Greenhouse

A greenhouse is a building made of glass or plastic for the purpose of growing plants. The glass selectively transmits specific frequencies of light. The sun's irradiation warms the plants, soil, and beds inside the building. Air warmed by the heat from those interior surfaces is retained by the roof and wall and circulated, if necessary, by fans.Because it is a closed system, everything needed by the plant must be provided by the grower. Irrigation systems deliver water, and pollination is usually effected by importing bumblebees. A close watch must be kept for pests and diseases, and the temperature must be carefully controlled. A drop in temperature, for example, may be countered by pumping steam into the greenhouse.Commercial greenhouses may be used to start seedlings that are later planted outdoors, either by farmers or in home gardens. Tobacco, flowers, and vegetables, especially tomatoes, may be grown entirely in greenhouses, especially in colder climates. A hydroponic system may be used to conserve space. The largest greenhouse complex in the world is in Ontario, where there are 200 acres of tomatoes growing under glass.Home greenhouses are a great boon to the gardener, providing an early start for seedlings and allowing an extended season for flowers. They can be as small as a four-by-four-foot box with a glass cover or a building large enough to walk around in. Greenhouses are a fairly easy project for do-it-yourselfers, and a greenhouse kit can make building a terrarium even easier.