Roots and Shoots: Extend the Growing Season

Make use of cold frames and hoop beds

By Pamela Doan

Impatient for the homegrown flavor of vegetables? I am. This winter seems to be lasting forever. Summer’s harvest can’t come soon enough. I’ve been looking into projects to extend the growing season. I’ve found creative approaches to reusing materials that are mostly laying around the garage that don’t require a carpenter’s skill level or special tools to assemble and can get fresh veggies onto the table sooner this spring with a little luck.

A tiny shoot coming up under the snow. Get a jump on spring with a cold frame or hoop bed. Photo by P. Doan
A tiny shoot coming up under the snow. Get a jump on spring with a cold frame or hoop bed. Photo by P. Doan

Years ago before she went to prison, I watched an episode of Martha Stewart Living where Martha built a cold frame. Since it’s Martha Stewart, of course she claimed it was easy, but I was put off by the labor involved. Her method had some poor guy digging a double-coffin size hole several feet deep in the ground to serve as the frame.

Cold frames can actually be any size and can sit on top of the ground; they don’t have to be set in. The main characteristics are that it has four sides and a transparent cover or lid that latches. The rest is up to the builder or designer. Angled sides make it easier to lift. Use wood that is untreated as treated wood may leach chemicals into the soil.

The cold frame can be set into the ground enough that it’s securely in place. If it’s going to be filled with organic matter to plant in, make sure it’s deep enough to hold the soil and give sufficient space for the tallest plants to reach their full height. If you’re fortunate enough to have good soil, then plant directly in the ground. The cover and protection of the box will keep the plants toasty through winter.

I read about a few tricks to trap solar heat on Mother Earth News that I’ll share here. Make a solar heater by filling containers that are painted black with water. Plastic water jugs, freezer bags, or just about any decent size vessel that will hold water will do as long as it is painted black. It will retain and project heat. Fresh manure placed in a hole in the dirt will give off heat as it decomposes, as will hay or straw. Use a thermometer to track the temperature inside and if the plants are in danger of freezing, place blankets over the cover as an extra layer of insulation. Snow works remarkably well as an insulator, too, and chances are that will be available.

Plants in cold frames are in more danger of overheating than freezing, however. Set up the cover so that it can be propped open for ventilation or hinged up to allow it to cool. Old windows, shower doors or a sheet of Plexiglas can serve as the cover. Check the resale shops for materials. Try to find something that is shatter resistant, though. Thinner single-pane windows can crack or be smashed by debris and then you’re cleaning glass shards out of the broccoli.

Hoop frames or hoop beds are another option for extending the growing season, or dare I say it, creating a four-season harvest. As with cold frames, there are a few options for designing these. The basic concept is to use flexible piping like PVC to create a u-shaped frame that semi-transparent cloth or transparent thick plastic can be attached to. Like a greenhouse or cold frame, it will trap heat inside during the cooler months. The frame can be attached to a raised bed and same as above, the plants can be sowed directly into the ground or it can be filled with layers of organic matter to create a planting material.

Greenhouses are the least do-it-yourself option, but if you’ve got a bigger budget, they can be purchased and installed in the yard or assembled from a kit. A greenhouse could have possibilities beyond an extended growing season since the climate can be controlled more precisely. Exotic flowers could be gracing the windowsills, instead.

Planting choices for cold frames or hoop beds include all the cool weather vegetables such as broccoli, spinach, cabbage, kale, beets, radishes and varieties of greens. In our hardiness zone, these won’t last much into October and can’t be sown earlier than mid-April, depending on the specific vegetable. Once we get a decent melt of some of this snow, though, you could be planting in your new cold frame in March. There are many designs and specific instructions on building these projects available online. Let a Google search be your guide.