Column: Seeds & Stems

Tomm Becker hasn’t been afraid of a spring frost killing the lettuce, tomatoes, cilantro, kale and chard he’s growing at Sunseed Farm.

That’s because he’s growing them under the plastic cover of a 30-by-96-foot hoop house, which since last fall has been a source of vegetables through most of the winter.

Hoop houses let the sun in, and the solar-powered heat warms up the soil and keeps tender plants from freezing in early and late frosts. When a strong wind flapped the hoop house cover at Sunseed Farm last week, it blew through the openings where the plastic had been hoisted to provide ventilation. The day before had brought cold temperatures and heavy rains that flooded the nearby rye field, so the side flaps had been down to keep the heat in.

“The great thing (about hoop houses) is you can control everything,” Becker says.

Hoop houses aren’t just for farms – a backyard hoop house can give anyone a head start on the season. Then even into the winter, you can grow some cold weather crops – like lettuce – or store root crops, like carrots.

But like anything else in your garden – ponds, chickens, a compost pile – a hoop house is a project that never stops.

Small Farms, Year-Round Local Produce

The Sunseed Farm hoop house is working so well for Tomm and Trilby Becker that they’ll be getting another one in about a week at their farm off Joy Road, just northwest of Ann Arbor. In time, they want to have about five hoop houses to grow a variety of vegetables throughout most of the year for members of their CSA (community-supported agriculture) program.

The Beckers’ hoop house, along with several others in the area, were built with microloans from Repasts, Present and Future, an organization run by Lisa Gottlieb and Jeff McCabe to support local farmers. [Much of their funding comes from donations raised during their weekly breakfast salon – Friday Mornings @ SELMA – held at their home on Ann Arbor's west side and featuring local chefs and locally produced food.]

With hoop houses, says Gottlieb, a local farm can produce food for most of the year. “For our climate, hoop houses are really something terrific,” she says.

Hoop houses allow you to control, to some degree, the microclimate within the structure. When the sun is shining and the temperature is going up, you can open the vents to cool down the heat that can easily climb to more than 100 degrees, even in the winter. And when the heat increases, the humidity also builds up. After a while, the plants just can’t breathe, Tomm Becker says.

Of course, there are things that are beyond anyone’s control. During the winter, clouds and cold – along with the shorter daylight hours – will keep pretty much anything from growing. “In late December and January,” says Becker, “everything is pretty much in stasis.”

The trick is to plan ahead, planting crops late in the past season that can be picked in the dead of winter, he says.

It’s also tough to control what gets into that hoop house, which can be a warm and comfortable place for greens-eating critters – like mice and voles – during the winter. And some insects, like aphids, will find a warm, moist hoop house their idea of heaven. Moisture also is a wonderful medium for growing fungi, which is not good unless you’re raising mushrooms.

Backyard Hoop Houses

If you’re interested in simply feeding yourself and your family, you might be able to get by with a 1,500-square-foot hoop house, says John Hochstetler, who has four hoop houses that provide about 6,000 square feet of space for growing vegetables and flowers for the market. It can even be pretty cheap, he says, if you save your own seeds.

The first thing to do is figure out what you want in a hoop house. “If you don’t know what you’re doing,” says Hochstetler, “it’s going to be a big mess.”

Get some good materials, including heavy duty plastic and a framework that will stand up. Hochstetler’s first hoop house was built with plans he found online, and PVC piping from a big box store. The first heavy snowfall smashed his work flatter than a bug. Lesson learned, Hochstetler now builds his hoop houses with steel frames.

If you’d like to start with something a little smaller, Ann Arbor architect Dave Sebolt has designed a hoop house measuring roughly 12-by-12 feet that costs about $200 to build. And it’s got a shape that will keep the snow load from building up.

“The one I put together has a little roundedness on the top,” Sebolt says. “It gets into a 40-degree slope, more a parabolic arch. If the angle is 45 degrees or steeper, the snow will slide off.” (Click here to download a copy of his plans.)

He also found that snow piled around the base of the structure might cause the ribs to collapse at the ground level. His solution is to simply clear that snow away. It might also help to mulch along the base or use foam to keep out the critters.

Sebolt also suggests that hoop house builders stretch the side plastic down into the ground, to better anchor the structure against any winds that might tip it over or fly it off to Oz.

There are advantages to larger hoop houses. Smaller structures can overheat quickly. Larger ones also can overheat, but it will take longer. By the same token, larger structures will take longer to cool, which keeps frost off from the plants more effectively.

No matter what the size or the season, you’ll have to keep an eye on the temperature. Sebolt recommends using heat pistons that expand with the heat to open ventilation windows and contract when the temperature cools, so that the windows close.

The heat/cold, moisture and sun principles are the same whether you’ve got a commercial-size hoop house, a portable cold frame that fits over a single bed or something as simple as a glass bell jar or the bottom of a plastic milk carton.

I don’t have anything like a hoop house in my yard, because the space is just too small. But I might be able to use something like a cold frame, which is just a wooden box with a cover that lets in light and keeps frost away from transplants.

They can be small, portable and much cheaper than a full-fledged hoop house. You could put a 5-by-10-foot cold frame together for as little as $25 if you use recycled materials – using an old shower door for the top of the cold frame, for example. Ann Arbor’s ReUse Center or Habitat for Humanity’s ReStore are great places to look for what you need.

About the writer: Marianne Rzepka, former reporter for the Ann Arbor News and Detroit Free Press, is a Master Gardener who lives in Ann Arbor and thinks it’s fun to turn the compost pile.