If the cold temperatures a few weeks ago damaged your garden
plants, perhaps it’s time for you to build a cold frame. Because the runners of a nearby blackberry
bush scurried under the base of the cold frame and sprouted a new plant inside
the open box, and I procrastinated about removing it, I managed to plant my
cold frame just before the recent cold snap.
However, the protective environment of the cold frame will cause the
seeds to germinate, and I’ll soon have happy lettuces and spinach for the rest
of the winter.
Unless snow falls or the temperature remains below freezing
all day, which rarely happens here in SC, I open the cover of the cold frame every
morning. Winter vegetables do not enjoy
temperatures much above 70°F; think
about how easily your car heats to that temperature and beyond on an otherwise
chilly day if it’s parked in the sun.
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| My cold frame |
My husband and I made my cold frame, which is a box covered
with glass, with a discarded shower door.
Any glass or Plexiglas door or window would work; the glass allows sunshine
and heat to reach the plants inside the cold frame. If you were going to open the lid daily to
allow sunlight to reach the plants, even an opaque lid would work. The plants will be fine in the shade for a
day or two if very cold weather threatens.
After you raise the lid, make sure to attach it to the ground in some
way so that strong gusts of wind do not suddenly close it and shatter the
glass.
We made the sides of my cold frame out of treated
lumber. We caulked the joints and put
some weather-stripping along the top of the frame to prevent drafts. The back of the cold frame is about 18 inches
high, and it slopes down to the front at about a 40-degree angle toward the
southern sky; the front is about 8 inches high.
This slope is supposed to maximize the amount of captured sunlight.
If carpentry is not your forte, use stacked hay bales,
concrete blocks, or landscape timbers. My
mother surrounded some of her vulnerable plants with black plastic bags full of
leaves and found they provided sufficient insulation to protect them from much
damage, especially if she draped a sheet of plastic over the top of the circle
of bags. Plug as many cracks as you can.
Place your cold frame directly on the ground, fill your cold
frame with compost-enriched soil, and plant the seeds or transplants. Because of the greenhouse-like moist
environment, seeds sprout quickly and are the most economical choice. Water the soil when it begins to dry out and
fertilize the plants as you would in your garden.
The best plants for a cold frame are lettuces, spinach,
collards, and other cool-season greens.
Carrots, beets, and parsnips also like the protected environment. Depending on your cold frame’s interior
height, you might also be able to grow broccoli, cauliflower, and cabbage. This winter, I am growing broccoli inside a
cold frame without a lid, because it shattered in a wind gust, and I am
protecting them with a sheet of plastic.
Gardening supply companies carry prefabricated cold frames; harvesting
your own salad greens instead of buying them will offset the purchase price
quickly.