If it were possible to have one favorite kind of greenhouse plant, mine would surely be orchids. What other plants are so easy to grow and so spectacular in results? It has always puzzled me that orchids are often thought to be difficult to grow. Cattelya orchids were among the first plants I grew and they continue to give me pleasure year after year. Many greenhouse gardeners have made the same discovery, and today orchids are everybody's flowers, appreciated by hobby gardeners the world over.
Orchid habitats extend from the arctic to the tropics, so it is possible to grow one kind or another whether you have a cool, a moderate, or a warm greenhouse. My night temperature range is 48 to 54 F; the cool and intermediate orchids do just fine, and occasionally even a heat-loving dendrobium has surprised me with bloom. The point is that in a cool greenhouse you can find areas of considerable warmth, just as in a cold outdoor garden there are warmer microclimates where heat-loving plants thrive north of their natural zone. Except for a small group, the requirement of high humidity for orchids is more myth than truth. Relative humidity ranges from 40 to 70 per cent in my greenhouse, the high point being reached only immediately after I have watered plants.
Under my conditions, many orchids thrive cattleyas, green-leaved cymbidiums, deciduous dendrobiums, reed-stemmed epidendrums, and various others. The heat-loving mottled-leaf cypripediums, the evergreen dendrobiums, and the vandas would be doubtful, though perhaps with extra daily mistings and a location above the heater, they too might perform well.
Orchids offer a vast variety of flower types and plant forms. If you are familiar only with the florist's purple cattleya flower used in corsages, you will be surprised to see the small yellow blooms of Epidendrum Stamfordianum, fifty or more to a scape, and they are fragrant, too. The pendent scapes of Dendrobium aggregatum are a veritable fountain of yellow, sometimes with more than a hundred 1-inch blossoms on a mature plant. Cypripediums (the native lady-slipper orchids are various hardy species of Cypripedium, so you may already be acquainted with this orchid genus) bear large solitary flowers, often 6 inches across, in a wide range of color; and what plant can surpass Coelogyne cristata with a dozen or more large, cascading, snow-white blooms, the throats stained a vibrant orange-yellow?
Orchid flowers remain fresh on the plants for weeks a handsome sight, indeed; but out-of-bloom orchid plants are not much to look at and you may not want them prominently displayed. In the small greenhouse, it is a good idea to grow one each of half a dozen or so different kinds that will give you fall, winter, and spring bloom; or else settle on more plants of just a couple of kinds for an emphatic effect in one season. At the end of this section is a list of a dozen easy-to-grow orchids to give you flowers through the year, even in summer if your greenhouse is a year-round affair.
Orchids are certainly fun to grow. From the time you buy your first plant to the day its first blossom opens fully, you are fascinated by the various stages of development. By all means start with mature plants purchased in bud so that almost immediately you can enjoy the color, form, and texture of unfolding flowers. Later, if orchids become your obsession as well you could grow some from seed. In that case, be prepared to wait five to seven years for bloom!