By Contributing Editor Kristina Strain
Got a green thumb? Check out more articles in our Sustainable Yard & Garden Guide.
Ask any octogenarian farm kid about cold frames, and chances are they’ll nod with recognition. Small and easily constructed cousin to a greenhouse, cold frames are simply good sense. They allow an early jump on the growing season in spring, and can keep a household in green leafy vegetables until Christmas or longer with good management. In the hottest days of high summer, a cold frame can even double as a solar dryer: add a piece of screening and a few handfuls of blueberries, grapes, or currants, and you’ll have dried fruit to store for the winter. If you have a tiny scrap of sunny yard or flower bed, or even a south-facing patio or fire escape, a cold frame will make a welcome and productive addition to your home.
In this article, you’ll find a thorough description of the whens, wheres, hows, and whys of cold frames. At the bottom of this page, there’s a link to a simple tutorial on building a cold frame from salvaged materials. Additionally, cold frames, and similar season-extending products, are available in the Grow and Make store here.
Why a Cold Frame?
Instead of relying on refrigerator-trucked lettuces from across the country in March, imagine bringing in a bowlful of your homegrown tender spring mix. Apart from the obvious aesthetic and gustatory pleasures, growing a little of your own produce has great ecological benefits as well. Every food dollar spent on far-flung grocery store produce is a dollar spent endorsing petroleum. It’s not pleasant, but it’s true. The good news is, even without space for a garden, you can set up a cold frame and grow some things yourself. Unplug yourself from the petroleum pipe, get some fresh air and flaunt your independent and self-sufficient skills.
For folks who already have a garden, I’ve found that a cold frame is an easy, durable, and efficient way to extend the happy season of fresh homegrown vegetables by a few precious months. Smaller and simpler than a greenhouse, a cold frame can easily be constructed at home. In spring, it’s a fine place to start early greens or seedlings. In autumn, fill the cold frame with kale or chard and it will continue producing at least until Christmas.
Where to put a Cold Frame?
For the best results, and the most season-extending potential, locate your cold frame in a sunny spot. I have mine tucked against our house’s foundation, on the south side. As early as late February, the soil inside it is thawed and ready to plant. For city-dwellers, soil isn’t a pre-requirement. Even if all you have is a fire escape or tiny patio, your cold frame can grow flowerpots planted with lettuce seeds. The size and height of your apartment building will contribute some warmth and shelter to your crops, as well.
When to use a Cold Frame?
In Spring. As mentioned above, I usually get my cold frame underway in late February or early March. I start with hardy, cold-tolerant crops such as lettuces, spinach, arugula, chard, scallions, or cilantro. If the seed packet says, “plant as soon as the ground can be worked,” it’s fair game for early cold frame growing. With a few rows of lettuce in my frame, I’ve had the pleasure of serving homegrown produce to guests in mid-April. I keep the lid closed on blustery days and nights, but as the season progresses I’ll start opening the lid on particularly warm or sunny days. It’s amazing how hot it can under the lid when it’s in the sun!
In Summer. With the heat and sunshine of early summer, the cold frame crops begin to look hoary and ragged. At this point, there are two options: use the cold frame for some tender, heat-loving crops (such as peppers, cucumbers, or melons) or temporarily convert the cold frame into a solar dryer. By fitting a piece of screening (I use an old window screen) into the cold frame, and keeping the lid closed, one can successfully dry small fruits or low-moisture veggies. Anything that can be dried whole is fair game, as these are less susceptible to mold. If you live in a particularly hot or dry climate, other items might be possible as well. Take the items out of the cold frame when they’re leathery and shriveled, and store in tightly closed plastic baggies or small jars for the winter.
In Autumn. As the summer winds down, I make sure to plant a few rows of hardy fall crops in my cold frame. Kale, chard, broccoli, cabbage, and root crops are all good choices. Once the shivery cold days of November hit, I’ll begin keeping the lid closed again, as in the spring, keeping my crops sheltered from sub-freezing temperatures. Picking a few leaves of kale here, a handful of beets there, I can continue my homegrown harvest right into the icy heart of winter. Come January, I’ll close up shop for a few months before starting back up again in the spring. Dig in a few shovelfuls of compost to replenish the soil, and my frame is ready to go for a fresh season.