Now that we have had a couple of hard freezes, not much is growing in the garden. However, the cold hardy crops are holding well in the ground, and we are still harvesting. Last night I made a delicious vegetable stir fry with bak choy, kale, peppers (stored in the refrigerator since harvest), garlic, ginger and mushrooms, and only the mushrooms came from the market. With a little effort, I could have grown shiitakes, also. This veggie mélange made a great side for roast chicken.
The first coldframe we ever used, and one of the easiest to construct, was made out of half-inch PVC pipe. We build raised beds about 3 feet by 8 feet. Five ten-foot long pieces of PVC pipe and a roll of transparent polyethylene sheeting will convert such a bed into a coldframe for about $20. Simply stick the pipe in the soil on one side of the bed, bend it over and similarly push it into the soil on the other side, forming a half-hoop to support the plastic. Place one pipe hoop at each end, and space the others each about three feet in from the ends. You can also use exterior screws to attach the pipe to the bed frame. Use the fifth piece of pipe to reinforce the others by running along the top of the hoops to form a "roof peak." Cut this piece of pipe to the required length, and secure it with duct tape or zip ties. The entire structure will be sturdier as a result. When the PVC frame is in place, cover with the plastic, anchored down with rocks or other weights along the edges. Instant coldframe! This arrangement is easy to disassemble and store when warm weather returns, also. As a rule, 4 mil polyethylene sheeting will last only one winter. If you want a more durable covering, use 6 mil polyethylene, which is a bit more costly.
You often read about the need to open a cold frame on warm days. We have found that unless the foliage of the plants is touching the transparent parts of the cold frame, there is little reason to do this. Plus, warming the soil helps keep the plants warmer that night. You may need to experiment to determine if your cold frame needs ventilating.
Time to get our your notebooks and start planning next year's garden. The seed catalogs will be arriving soon. If you plan to start your own transplants, remember that some, like celery, celery root, artichokes and leeks, need to be started in January because they grow so slowly.