Manure and electric heating cables are the most common heat sources. The advantage of manure as a heat source is its low cost. Disadvantages include cleaning out the used manure each year, odors, the inability to precisely regulate the temperature, and the need to replace the manure each year. Electric heat sources are more expensive to install and operate but can be reused for several years. Spread four inches of coarse gravel on the bottom to help drainage and aeration.
Warm soil permits faster heating and speeds germination.
Place a thermometer in the soil. As the manure decomposes, heat is released. Electrically-heated Hotbed An easier approach to heating a hotbed is to use electric cables. About 60' of lead or plastic covered electric heating cable is needed for a 6' x 6' bed or about 2' of cable for every square foot of bed. Be sure that the bed is properly wired for safe operation.