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Growing Orchids in a Greenhouse


A Classic Glass Greenhouse © 2008 Greg Allikas

Greenhouses run the gamut from elegant conservatories to compact window greenhouses that fit snugly into a kitchen window frame. Whatever the size, similar suggestions for selection, design and installation apply. There are three major types of greenhouses to consider. The lean-to greenhouse is usually small, about 6 to 10 feet long. One of its long sides is formed by the side of the house to which it is attached. Relatively inexpensive to make and maintain, its major drawbacks are a lack of space for an expanding collection and a tendency to heat up and cool off more rapidly than is desirable.

The attached greenhouse is an extension of one's home, connected at the narrow end rather than the long side, as with the lean-to greenhouse. It is generally large and thus capable of providing more reasonable control over humidity, ventilation and expansion problems. Some homeowners incorporate a living area into a lean-to or attached greenhouse.

The free-standing greenhouse is unattached on all four sides. It is the most expensive to construct but, aside from some inconvenience of access in inclement weather, it offers maximum light and the best control. Some space must be sacrificed for a work bench and storage area.

Visit as many orchid greenhouses as possible, and consult books on and manufacturers of greenhouses before making a final decision. Where space is limited inside the home, window greenhouses offer a prime space in which to cultivate small-growing orchids. Opt for a model with vents and small fans that enhance ventilation. Two or three shelves increase space; they may be solid, to prevent water from dripping on the plants below, or perforated to aid air circulation.

Size
The optimum size with which to begin is a greenhouse 14 feet wide and 14 to 20 feet long. This affords a center bench as well as two side benches. Such a greenhouse may seem enormous at first, and unnecessary for an initial collection, but there are several factors to consider. First, those contemplating a greenhouse are serious about orchid growing. Consequently, the collection will inevitably grow by leaps and bounds. What seems to be adequate space today will become a major limitation in two years. Second, since a large greenhouse is preferable in the long run, it is less expensive to build it now than to add an extension onto a smaller one in the future.

Light
Regardless of the type, locate the greenhouse to capture maximum light. The best position for a free-standing one is on a north-south axis so that the sun travels across the entire length as it moves from east to west. A lean-to or attached greenhouse should also have a maximum exposure, east or south, but never north. Avoid nearby shade trees or shadows from adjacent homes or buildings. It is easy to cut down on light that is too intense; it is relatively impossible, however, to provide light when the greenhouse is shaded by forces beyond the owner's control. In planning the construction of a greenhouse, there are a number of factors to be considered. Most demand professional advice.

Structure
The foundation of a greenhouse is an additional but necessary expense. All greenhouses should have one. In areas where temperatures dip below 35 F, the foundation, whether of poured concrete, brick or cinder, must extend well below the frost line. Otherwise, the greenhouse will warp and twist. The floor is always the leveled earth, never a slab of concrete, thus ensuring proper drainage. A clay-earth floor may be covered with several inches of cinders or gravel.

Benches
Construct the height and width of benches for convenience, generally 30 inches tall and 33 inches wide. The center bench may be twice this width as it is accessible from two sides. Select treated lumber that is resistant to moisture, or aluminum and steel, which have proven more durable, even though initially they are more expensive. The top surface of the benches should provide aeration and so should be formed either by redwood or cypress strips, spaced about their own width apart, or by a strong aluminum mesh. Air can thus circulate upward through the pots.

Heating
A heating system is essential in any area that has recorded temperatures below 45 F. It is wise to provide an emergency heater as well. Too many collections have been lost to freezing due to oversights, power failures or lack of proper maintenance of the heating system. A wide choice of heating systems is available: steam, circulating hot water, ducted hot air, natural gas. Where bottled gas must be used, absolutely no fumes should penetrate into the greenhouse. Orchids are notoriously susceptible to ethylene gas and will soon die if any is present.

Cooling and Ventilation
Except in very warm climates, a cooling system is usually not essential, because manual ventilation is adequate for those extra warm days. To grow odontoglossums and similar cool-growing genera, it may be advantageous, even necessary, to invest in an evaporative cooler in order to provide the low temperatures these orchids require. Automatic humidifying devices are necessary and should run in conjunction with adequate ventilation mechanisms. Side and roof vents operated automatically or manually, in addition to several fans running continuously, will keep the moisture-laden air moving freely throughout the greenhouse. Shading will depend largely on the characteristics of the particular climate and will have to be adjusted accordingly.