Greenhouse
A greenhouse is a specialized structure designed to protect delicate plants from harsh weather while promoting optimal growth conditions. These buildings have a rich history, with evidence of their use dating back to ancient civilizations, including the Egyptians, who cultivated grapes in early greenhouses as far back as 4000 BCE. Greenhouses are utilized for both commercial agriculture and personal gardening, varying greatly in size from expansive facilities to small backyard structures. They primarily consist of materials that allow sunlight to enter, such as glass or polyethylene, which help create a warmer internal environment through the greenhouse effect.
Modern greenhouses often include sophisticated monitoring and control systems to maintain ideal growing conditions, featuring thermostats, irrigation systems, and sometimes even automated energy curtains to regulate light and temperature. Various designs exist, including even-span and hoop houses, each serving specific gardening needs. Additionally, significant historical developments in greenhouse technology, such as the use of underfloor heating systems and the design advancements in the seventeenth century, have greatly enhanced plant cultivation practices. Overall, greenhouses play a crucial role in extending the growing season and enabling the cultivation of a wide variety of plant species.
Greenhouse
A greenhouse is a structure meant to protect tender plants from the elements. Greenhouses have an ancient history, and they are still used to produce food crops and flowers outside their normal growing seasons. They are similar to other structures, such as conservatories, which are rooms typically attached to houses that provide living spaces for both plants and people.
Greenhouses may be used for commercial purposes or private gardening. They may provide space for thousands of plants or just a few. Greenhouses may enclose several acres or less than a meter of land. Many public gardens include greenhouses, which may shelter rare or tender plant specimens or small groups of trees.
Background
Researchers have found some evidence of greenhouses used by ancient civilizations. Pictographs show Egyptians growing grapes in conservatories and greenhouses as early as 4000 BCE. One of the earliest known greenhouses was described by Lucius Junius Moderatus Columella and Gaius Plinius Secundus, known as Pliny the Elder. In the first century CE, they wrote about proto-greenhouses, or specularia, built for the Roman emperor Tiberius on the Isle of Capri. The beds in which plants were grown in these greenhouses were on wheeled carts. The beds were rolled outside when the weather was favorable and kept inside in winter. Tiberius was believed to have had these structures built specifically to grow a vegetable that he ate daily. This vegetable was originally thought to be cucumber, though researchers suspect it was really a type of melon grown in the area and that the cucumber confusion was the result of an incorrect translation of ancient texts.
Hypocausts, or underfloor heating systems used in conservatories and greenhouses, were invented during the first century BCE by an Italian named Caius Sergius Orata. Lucius Junius Moderatus Columella, who wrote about the Roman emperor's greenhouses, also described how to use mica (a translucent mineral) in structures to protect plants.
Greenhouses appeared again during the seventeenth century in Europe. Salomon de Caus, an engineer and garden designer, designed some structures to protect orange trees in the royal gardens in Heidelberg, Germany, around 1619. The greenhouses were designed to come apart, so they could be removed during the warm summer months and replaced to protect the tender plants during the cold season. These walls and roof pieces were mostly wood, with a few windows, according to records of the time. However, putting them up and taking them down proved to be so arduous that de Caus eventually advocated for building a permanent structure of stone to protect the plants.
Greenhouses were likely in use in other places, though little evidence remains. The first known greenhouse in England was constructed during the early- to mid-seventeenth century in Chelsea, London, in the Physic Garden of the Society of Apothecaries. Many British explorers returned from their adventures with exotic plant species, often from the warmer climates of Africa and Asia. Greenhouses became necessary to protect these treasures from England's elements.
Overview
A strictly utilitarian greenhouse generally includes several basic features. Foremost are the materials that let in light. These coverings, called glazing, may be glass, polyethylene, or structured sheets. Polyethylene, or poly, is the most common because it is very energy efficient. Two sheets are usually used, with a blower fan positioned to keep the sheets three to six inches apart. This air space serves as insulation. A tight-fitting poly house uses less fuel than a single glass roof structure, but it reduces light levels to between 75 and 80 percent. Humidity can also become trapped inside, which may increase the risk of fungal disease. Glass coverings transmit the most light, and they are durable. Structured sheets are made of acrylics, fiberglass, and polycarbonates. Polycarbonates, which are the most commonly used, form twin walls that look like corrugated cardboard. The hollow tubes between the walls provide insulation.
Modern greenhouses come in a variety of shapes and sizes. The framework must be strong but narrow to allow the greatest amount of light to enter. Aluminum is most often used for the framework, though galvanized steel and aluminum-steel combinations are also common. Even-span greenhouses look like traditional houses, with straight sides and pitched roofs. These may be lean-to greenhouses, which are attached to another building that provides some support to the structure. A hoop house looks like a half-barrel on its side. Bent tubular pipe provides the framework, which usually supports plastic. Hoop houses are often used as temporary or short-term growing structures because the plastic needs to be replace every three to four years. Structures can also be connected to create a larger growing space. The Eden Project, the world's largest greenhouse project, uses domed greenhouses made of hexagonal panels.
Most greenhouses include some monitoring systems. Thermostats may monitor the temperature inside and control a number of features—such as fans, heaters, and vents—to ensure plants do not get too hot or too cold. Electronic sensors and computerized control systems may also monitor growing conditions and adjust features accordingly with little human oversight required. Greenhouses may also include irrigation systems and supplemental lighting.
Energy and shade curtains can be automatically adjusted to reduce light levels during the day for some crops and to provide additional insulation at night. Short day curtains can automatically open and close to manipulate plant growth. For example, some plants, such as poinsettias and chrysanthemums, are triggered to flower when the days become shorter. Short day curtains create the ideal flowering conditions by blocking out light for prescribed hours of the day.
Some commercial growers use retractable roof greenhouses. The roofs can be completely opened or closed as weather conditions change. Crops can be grown on the floor, in beds, or on supports called benches.
Greenhouses may require heating systems. Steam heat has been commonly used in greenhouses, but the boiler systems required are large. Small commercial operations may instead install forced hot air heaters and fans throughout the structure. Infrared heaters in the peaks of a greenhouse can also transmit heat energy to the benches, floor, and soil, which transfer the heat to the air around the plants.
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