A greenhouse, made of either glass or plastic, is used for the cultivation and protection of plants that might be delicate or plants that are grown out of season. Crop Growth [Courtesy of NASA] The design of a greenhouse allows for the control and balance of temperature, moisture, and light to suit the growth requirements for many diverse plants including some foods. Natural sunlight in the particular temperature region is usually sufficient to meet the light requirements of plants in spring and fall but in winter light is supplemented by artificial light to help with the growing process. The same type of process, the use of artificial light, would have to be used to grow particular foods on board a Wheat Crop [Courtesy of NASA] spaceship, like ISS, for example. When the sun's heat is not being used in the winter, enriched heat comes from steam, hot water, or hot-air circulating systems. During the hotter months, whitewashing the panes or blowing air through with fans reduces heat.