Leopold Center for Sustainable Agriculture

Producers extend crop seasons using high tunnel production

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By LAURA MILLER, Newsletter editor

Even after a chilly, wet spring, Sean Skeehan and Jill Beebout were able to sell their signature tapestry salad mix on opening day at the Des Moines Farmers Market in early May.

Skeehan and Beebout operate Blue Gate Farm near Chariton where they grow vegetables on about 1.5 acres. Although most of their crops are grown outdoors, they also have selected varieties ripening inside two high tunnels.

A high tunnel is constructed of bent metal pipe attached to metal posts and covered with a layer of polyethylene. Technically not greenhouses because they have no heat or forced ventilation, high tunnels help Iowa producers extend the growing season both in spring and fall. In mid-summer, Skeehan and Beebout will have ripe tomatoes about a month earlier than other growers.

That’s the competitive advantage that Linda Naeve and Ray Hansen were looking for when they conducted a two-year research project for the Leopold Center’s Marketing and Food Systems Initiative. Naeve and Hansen, who work with Iowa State University Extension’s Value Added Agriculture program, studied yield potential, profitability and market distribution options in high tunnel systems.

Over the past two seasons, horticulture researchers Hank Tabor and Paul Domoto grew multiple varieties of several high-value crops in high tunnels and outdoors at two locations: in central Iowa at the ISU Horticulture Research Farm north of Ames and in southwest Iowa at the ISU Armstrong Research Demonstration Farm in Cass County. The crops included tomatoes, bell peppers (green and colored), raspberries and blackberries, pole beans and Greek oregano.

“The high tunnel project clearly identified that there is potential profitability but it comes with a whole new set of management issues,” Naeve said. “The success of a high tunnel enterprise requires careful planning and a clear business strategy for success.”

They found that crop diseases were reduced, but insect pest management needs increased with high tunnel production. Not all crops were profitable, and the best combination is a plan that includes multiple crops per year. Tender varieties of raspberries and blackberries that produce larger fruit than the hardy outdoor varieties grown in Iowa fared well inside the tunnel, but the plants needed careful management.

Many environmental factors can be controlled inside the high tunnel. Plants are watered via drip irrigation. Temperature can be changed by raising or lowering the plastic sides of the tunnel. Row covers can provide some protection during cold weather, enabling some crops to be grown until late October in Iowa. Many diseases that might cause problems in crops grown outdoors create fewer problems inside the tunnels.

However, a high tunnel system has little defense against elements of Iowa’s volatile weather such as high winds and hail. A 70 mph wind gust knocked down the tunnel at the Armstrong farm in May 2008, and again in July. A tornado destroyed the Blue Gate Tunnel on May 30, 2008; they restored the structure in August and added a second tunnel this past March.

“That’s a real testimony, that Blue Gate found it profitable to replace the high tunnel and add another one,” Naeve said. “There’s a great future in this growing system because young growers and existing farmers can diversify their production but you need to know how to manage them.”

Naeve and Hansen are working on a second phase of their “Tunnels to Tables” project. They are producing a workbook and seven-hour training module. “Our intent is to share what we’ve learned through research at ISU and what other growers have experienced by trial-and-error so new growers won’t have to learn from their mistakes,” Naeve said.

Back to Leopold Letter Summer 2009