A cold frame with an added heat source becomes a hotbed. By heating the soil in beds, you can speed up the seed germination of most vegetables. The seeds of cool-season crops sprout eagerly at soil temper atures as low as 50° F. Seeds of warm-season crops 'sulk' and rot when soil temperatures remain below 65 degrees. Within these two categories, each vegetable has its own temperature requirements for seed germination. (See Figure 6.14 for seed germination temperatures of commonly grown vegetables.)
The most efficient methods of heating are by cable or mats. Most come with a built-in thermostat that makes it easy to monitor the soil temperature and keep it constant To install cable in a bed, lay the cable out on the ground within the frame and spread it evenly over the entire area in large loops. Cover the cable with 2 to 3 inches of sand and then with 3 to 6 inches of garden soil.
To heat the frame naturally, place it on top of a pit containing about 18 inches of green organic material (grass clippings or other vegetation) or fresh manure, The bacterial action involved in the rotting of the material will supply heat to the frame. You can also heat a frame by placing one or more light bulbs in the box. This is not a particularly efficient method, but it does work.
Was this article helpful?
Learn what you can do with herbs! How to Plant, Grow, and Cook with Natural Herbs. Have you always wanted an herb garden but didn't know how to get started? Do you want to know more about growing your own herbs in the privacy of your home and using them in a variety of cooking?