Cold frames act as mini-greenhouses that fit on top of our raised beds or can be placed directly on the ground. A single layer of glass creates a microclimate in which the nighttime temperature inside the frame can be as much as 20° warmer than the temperature outside, although the average difference is 7° to 10°F The daytime temperature inside the frame, even on a cloudy, early spring day, will be 10° to 15OF warmer than outdoors. Utilizing the earth’s insulating powers by sinking the cold frame into the ground will also aid in protecting the delicate crops.
The booster frames should be the same length and width as the main frame, but without tapered sides. By September, with biennials planted out, the cold frame can become home to autumn-sown hardy annuals which will happily overwinter here. In very cold winters, place old blankets, bubble wrap or layers of newspaper on top of the lid overnight. Seeds of many plants can be sown directly in the frame and grown there until it’s time to transplant them to the garden. The best thing I’ve found for propping the windows up is a 2” x4” scrap sawn to 6” long.
Cold frames are an easy way to speed up the process of Mother Nature by growing veggies in a protected and warmer climate than the outside environment would normally allow. If temperatures are going to plunge into the 20s F, your plants will be in trouble. If ground-level basement windows are present, it may be possible to build the frame outside such a window, which, when open, would provide some supplemental heat from the heated basement. I started with three small cold frames using windows set over boxes and was so pleased to have a little bit of fresh lettuce during the winter that I tried two low tunnels last year.
I keep a 4-foot board at the edge of the cold frame, which is used to hold up one edge while working in the cold frame. Expert advice from Jackie Whittaker, garden writer for Garden News – A cold frame can open a new dimension in gardening, giving the benefits of a longer season, enabling you to grow earlier, later, bigger and better crops, as well as raising more of your own flowers and shrubs.
And since the windows are not attached they can be lifted right off for storage. So the window sits on top of the wooden frame on three sides, up against the back board. Then in the fall, when the early frosts drop in on us, we can turn again to the lowly cold frame to protect those peppers or melons a few more days, or weeks, or maybe even another month. For many years we had a permanent cold frame gardening setup constructed of discarded windows, old cement blocks (back and front walls) and scrap boards (side walls and on top of the cement blocks.) In this, we started all of our seedlings.
Cold frames are great places to plant greens in late summer and hold them well past the first frosts of fall … and maybe longer. You’ll start to get a feel for how warm or cool your cold frame stays as time goes on. The corner posts are cut the same length as the width of the booster frame’s sides, but shifted upwards 1/4″ during installation, creating an extended locking post on top to mesh with the frame above, and a pocket underneath for locking onto frames below. Access Cold Frames come in a large range of sizes and shapes and are suitable for any size of garden, be it large or small.
After you build your structure, cover the floor of the cold frame with 3 to 4 inches of sand. In the old days, lights were 4 to 6 feet square and made of overlapping panes of glass. It would also be useful like that for keeping vine borer moths off of young squash plants. When choosing a cold frame, make sure the lid can be propped open for good ventilation during the day.
A good rule of thumb is to make your frame slope one inch for every 12 inches that it is deep; so if the frame is 4 feet deep from front to back, the back should be 4 inches higher than the front. Its basic parts are: ribs, which provide the framework of the house; stakes or ground pipes to secure the ribs to the ground; and plastic sheeting that stretches over the ribs and provides shelter to the plants inside. These savvy gardeners started salad greens (left) in their cold frame in early spring.
Although temporary frames may be set on the soil surface, excavation is required for more permanent structures. By far, the best role for your cold frame is to give you an extra-early head start on growing plants for the coming gardening season. We did have the advantage, if you can call it that, of the Gypsy Moth defoliation of our trees in the early summer causing the canopy above the cold frame to be less dense, to say the least – not something to wish for, or count on.
Just before building your cold frame, select a location that receives sunlight for most of the day. Hot beds are useful for seedlings that require constantly warm soil temperatures to germinate. The rate that plants grow diminishes with the shortening days of fall until it almost stops. Once seeds have germinated, temperatures should be adjusted for the type of plants involved.