A greenhouse (also called a glasshouse ) is a building where plants are cultivated.
A greenhouse is a structure with a glass or plastic roof and frequently glass or plastic walls; it heats up because incoming solar radiation from the sun warms plants, soil, and other things inside the building faster than heat can escape the structure. Air warmed by the heat from hot interior surfaces is retained in the building by the roof and wall. These structures range in size from small sheds to very large buildings.
Greenhouses can be divided into glass greenhouses and plastic greenhouses. Plastics mostly used are PEfilm and multiwall sheet in PC or PMMA. Commercial glass greenhouses are often high tech production facilities for vegetables or flowers. The glass greenhouses are filled with equipment like screening installations, heating, cooling, lighting and may be automatically controlled by a computer.
The glass used for a greenhouse works barrier to air and its effect is to trap energy within the greenhouse, which heats both the plants and the ground inside it. This warms the air near the ground, and this air is prevented from rising and flowing away. This can be demonstrated by opening a small window near the roof of a greenhouse: the temperature drops considerably. This principle is the basis of the autovent automatic cooling system. A miniature greenhouse is known as a cold frame.
Uses
Greenhouses protect crops from too much heat or cold, shield plants from dust storms and blizzards, and help to keep out pests. Light and temperature control allows greenhouses to turn inarable land into arable land, thereby improving food production in marginal environments.
Because greenhouses allow certain crops to be grown throughout the year, greenhouses are increasingly important in the food supply of high latitude countries. One of the largest greenhouse complexes in the world is in Almeria, Spain, where greenhouses cover almost 50,000 acres (200 km 2 ).
Greenhouses are often used for growing flowers, vegetables, fruits, and tobacco plants. Bumblebees are the pollinators of choice for most greenhouse pollination, although other types of bees have been used, as well as artificial pollination. Hydroponics can be used in greenhouses as well to make the most use of the interior space.
Besides tobacco, many vegetables and flowers are grown in greenhouses in late winter and early spring, and then transplanted outside as the weather warms. Started plants are usually available for gardeners in farmers' markets at transplanting time. Special greenhouse varieties of certain crops such as tomatoes are generally used for commercial production.
The closed environment of a greenhouse has its own unique requirements, compared with outdoor production. Pests and diseases, and extremes of heat and humidity, have to be controlled, and irrigation is necessary to provide water. Significant inputs of heat and light may be required, particularly with winter production of warm-weather vegetables.
Because the temperature and humidity of greenhouses must be constantly monitored to ensure optimal conditions, a wireless sensor network can be used to gather data remotely. The data is transmitted to a control location and used to control heating, cooling, and irrigation systems.
In addition to growing and displaying plants, greenhouses, at least in the in the United States, are also widely used as areas where the public buys plants from. Frequently, the same greenhouse where the plant is grown, is the one where the public shops from and purchases in.
Biologist John Todd invented a greenhouse that turns sewage into water, through the natural processes of bacteria, plants, and animals.
An agricultural pioneer known as Pete Johnson has recently become a successful pioneer in the use of movable greenhouses in farming.
History
The idea of growing plants in environmentally controlled areas has existed since Roman times. The Roman emperor Tiberius ate a cucumber-like vegetable daily. The Roman gardeners used artificial methods (similar to the greenhouse system) of growing to have it available for his table every day of the year. Cucumbers were planted in wheeled carts which were put in the sun daily, then taken inside to keep them warm at night. The cucumbers were stored under frames or in cucumber houses glazed with either oiled cloth known as "specularia" or with sheets of mica, according to the description by Pliny the Elder.
The first modern greenhouses were built in Italy in the thirteenth century to house the exotic plants that explorers brought back from the tropics. They were originally called giardini botanici (botanical gardens). The concept of greenhouses soon spread to the Netherlands and then England, along with the plants. Some of these early attempts required enormous amounts of work to close up at night or to winterize. There were serious problems with providing adequate and balanced heat in these early greenhouses.
Charles Lucien Bonaparte, a French botanist, is often credited with building the first practical modern greenhouse in Leiden, Holland to grow medicinal tropical plants.
Originally on the estates of the rich, with the growth of the science of botany greenhouses spread to the universities. The French called their first greenhouses orangeries , since they were used to protect orange trees from freezing. As pineapples became popular pineries , or pineapple pits, were built. Experimentation with the design of greenhouses continued during the Seventeenth Century in Europe as technology produced better glass and construction techniques improved. The greenhouse at the Palace of Versailles was an example of their size and elaborateness; it was more than 500 feet long, 42 feet wide, and 45 feet high.
In the nineteenth Century the largest greenhouses were built. The conservatory at Kew Gardens in England is a prime example of the Victorian greenhouse. Although intended for both horticultural and non-horticultural exhibition these included London's Crystal Palace, the New York Crystal Palace and Munich’s Glaspalast. Joseph Paxton, who had experimented with glass and iron in the creation of large greenhouses as the head gardener at Chatsworth, in Derbyshire, working for the Duke of Devonshire, designed and built the first, London's Crystal Palace. A major architectural achievement in monumental greenhouse building were the Royal Greenhouses of Laeken (1874-1895) for King Leopold II of Belgium.
In Japan, the first greenhouse was built in 1880 by Samuel Cocking, a British merchant who exported herbs.
In the Twentieth Century the geodesic dome was added to the many types of greenhouses. A notable example is the Eden Project, in Cornwall.
Greenhouse structures adapted in the 1960s when wider sheets of polyethylene film became widely available. Hoop houses were made by several companies and were also frequently made by the growers themselves. Constructed out of aluminum extrusions, special galvanized steel tubing, or even just lengths of steel or PVC water pipe, construction costs were greatly reduced. This meant many more greenhouses on smaller farms and garden centers. Polyethylene film durability increased greatly when more effective inhibitors were developed and added in the 1970s. These UV inhibitors extended the usable life of the film from one or two years up to 3 and eventually 4 or more years.
Gutter connected greenhouses became more prevalent in the 1980s and 1990s. These greenhouses have two or more bays connected by a common wall, or row of support posts. Heating inputs were reduced as the ratio of floor area to roof area was increased substantially. Gutter connected greenhouses are now commonly used both in production and in situations where plants are grown and sold to the public as well. Gutter connected greenhouses are commonly covered with a double layer of polyethylene film with air blown between to provide increased heating efficiencies, or structured polycarbonate materials.
Shadehouse
A shadehouse serves the opposite purpose of a greenhouse; it is used to protect cultivated plants from excessive heat, light or dryness.
Gallery
See also
- Bioshelter
- Biosphere 2
- Conservatory (greenhouse)
- Greenhouse effect
- Lord & Burnham (greenhouse manufacturers)
- Royal Greenhouses of Laeken in Belgium
- Seasonal thermal store
- The Eden Project
- USDA
- Vertical farming
References
Notes
- ^ Plants Profile for Victoria amazonica, USDA Plants Database
- ^ Banner Engineering (November 2009), Application Notes , http://www.bannerengineering.com/en-US/wireless/surecross_web_appnotes
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