Greenhouses are used to create an ideal environment for plant growth. If an controlled environmental meets the needs of a crop, then it can be produced for specific markets as well as eliminate many of the variables that may alter or reduce plant growth. Temperatures can be regulated within a desired range, wind and precipitation are evaded, insect and disease damaged is reduced to tolerable level, as well as soil, water, and nutrient levels can be adjusted to meet the needs of plants.
A greenhouse or propagation unit is a structure covered with transparent material that utilizes sun light to grow plants. Greenhouses have heating, ventilating, and cooling equipment for temperature control. Conservatories are greenhouses in which collections of plants are grown for display. Their form may be more elaborate than commercial greenhouse types. On the other hand, cold frames or hotbeds are low structures fitted with removable glass or plastic covers. Plants grown in cold frames are maintained from outside the structure.
There are three types of greenhouses: (1) the lean-to greenhouse, (2) the detached greenhouse, and (3) the ridge and furrow greenhouse. The lean-to greenhouse slopes in one direction and is attached at the ridge to a building or another greenhouse. The detached greenhouse is a freestanding greenhouse that may be constructed in many styles. It may be connected to other greenhouses by a corridor or attached at one end to a workroom building. It is an even-span greenhouse if the rafters are of equal length; an uneven-span greenhouse if the rafters of one roof slope are longer than the rafters of the other roof slope. A ridge and furrow greenhouse consists of several greenhouses connected at the eaves. A gutter replaces the eave plates where two houses are joined. The internal walls beneath the gutters are generally omitted in contemporary ridge and furrow houses. If internal vertical walls are constructed, the houses making up a ridge and furrow greenhouse are known as contiguous houses. The standard ridge and furrow greenhouses is generally wider, has longer rafters, and is glazed with several overlapping panes of glass compared to other greenhouses.