TUNNEL VISION

February 20, 2011 at 12:00a.m.

Unheated ‘hoop houses’ stretch growing season

Akron Beacon Journal

AKRON

Imagine eating just-picked lettuce or a freshly dug carrot from your garden — in February.

High tunnels make that possible.

High tunnels, or hoop houses, are simple structures that cover either an in-ground garden or a collection of raised beds. They allow a grower to increase yield and extend the season, in some cases right through winter.

They’re sort of like greenhouses, except they’re unheated and much cheaper to build.

The tunnels are getting a lot of attention lately among farmers, thanks in large part to the U.S. Agriculture Department’s funding of 2,422 high tunnels in a pilot project to test their effectiveness. But high tunnels have applications for backyard gardeners, too — at least the ones who are passionate about growing food and ambitious enough to commit to the extra attention the tunnels require.

A high tunnel is simply a frame, usually made of metal, that’s covered by plastic sheeting. It’s called “high” because it’s tall enough to walk or perhaps even drive inside, as opposed to a low tunnel — a similar hooped structure that covers just a single row or a raised bed and stands only a few feet tall at most. The high tunnel’s height allows it to accommodate plants at their full height, so it can cover a crop from beginning to end if the grower wants it to.

Growers often use high tunnels to start plants earlier in spring and keep them producing later into fall. Some also use them in winter for cold-hardy crops such as spinach, chard and lettuce, said Matt Kleinhenz, a horticulturist at the Ohio Agricultural Research and Development Center in Wooster Township and a vegetable specialist for the Ohio State University Extension.

The plastic on a high tunnel changes the ecosystem inside in a number of ways, most notably by warming the air and soil. On a recent sunny day when the outside temperature was 25 degrees, it was 70 inside one high tunnel Kleinhenz uses for research at the agricultural research center.

But the benefits go beyond warmth, said Kleinhenz and Joe Kovach, an entomologist at the center. High tunnels protect plants against wind, blowing particles and extreme temperature fluctuations. They confuse some insect pests, which perceive the space as a black hole and don’t venture inside.

“Plus, it doesn’t rain in there,” Kovach noted. That means plants are less susceptible to various types of rot, and gardeners can work no matter what the conditions outside.

By controlling the environment and extending the season, high tunnels produce higher yields than unprotected gardens, Kleinhenz said.

But there are drawbacks, he and Kovach noted. High tunnels require extra attentiveness — particularly in spring and fall, when a sunny day can quickly heat a tunnel that’s been closed to protect against the normally cooler weather. The tunnel needs to be vented promptly, or the plants inside could die.

High tunnels are also vulnerable to windstorms, and their maintenance can be labor-intensive. Kovach jokes that the two worst days of his year are the day he puts the plastic coverings on his three-season tunnels and the day he takes them off.

There’s an expense involved, too. Kleinhenz said most commercial high tunnels cost $2 to $9 a square foot, depending on the features.

A do-it-yourselfer could make a simple tunnel for less, using metal pipe and special plastic sheeting with a UV inhibitor that keeps it from breaking down as quickly as unprotected plastic. The special plastic should last about three to five years, Kleinhenz said.

Mail-order retailer Johnny’s Selected Seeds even sells a tool designed for bending hoops for high tunnels out of the top rails normally used for chain-link fences.

Eliot Coleman has been experimenting with growing plants under cover since the late 1970s and now has eight high tunnels at his Four Season Farm on the coast of Maine. He uses them to grow tomatoes, eggplants, cucumbers and peppers during Maine’s cool summers, and spinach, Asian greens, carrots and scallions in winter.

Originally, he used cold frames to extend his growing season, he said. But after he had to dig to find them following one particularly bad snowstorm, he decided he needed something that put a roof over both him and his crops.

He’s since written books about high-tunnel gardening, including one aimed at backyard gardeners titled “Four-Season Harvest.”

High-tunnel gardeners “just need to think of August and September as the second spring,” a time for planting a second crop that will be harvested in winter, he said. As long as those plants are well-established when winter arrives, harvesting can continue, even though the plants won’t grow much when the days are short.

Coleman’s high tunnels have two layers of plastic, which produce growing conditions more similar to Georgia’s than New England’s.

Kovach said each layer of plastic has the effect of moving one hardiness zone south.

Plants grown in a single-layer high tunnel in Northeast Ohio would experience a growing season similar to Kentucky’s, he said. Add a second layer of plastic or put low tunnels over the growing beds inside the structure, and the season is more like southern Tennessee’s.

The tunnels require effort, but to Coleman, they’re worth it.

“It’s just the delight of having freshly harvested crops in winter,” he said.