Are you as impatient as I am, waiting for the frost-free planting dates to arrive? As the days get longer and spring inches closer, it’s hard not to get itchy fingers for gardening. Still, at this time of year, many of us need to wait for several more weeks, or even months, before we can start planting outdoors. But what if you didn’t have to wait that long? What if you could start gardening about five weeks prior to your traditional frost-free date? You can do it with a cold frame.
A cold frame is basically just a low bottomless box with a translucent top. It protects plants from the elements and provides solar heat to keep them warm.
Creating a Cold Frame
Cold frames are easy to build with found or repurposed items, and unless you want to, there is no need to use tools. It’s true that they’re often built from lumber, with distinctive sloping tops that are covered with clear poly sheeting, polycarbonate sheets or glass. It’s easy to find plans for these kinds of cold frames, like or . If you are recycling windows or other material to use as the lid, you can certainly modify the plans to fit the dimensions of the cover.
If you’re not handy with tools, don’t despair. Start by finding something that will work as the translucent cover, so that you know how large the frame should be. To create the frame itself, you can use things like straw or hay bales, cinder blocks, or bricks.
Although having a sloping lid is ideal, as it captures more sunlight and facilitates rain runoff, it’s not necessary. The cover can just rest flat on top of the frame. Make sure the lid fits well, though. To best protect the plants, there shouldn’t be any gaps between the cover and the frame. A well-fitted lid will also increase the humidity levels, which will keep your plants happy.
Choosing a Location
The weeks prior to your last frost date can be nippy. To keep your plants toasty and flourishing, position the frame so that it faces due south and gets full sun.
Traditionally, seeds are planted right in the ground inside the frame. However, the frame can also be used as a mini-greenhouse, if you prefer, where you can start seeds in trays or pots for later transplanting. In this case, the frame even could be placed on a deck or patio if necessary, but take care to protect the area underneath.
Best Plants for Cold Frames
Cold frames are widely used to grow lettuce, which are cool-weather crops that flourish in temperatures of 45 to 75 degrees Fahrenheit. Other greens work well, too, such as beet greens, chard, kale and spinach. If you want to branch out from leafy greens, give carrots, leeks, radishes, kohlrabi or turnips a try.
Managing the Temperature
Cold frames are easy to build with found or repurposed items, and unless you want to, there is no need to use tools. It’s true that they’re often built from lumber, with distinctive sloping tops that are covered with clear poly sheeting, polycarbonate sheets or glass. It’s easy to find plans for these kinds of cold frames, like this one at Better Homes and Gardens or this one at Popular Mechanics. If you are recycling windows or other material to use as the lid, you can certainly modify the plans to fit the dimensions of the cover.
If the outdoor temperature is consistently lower than 40 degrees, insulate your frame by heaping soil or mulching materials like leaves or wood chips around its perimeter.
Using Your Cold Frame Beyond Spring
Although most commonly used to start vegetables early in the spring, a cold frame can be used year-round. It provides a good home to heat-loving vegetables like peppers and eggplants until the extreme heat of summer hits. During the hottest days of summer, simply remove the lid to keep using the space. The fall growing season can be extended by replacing the cover at that time. Frames also can be used to overwinter plants.
For the minimal cost and effort needed to build them, cold frames provide a big payoff.
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