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.
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. 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.