What It Is
Hoophouses are what they sound like—miniature, unheated greenhouses, constructed from a series of metal hoops covered with plastic, set over a patch of soil or a raised bed to trap heat. "It's a fairly low-tech thing to build," says Roger Doiron, founder of Kitchen Gardeners International, a nonprofit dedicated to promoting the use of backyard gardens as a means for creating a more sustainable food system. "Essentially, what you need is a support structure," he says, which can be PVC tubing or standard metal pipes. "Cut that to the size you need, and poke both ends into the ground in an arc." Once you have a row of hoops that's as long or short as you need, cover them with plastic, and you're finished. (Doiron recommends downloading hoophouse plans from a local extension service for a more detailed how-to.)
One advantage to hoophouses, Doiron notes, is that they're easily modifiable. You can construct a small hoophouse to cover a single row," he notes, or build one large enough for you to walk into. The simplest hoophouses can cost as little as $50 for materials. A caution, though: Because these structures are so lightweight, Doiron advises that you make sure your hoophouse is well secured, so it doesn't blow away in a stiff wind. Install the posts deep in the ground, and be certain that the plastic cover is well secured with staples or tacks.
You've built your house, now read on for what to plant inside it.
What to Plant
Most people assume that growing seasons are defined by temperature, but it's the amount of daylight that really allows crops to thrive. And by February 15th, most regions of the country will have 10 or more hours of daylight, which is the minimum amount plants need. The plastic traps in heat and allows you to plant crops much sooner than you could without the added protection. "When we had our hoophouse, I felt like I was about two months ahead of the game," says Doiron. It also lengthens your growing season, he adds, by trapping heat and warming the soil, which allows you to keep tomatoes growing a few weeks into fall. "In cool northern climates, you can start with the crops you'd be planting a couple months later in the spring, things that can germinate in cool soil," he says, such as radishes, salad greens and other hardy Asian greens, beets, carrots, turnips, green onions, and cilantro.
As temperatures warm up, you can keep using your hoophouse for summer tomatoes, melons, and peppers, he adds. That's provided you keep it ventilated; it's usually enough to make sure one end of your hoophouse has a flap that you can open to let heat escape, Doiron says. "They really do capture a lot of heat, too much to be used [year-round] in southern areas," he says, "but with proper ventilation in northern climates can use them throughout the year."
If you're interested in installing a hoophouse in your backyard, but you're intimidated by the DIY construction, you can order kits online from Hoophouse.com and other garden suppliers.