This genus of orchids once made fortunes for plant collectors, for the plants died almost as fast as they could be imported, and consequently became rare. Even after the rules of orchid culture were clearly established, dendrobiums were tagged as temperamental. This was natural because so little was known about them for so long. The approximately 600 known species are spread over a vast area in the Eastern Hemisphere from the Indian Himalayas to the Philippines and down to Australia. Several members of the family spill northward into Japan and others southward below the equatorial belt into New Zealand. It took naturalists many long and weary years to explore this region and to determine the two simple facts that made dendrobiums respond to culture: There are two types of dendrobiums and two distinct climatic conditions under which they grow. By virtue of this knowledge, dendrobiums today are as easy to grow as saying your ABC's.

Dendrobiums (the word means "tree-life") resemble bamboo. This is one of their visually unmistakable characteristics. The pseudobulbs are noded, slightly narrowing at the leaf axils in much the same manner as in bamboo. Usually the pseudobulbs are much longer in proportion to their thickness. They may vary from one-fourth inch to several inches in diameter and from one inch to three or more feet in length. Flowers are freely produced from apical spikes or in clusters of two and three flowers from the nodes along the pseudobulbs. Instead of flowering only once a year, the Indian and Burmese dendrobiums have the pleasant habit of producing two or three spikes at irregular intervals. Although the flowers are rarely larger than four inches, the floriferousness of the plants and the gay colors make them more decorative than most orchids. In no other genus of orchids are there more perfect golden yellows, fiery oranges, brilliant reds, and pure whites. Dendrobiums tend to revoke the practice of growing only the best hybrids. Many species have not been excelled by their hybrid progeny. Many of the flowers have spurs or little nubs at their bases which give them something of the appearance of oversized nasturtiums or gaudy aquilegias. This is another visual characteristic by which you can identify the family.

Culturally the dendrobiums are divided into two classes: the evergreen plants from Australia and New Guinea—typified by Dendrobium phalaenopsis—aná the deciduous plants from the mountains of India and Burma—of which Dendrobium nobile is one of the most popular. A third but relatively unimportant group is listed by some authorities; as the first two groups merge in the Malay Archipelago they produce abortive plants which may be evergreen and yet require the same culture as the deciduous members. Dendrobium formosum (one of the finest white orchids) is about the only one of this group you are likely to grow. It grows luxuriantly along the sea coasts of Malaya and the Andaman Islands, where it is often drenched by salt spray.

Plants in the evergreen section, while requiring more constant attention than those in the deciduous group, are not hard to grow if they are confined to glass structures where you can control atmospheric conditions. They require high humidities; syringing or table trays may not provide sufficient atmospheric moisture. They can be used as table and window decoration when in bloom because the drier air of the room will prolong the life of the flowers. However, as soon as the flower season is finished put them back into Wardian cases or greenhouses.

Evergreen dendrobiums are never really at rest and never lack for water in their native countries; they must be similarly obliged in culture. And, oddly enough, though they have uniformly larger pseudobulbs than their leafless cousins, they are more tender and require the higher temperatures of the intermediate or warm class of orchids. You can combine them quite successfully with cattleyas in the same structures; this is one of the nicer workable combinations in the orchid genera.

If you select dendrobiums to grow at home in cases or greenhouses, try the deciduous ones first. They are as nearly foolproof as orchids can be. Most species belong to this group, thus making it easier for you to choose plants in keeping with your pocketbook. In addition, they are buffeted about by abrupt and variable seasonal climatic changes in the Burmese mountains; as a result, they don't mind more or less casual treatment in culture. Indeed, they weren't grown successfully until early orchidists stopped pampering them. However, both deciduous and evergreen sections are hard to grow in the East unless kept in greenhouses. The reason for this is not clear since they succeed so well in the South and West under casual window culture. It is most likely that they receive too little syringing, too little light in steam-heated eastern homes.
Deciduous dendrobiums come from the northern equatorial belt, and their growing season corresponds to that of most of our garden plants, which makes them less difficult to handle. They send up new growth in spring and complete it by late fall. During this period of active growth they should be carried at an intermediate temperature with a correspondingly high humidity. Their requirements for humidity, however, are not too difficult and water trays plus frequent syringing in bright weather will keep them in reasonably good condition. Water is applied regularly to the pots though not in heavy quantities. The compost should be allowed to dry out between waterings, yet not be permitted to stay dry for longer than a few hours.

