Section 2: Common Types Controlled Environments Used in Horticulture
There are various types of structures that are used in controlled environment horticultural crops production. The structures and types of control systems that are used are dictated by which of the environmental factors must be controlled, to what degree they must be controlled, and the cost of controlling them in relation to the value of the crop(s) being produced. Each environmental parameter that must be controlled increases facility and production costs. The objective is to design a controlled environment structure that allows for the control of those parameters that need to be controlled at the level of precision required. Doing more only adds to the cost of production. Common types of controlled environments include:
Hoop Houses
A true hoop house is generally only an arched structure or frame that provides cover, and thus some degree of light and temperature control for crops. Hoop houses are generally used for over wintering plant materials or for starting hardy spring crops (broccoli, cabbage, ornamental perennials) early in the season. They typically do not have heating or cooling systems. Hoop houses may be covered with polyethylene film, shade fabric or may have no covering during warm seasons. Sometimes these structures are referred to as quonset houses. However, one type of common greenhouse design is the quonset-type structure. Therefore, the term quonset should be used only to refer to a type of greenhouse design.
High Tunnels
High tunnels have become popular controlled-environment structures for those growing fruits and vegetables. High tunnels are essentially the same as hoop houses but they are almost always covered with a single layer of polyethylene film and often have retractable side walls and ends that can be rolled up or down depending on the inside temperature and humidity. High tunnels are generally used to provide for temperature modification (as well as protection from wind and rain) to increase the season for small fruit and vegetable production. The temperature protection allows crops to either be started earlier in the season or grown later into the season than would normally be possible for a given location.
Cold Frames
Cold frames are similar to hoop houses and serve a similar purpose. The difference is that a cold frame may be partially set into the ground, is typically not as tall as a hoop house and may have a flat roof. The side walls of cold frames may be constructed of wood, concrete blocks or bricks. The top is usually made of some type of translucent material so the light can enter the structure. The roof is also usually hinged on one side the that the roof section may be lifted to open the cold frame. Cold frames are generally used for over-wintering plant materials or for starting hardy spring crops (i.e. broccoli, cabbage, ornamental perennials) early in the season. Cold frames may also be used to provide the necessary cold treatments to bulb crops. Cold frames have no heating or cooling systems.
Hot Beds
Hot beds are similar to cold frames except that hot beds have some type of heat source and thus provide more control over temperature. The heat source may be hot water or steam from a boiler, electrical heating units, incandescent light bulbs or composting manures placed inside of the hot bed. Hot beds are most often used for starting plant materials in the early spring.
Shade Houses
Shade houses (sometimes referred to as saran houses) are structures that are covered with a fabric made of polypropylene, cotton, plastic or other material that is designed to partially exclude light. Some shading materials are aluminized so that light is actually reflected away from the structure. The cover material may be selected to block out varying amounts of light, but typically shading materials excluding 20% to 60% of the incoming light are most common. These structures are generally used in mediterranean, subtropical (i.e. Florida, southern Texas, southern California) and tropical climates where reducing the light level and providing some measure of cooling (by shading) is desired. If the shade fabric is extended down the sides of the structure to the ground, crops inside of the structure are also partially protected from wind. Shade houses typically do not have heating or cooling systems. Shade houses are most often used in the production of cut flowers, foliage plants and nursery stock.
Coolers
Coolers allow for plant materials (i.e. bulbs, seed, plants) to be held at low temperatures. Typically temperatures in the range of 35 - 50° F (2° - 10° C) are most common. In a few situations, temperatures below 32° F (0° C) may be required (i.e. freezing in of bulbs). Coolers are most often used for the storage of vegetables, fruits and cut flowers, holding nursery stock and providing a cold treatment (for vernalization or to break dormancy) to bulb crops.
Growth Chambers
Growth chambers are computer-controlled enclosed units that potentially allow for very precise control of many or all of the environmental parameters previously discussed. Growth chambers are most often used for research purposes although they may be used in some propagation situations such as tissue culture. Growth Chambers may be small reach-in chambers or large walk-in chambers.
Germination Chambers
Germination chambers are similar to walk-in growth chambers except that they primarily allow for the control of temperature, humidity and possibly light. They are often large walk-in rooms that are well insulated to minimize temperature fluctuations, and they have some type of fog system used to maintain a high relative humidity. They are designed specifically to provide an optimal environment for seed germination with minimal fluctuations in temperature and relative humidity.
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Greenhouses
Greenhouses are the most common types of structures used for production of ornamental and vegetable crops under controlled environments. Greenhouses provide the potential to control all environmental parameters, although to varying degrees depending upon the design of the greenhouse and the types of control systems utilized. The remainder of this learning unit and future learning units will focus specifically on greenhouse structures and the production of crops in greenhouses.
