Sentence:  Tomato seedlings will be ready to transplant from the <WSD>hotbed</WSD> to the coldframe in 12 to 18 days after sowing the seed, depending upon the amount of sunshine and the care given the bed. 
Meaning of the word marked with <WSD> tags:  A low bed of earth covered with glass, and heated with rotting manure, used for the germination of seeds and the growth of tender plants, like a miniature hothouse.