K-State Research and Extension News
July 31, 2009
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Plastic, Unheated Greenhouses Changing U.S. Market Garden Output

OLATHE, Kan. – Hoop houses (also called high tunnels) can seem as revolutionary as throwing a big tarp over some hay bales and calling it a barn.

Yet, hoop houses are now giving an edge to an expanding group of U.S. farmers who grow vegetables, fruits or cut flowers where cold weather is no stranger. These farmers can market fresh-picked strawberries months before and months after their area’s traditional growers have anything to sell.

“High tunnels aren’t what you’d call high tech. The typical one is simply a PVC- or metal-structured polyethylene Quonset hut. It’s no more than a unheated, plastic greenhouse that you can ventilate by hand. Even so, it protects plants from the weather – sort of like a big cold frame would,” said Ted Carey, horticulturist with Kansas State University Research and Extension.

Their simple nature gives hoop houses lower construction and operating costs, compared to those for a nursery-grade greenhouse. Farmers commonly recover their investment within a year or two, Carey said.

“For me, the only strange thing about them is how long and how far the United States lagged behind other countries in adopting high-tunnel horticulture,” he said. “An American named E.M. Emmert invented the structure, calling it a field greenhouse. He came up with the idea at the University of Kentucky right after World War II.”

Carey has just completed his own research to assess how the U.S. situation is finally changing. He found adoption rates differ from area to area. Hoop house size can vary just as widely. Overall, however, U.S. high tunnel use has been increasing rapidly for more than a decade. Land-grant university research and Extension programs are supporting the rise, as are innovations that growers themselves develop.

“The protection that the tunnels provide is doing more now than just allowing market farmers to schedule production through an extended growing season,” he said. “It’s expanding the kinds of plants farmers can grow, taking some production into the arena of specialty crops. It’s also reducing or eliminating some of the impacts of damaging sunlight, wind and hail. It’s increasing both yields and crop quality.”

Hoop house adoption is actually improving farmers’ disease and pest management, too, according to the land-grant university horticulturists whom Carey surveyed. And, the higher quality crops are beginning to  capture premium prices.

The survey found the U.S. Northeast is leading in terms of individual hoop house numbers, although parts of the Midwest are gaining ground quickly. By far, tomatoes and salad ingredients are the top crops.

Apparently, however, the states with the most acreage under high tunnels are in zones where cold weather isn’t a big crop risk -- California, Arizona, Hawaii, Oregon and Florida. The two largest-acreage states are using most of their high tunnels to raise raspberries or landscape plants. Hawaii has 50 percent of its hoop house acres in flowers. Oregon is specializing in blackberries and blueberries.

“The situation is getting pretty interesting,” Carey said.

In contrast, before 1990 the great majority of U.S. adopters were in the nursery industry, he said. Because high tunnels can be semi-permanent, temporary or moveable, many nurseries used them to overwinter container plants that didn’t sell during the previous growing season.

“Adding to their cost savings, nurseries could truthfully say the structures are temporary – even if their own high tunnels never moved. That made a difference in their property tax assessments,” Carey said.

By the early 1990s, hoop houses had become the No. 1 structure in a $4 billion a year U.S. greenhouse industry, but they accounted for less than 2 percent of the world’s total. Research released in 1993 indicated hoop houses were covering more than 482,000 acres of land (21 billion-plus square feet) around the world. China, Japan and Korea accounted for 50 percent of that area.

“In other words, the structures already are helping to produce enormous amounts of food in many parts of the world,” Carey said. “In the United States, they are a nursery industry staple, and they’re finding a place from small-scale market gardens to our larger scale produce farms. In fact, they’re helping today’s farmers respond to the rising demand for fresh, locally grown produce.

“Even so, I suspect we Americans are just beginning to see the possibilities.”

Since 2003, K-State has hosted a High Tunnel Web site (http://www.hightunnels.org/) with original material geared for educators, as well as growers. It provides useful links and the signup for an e-mail listserv widely used by growers, researchers and allied industry personnel to ask questions and exchange information about high tunnel use.

The Extension horticulturists at the universities of Missouri and Nebraska help maintain the Web site, which was established as part of a U.S. Department of Agriculture-sponsored project to test and promote high tunnel systems in the central Great Plains.

For the audio slide story on this subject, go to: http://www.oznet.ksu.edu/news/slides/Project_plants/index.html.


K-State Research and Extension is a short name for the Kansas State University Agricultural Experiment Station and Cooperative Extension Service, a program designed to generate and distribute useful knowledge for the well-being of Kansans. Supported by county, state, federal and private funds, the program has county Extension offices, experiment fields, area Extension offices and regional research centers statewide. Its headquarters is on the K-State campus, Manhattan.

Story by: Kathleen Ward
K-State Research & Extension News

Ted Carey is at 913-856-2335 or tcarey@ksu.edu.