Orchids are further classified as to type of growth. The familiar cattleya grows from a horizontal rhizome that sends out roots from below and a "lead" each year from above. The lead curves gradually upward to an erect leathery growth from which a flower bud emerges. The lower part of the lead enlarges to form a pseudobulb and a leaf emerges at this point. Such orchids are known as sympodial or "feet together" and this is the more common type.
The monopodial or one-footed orchids include the vandas and angraecums. With these, a stem extends upward and leaves develop alternately along it. The flower spikes emerge from the leaf axils. Then there are orchids, such as the dendrobiums, that are further classified as evergreen or deciduous. For example, Dendrobium nobile drops leaves from its reedy pseudobulbs about the middle of the second year and flowers then appear along the almost leafless stems. The evergreen cane-type Dendrobium thyrsiflorum retains its broad fleshy leaves and produces handsome white clusters of orange-tipped flowers from the tops of the canes.
For greenhouse growing, orchids should be selected and grouped according to their more-or-less definite requirements of heat and light. As I have said, most of the more demanding high-temperature, high-humidity species can be accommodated somewhere in the cool or moderate greenhouse. Few require full sun; most do well in filtered sunshine or bright light. In winter, I place my orchids in the lightest possible locations in the greenhouse; in summer, light is filtered through slats or vinyl shading. (If you have an outdoor garden, you can suspend the plants from tree branches during summer.) During summer in the greenhouse, high humidity is essential and this is provided by frequent wetting down of walks and under-bench areas; of course, a mist system is ideal in hot weather, and also in winter for the high-humidity group. A good circulation of air is essential in every season.
The orchid fancier will find that benches, built in stepped-up tiers with an area of coke or gravel below, are ideal for growing and display. From the frequently water-sprinkled coke or gravel, moisture evaporates to surround the plants with welcome humidity, and the open placement in tiers assures a fine circulation of air.
In the small greenhouse, orchids are usually set on benches filled with sand or gravel but raised a little on a wire-mesh covering or on slatted sections made of half-inch redwood strips. Humidity and air circulation around roots are thus provided. If you are growing just a few orchid plants, I can also recommend the simple arrangement of placing the plants on inverted flower pots.
Culture for the various types of orchids differs somewhat but it is surprising how accommodating most of them can be. In fact, once they are established, it is not at all difficult to bring plants to maturity with minimum effort. Most specialists include directions with their plants, and new potting materials have further simplified culture.