In winter the deciduous dendrobiums drop their leaves and go through the stage which orchidists variously call rest, dormancy, or a ripening period. The slight summer shade under which the dendrobiums were grown is done away with as much as possible. They are given all the sunlight they can stand without injury. The temperature of the growing case, window, or greenhouse is allowed to drop to the cool classiñcation, although most deciduous dendrobiums can stand a consistently low temperature of 40°. Dendrobium superbum has overwintered Southern California frosts. Commercial men sometimes lower the temperature of their houses in order to retard spring flowering, making it coincide with profitable Easter sales.

While at rest deciduous dendrobiums are given copious amounts of fresh air and considerably less humidity. Very little water is added to the compost—just enough to keep it moist so that roots may stay alive and somewhat active and the pseudobulbs remain plump. According to many reports, Burmese dendrobiums are sun-scorched so badly that the pseudobulbs shrivel and the roots fall off. That may be a suitable natural condition, but in artificial culture there is no sense in subjecting dendrobiums to such harsh treatment. They will work better for you under clinically ideal conditions. If you wish, try summering deciduous dendrobiums beneath the shade of yard trees. This is a most successful method of inducing good, hard pseudobulbs and insuring flowering the following spring.

Most growers stand solidly behind the opinion that the secret of flowering deciduous dendrobiums lies solely in the treatment they are given after the summer's growth is completed. Flowers are produced only from pseudobulbs that have been correctly ripened. If you overwinter plants at high temperatures the incipient flower buds at the nodes undergo a drastic change. In the spring, instead of flowers, you'll get small adventitious plants. This is a nice way to increase your stock of plants.

Dendrobiums in variety, however, can be propagated in the more customary manner without losing flowers. They tend to flower at the same time that they develop new growth, so as soon as the flowers disappear simply cut the rhizomes at the base of the plants, separating them into two or more divisions. Each piece should contain not less than two pseudobulbs.

The evergreen section normally produces along the stems young adventitious plants which may be cut off and potted. This doesn't interfere with flowering. Don't ruin the older pseudobulbs, though; they produce flowers year after year. The pseudobulbs of the deciduous section, on the other hand, bloom only once. They can be cut out of the plant and propagated by cuttings. This is a much faster method of increasing your stock than division. The long pseudobulbs are cut into three-inch to five-inch lengths, each cutting containing one or two nodes.

The cuttings are placed on moist sand in a warm, shady, and very humid spot. It is sometimes expedient to cover them with a bell glass or similar equipment in order to keep the humidity relatively high. Within a few weeks young plants will break from the nodes, and as quickly as they develop several good roots they can be potted. The young plants will have to be hardened before you replace them with your older plants. Gradually give them more air, light, and lower temperatures. Propagations should develop flowering growths in from two to three years—not really a long time to wait.

Sometimes it is a bit difficult to get cuttings to grow plants from the nodes. The time of the year seems to have much to do with it; ordinarily cuttings are made in the spring in order that young plants may have the full benefit of the growing season. However, experiments published by Lloyd C. Cosper in the Bulletin of the Plant Culture League indicate that cuttings may be forced and more and healthier plants obtained by using a growth hormone. Dip the apical ends of the cuttings into a recommended brand of a root-stimulating hormone powder. Remember, it is the apical end—the top of the cutting, not the bottom. The hormone moves downward through the plant tissues to stimulate adventitious growths. Ordinarily, dipping the bottom of a plant cutting into a hormone powder stimulates roots. But with orchids you get new growth first, then roots. As yet hormone propagating techniques have not worked well with the evergreen section of dendro-biums. They respond better to division.

Regardless of the section to which dendrobiums belong, they are potted alike. In the spring, after flowering, they may be knocked out of old pots, cleaned, and replaced in fresh osmunda. The size of the pot and the amount of os-munda are sometimes critical. All dendrobiums have thin, wiry root systems which are among the shallowest and least extensive of all orchids. They do not need large pots—in fact, the smaller the better. Leave about a half inch between the pseudobulbs and the inner edge of the pots. The leads are produced closely against the old pseudo-bulbs and don't take up much room. The osmunda rarely fills more than one-half of the depth of the pots—not the customary two-thirds. When repotting always keep the center of the osmunda slightly above the rim of the pots, sloping it downward and outward. This insures adequate and quick drainage away from the rhizomes, which are rather sensitive to having water around them.

All in all, if you wanted to specialize in one genus of orchids, it would be hard to go wrong in selecting dendrobiums. The commercial species are uniformly short in height, fitting into most small cases or windows with ease. Their requirements are not difficult. Their floriferousness is one of the wonders of the plant world—many colors and many flowers on a single plant. Normally, one adult plant will produce about twenty flowers season after season. Some specimen plants have had more than 500 flowers.

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