Building a hotbed/coldframe

Are you sick of gardening yet or would you like to get more out of it? The season is winding down in many areas of the country, but you can extend it by building a hotbed or cold frame.  It’s a box with a clear roof, and the plants are grown inside. The only difference is the source of heat. The sun supplies all the heat in a cold frame, and an insulated heating cable adds to the warmth in a hotbed. This mini-greenhouse can also be used to start your plants earlier in the spring. 

Larry Caplan is an extension horticulture educator at Purdue University. He says most frames are made out of wood, but you can build one from just about anything.

"Some people if they’re using wood, will use pressure-treated wood or wood that’s got some preservative on it. Others have gone with redwood or cedar, which is a little more resistant to rotting than just untreated wood. Other people have made use of bricks or cinder blocks," says Caplan."

You will also need some sort of clear material to cover the top.

"Glass has been used, but it doesn’t have a lot of good insulating qualities and it’s fairly fragile," he says. "But you can use Plexiglas, fiberglass, polyethylene, pretty much anything that is clear and reasonably sturdy. A lot of people will use old window frames because they have them. If they’re treated carefully, they should work fine."

The frame should have a southern exposure that’s protected from wind and out of the shade. It should be near a water supply, and an electrical outlet if you’re using it as a hotbed. It’s also a good idea to add a thermometer and a way to ventilate the box so the plants don’t overheat on a sunny day.