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greenhouse,enclosed glass house used for growing plants in regulated temperatures, humidity, and ventilation. A greenhouse can range from a small room carrying a few plants over the winter, to an immense heated glass building called a hothouse or conservatory, covering acres of ground and used for forcing fruits or flowers out of season. Greenhouses have long been used for holding plants over cold seasons and for growing tropical plants and less hardy fruits, but only in this century has the greenhouse been used for forcing vegetables. Now millions of dollars' worth of plant products are raised yearly in greenhouses. See cold framecold frame,
in horticulture, sun-heated board frame covered with a removable top of glass or other transparent material and sunk into the ground. The top may be solid or slatted or screened for shade.
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See A. Laurie et al., Commercial Flower Forcing (6th ed. 1958); H. Ibbotson, Build Your Own Greenhouse (rev. ed. 1965); H. T. and R. T. Northen, Greenhouse Gardening (2d ed. 1973).
a well-ventilated building with glass walls and a glass roof in which experiments on plants are conducted.
In a greenhouse pots containing plants are placed in carts. During the day in good weather the carts are rolled out to a patio adjoining the greenhouse on the south side or to a fenced-in pavilion (for protection from birds) not far from the greenhouse. In Russia the first greenhouse was built on the initiative of K. A. Timiriazev in 1872 on the grounds of the Petrovskoe Agricultural Academy (now the Timiriazev Moscow Agricultural Academy).
a glass structure for growing southern trees and shrubs that cannot endure the climate of a given locality, particularly in the winter. Most often grown are evergreens (for example, palms), citrus plants (lemon, orange), fruit and berry plants, and flowering plants. Plants raised in greenhouses during the summer include those that require special conditions of temperature, light, and air. Solar, steam, water, electrical, or hot-air heating is used to maintain the necessary temperature (1°C and higher). There are cool (1°–8°C), warm-temperate (8°–15°C), and tropical (15°–26°C) greenhouses. One form of greenhouse is the lean-to, in which the roof has a single slope, facing southward with an angle of inclination of 30°–45°. Another type, the even-span greenhouse, has a two-sloped roof, with internal supports. The slopes face west and east and have an angle of inclination of 24°–28°. Sometimes two to five or more even-span greenhouses are combined into one or are connected to each other by chutes supported from the bottom. There is also a greenhouse in the even-span style that does not have internal supports. In some greenhouses the plants are set in benches, in others the plants are raised directly in the ground. Sometimes both methods are employed. Winter greenhouses have permanent glass and are used year-round; spring greenhouses have removable frames or a completely open roof.
The foundation of a greenhouse is made of brick, stone, or wood, and the floor is earthen. The single frames are made of wood or metal, and double-thick glass is used (thickness, 2.7–3.3 or to 4–5 mm). Ventilation is achieved by means of air vents, fanlights, or individual detachable frames. In large greenhouses, a water supply line and a device for pouring warm water are constructed; sprinkling or subsoil irrigation is used. In industrial greenhouses, the basic agricultural work (soil cultivation, sowing, planting, plant maintenance, control of pests and plant diseases) is done with farm machines and implements. Loads are transported inside the greenhouse by rail and on small trucks.
A greenhouse should be constructed so that it permits the least heat transfer per sq m of useful area, maximally receives and uses the light and heat from natural sources, regulates the temperature and the moisture content of the air and soil, permits the mechanization of labor, and yields maximum production with minimum running costs.
Many large greenhouses are used for industrial (growing early vegetables and fruits, cultivating ornamentals) and scientific purposes.
REFERENCESAdoratskii, V. V. Osnovy teorii teplichnykh sooruzhenii (Krupnye teplichnye khoziaistva s tochki zreniia promyshlennoi arkhitektury). Moscow, 1939.
Klang, I. I. Oranzherei i parniki ν dekorativnom sadovodstve. Moscow-Leningrad, 1950.