Cover

High tunnels are quite popular with vegetable growers and can be profitable for ornamental growers, as well. These structures offer a low cost alternative or addition to heated greenhouses both in terms of the cost of the structures and inputs needed to grow a crop. The challenge appears to be managing the environment within these structures, which parallels Mother Nature much more than the controlled environment of an environmentally controlled greenhouse.

Cut flower production
It’s Friday afternoon at Dripping Springs Garden, located 50 miles east of Fayetteville, Ark., in a tiny valley along Dry Fork Creek. Mark Cain and Michael Crane are busy getting ready to bring their specialty cut flowers into the popular Fayetteville Farmers Market.

Cain took a few minutes out of his hectic summer schedule to say they’ve been using the high tunnels for about eight years on the 5-acre farm, where they grow everything organically, including cut flowers, vegetables, culinary herbs and blueberries.

Dripping Springs grows a “handful” of its 60 varieties of specialty cut flowers in the tunnels. The big advantage to the tunnels is being able to grow flowers virtually year round, even in the chilly Ozarks where it can get down in the teens and lower in the winter. In some cases, they use row covers inside the houses for extra protection on a crop such as snapdragons, which they can start as early as mid-February in the tunnels.

“It gave us an environment protected from the coldest weather,” Cain said. “We would have never tried to plant snaps in the field in mid-February. Although it can get down to 15°F inside, they can survive with a row cover.”

Dripping Springs also uses the tunnels to provide lisianthus with a longer vegetative period, to grow lilies in crates (with the aid of a shade cloth in the heat of the summer), extend the season with celosia and sunflowers, and start anemones as early as January. Cain said zinnias didn’t work so well for them due to problems with powdery mildew. Some growers are growing dahlias in the tunnels, he said.

The high tunnels are particularly useful when it comes to extending the growing season, which translates into extending the time period Dripping Springs can sell at the farmers market in Fayetteville and other local retail outlets. The tunnels also double as a growing environment for vegetables – they use them to grow peppers and eggplant in particular. Cain said the tunnels have been a good investment.

“They’re money makers,” he said.

Good for southern growers
Cut flower production in high tunnels has been practiced worldwide for several years and is increasing rapidly with growers in the United States.

Guihong Bi, Associate Research Professor at Mississippi State University, Truck Crops Branch Experiment Station, has been leading the way in research into growing cut flowers in high tunnels in the south. In trials at the 75 year-old horticultural experiment station, they have successfully grown snapdragons, dianthus, celosia and sunflowers. They also grew and carefully monitored a zinnia crop and concluded they could be grown successfully with no major disease problems. She said growing in these structures has advantages over field-grown crops in not only increasing the growing time on both ends of the season (about a month on each end), but in producing a compact crop which means higher yields; The stem length of the flowers is also longer, a quality appreciated by consumers. The high tunnels also offer protection from the wind and driving rains. And because of lower humidity in these structures, when they are properly ventilated, Bi said that diseases like powdery mildew and insect infestations are a little easier to control.

Bi said high tunnels are also a good investment for growers, with dollars spent recouped fairly quickly.

“It normally takes a year or two to recoup investment, depending on what they grow and how they market and manage the crop,” Bi said. Cain seemed to agree, saying the money spent on the smaller houses (such as a 20-foot by 40-foot house) can be recouped the first year, and the investment on a $6,500 hoop house in one or two years.

Alternative crops
For nursery owners who want to ease into bedding plant production for extra profits, high tunnels offer an opportunity without a lot of investment.

Ron Cooper, owner of Coopers Greenhouses in Kent City, Mich., uses high tunnels to finish pansies, lobelia, snapdragon and dianthus. He says the 7-foot high tunnels, which he’s had up for the past four years, work great as a natural growth regulator and even help regulate disease and insect problems.

Cooper usually places the more hardy plants in the unheated high tunnels after they’ve gotten a good start in the heated houses. He says this can help reduce disease and insect problems. He also finishes vegetable bedding stock in the high tunnels.

“Fresh air cures a lot of ails,” Cooper said.

Neil Mattson, associate professor and floriculture extension specialist, and his students at Cornell University have put the high tunnels to the test growing crops in the USDA Hardiness Zone 5 region. He said growers can gain a couple of zones with high tunnels. It’s important to make sure they’re well ventilated to avoid disease problems and overheating, he said.

“You have to be proactive,” he said.

This is particularly true in the spring when temperatures are fluctuating. He said they manually roll the sides up and down but come summer they can just leave them up.

The Cornell group has had success growing dianthus, pansies, petunias, marigolds, zinnias and other common bedding plants. He notes that the high tunnels provide a more compact plant due mostly to the cooler morning temperatures. His research has also noted a 3- to 4-degree increase in temperatures by using the row covers as needed overnight, which is achieved by trapping the heat of the soil underneath.