hotbed

hotbed low, glass-covered frame structure for starting tender plants. It differs from a cold frame only in that the soil is heated—either artificially as by underground electric wiring or steampipes, or naturally with partially fermented stable manure, which is mixed with dead leaves or straw, placed in the bottom of the hotbed frame, and covered with a layer of soil. Heat is produced by the decaying organic matter. Proper ventilation is important, as is thermostatic control of artificially heated hotbeds. Tomatoes, cucumbers, celery, and other crops can be grown in hotbeds in the spring.

hot·bed / ˈhätˌbed/ • n. a bed of earth heated by fermenting manure, for raising or forcing plants. ∎  an environment promoting the growth of something, esp. something unwelcome: the country was a hotbed of revolt and dissension.