Culture of Callista-type Dendrobiums

THE Callista-type dendrobiums are orchids whose popularity and availability have probably declined as a result of the difficulty of importing wild-collected plants. There was a day, well into the 1970s, where no spring orchid show would be without magnificent flowering plants of Dendrobium chrysotoxum, Dendrobium densiflorum, Dendrobium farmeri, Dendrobium lindleyi (formerly Dendrobium aggregatum), Dendrobium jenkinsii or occasionally the winter-flow­ering Dendrobium thyrsiflorum. The sales marts would always have plants of these species available, either bare-root, or re­cently established.

Opposite above left: Dendrobium lindleyi (syn. aggregatum) `Kiyooko', CCM/AOS, grown by Kiyooko Sproat. Opposite above right: Dendrobium farmeri `Jo Ann Lapointe', AM/AOS, grown by Jo Ann Lapointe. Opposite below: Dendrobium densiflorum 'Meredith Ann', CCM/AOS, grown by Spencers' Greenhouse.
Above left: Dendrobium lindleyi (syn. aggregatum) `Kiyooko’, CCM/AOS, grown by Kiyooko Sproat.
Above right: Dendrobium farmeri `Jo Ann Lapointe’, AM/AOS, grown by Jo Ann Lapointe.
Above below: Dendrobium densiflorum ‘Meredith Ann’, CCM/AOS, grown by Spencers’ Greenhouse.

Unfortunately, Indian nurseries, which are the major suppliers of these species, have not found these to be of sufficient appeal to have raised popula­tions from seed, nor have domestic nurs­eries seen fit to propagate these on any significant scale. Now we see them all too rarely.

It is unfortunate, too, that as a result few newer orchid growers have been ex­posed to just how lovely well-flowered examples of these species can be. And lovely they are, with their cascading in­florescences of cream or golden flowers emerging from the upper nodes of the upright canes. The exception to the rule is Den. farmeri, which is lilac with a con­trasting yellow lip.

This group is also known for produc­ing large specimen plants fairly easily, which are all the more spectacular when in their spring-blooming season. If this group of dendrobiums has a drawback, it is that the flowers are not particularly long-lasting, giving an unmatched dis­play for only two weeks before fading.

How to Grow the Plants

There are those growers who claim that these plants flower for them with no special treatment. This assertion is backed by wonderful spiking and a beau­tiful display. There are other growers who have learned, in most cases the hard way, that this group will not perform for them no matter what special treatment they give the plants. Most of us will find our­selves somewhere in between. We find the extra notice needed by these beauties to be worth the effort.

In any genus the size of Dendrobium, with more than 1,000 species, there is bound to be a variety of cultural regimes to which the plants will respond. This group, known as Section Callista, gener­ally comes from the middle elevations of the Himalayas, where monsoonal condi­tions — seasonally hot and wet alternat­ing with cool and dry — prevail.

Watering: During the season of ac­tive growth, the plants require copious amounts of water and fertilizer, as well as bright light. After the plants have made up their pseudobulbs for the year, they require an almost complete withdrawal of water, and a cessation of nitrogen-based fertilizer. This is similar to what would be happening to them in their na­tive locales. Most writers will temper this advice by a statement like “water only enough to prevent shriveling.” Good, though imprecise. The occasional water­ing, or rainfall, will not interrupt the rest period of this type enough to prevent their blooming. However, be careful not to give the plants any appreciable nitrogen.

Fertilizing: As noted above, feed heavily with a balanced fertilizer during active growth, usually March through August, tapering off the nitrogen in late summer to allow the pseudobulbs to “finish” and mature. Excess nitrogen will result in fewer or no flowers.

Light :This type of dendrobium is best grown under light conditions pre­scribed for cattleyas — bright light with some protection from hottest noon-day sun. In more-tropical areas with humid­ity, these will take almost full sun, as with vandas. Owing to their high light require­ments and somewhat tall — 15 to 18 inches or more — stature, these are not the best for under lights. If they can be summered outdoors, they may succeed if they can be grown within a few inches of the lights.

Temperature: In their native habitat, temperatures are uniformly warm during the growing season, often in the high 80s, with not much of a drop in the evenings, unless the monsoonal rains are protracted, in which case the temperatures may drop into the 60s. Cool nights, into the 50s, are the rule in the dry season, with days up into the 70s as a result of the high light conditions that prevail in the often de­ciduous forests of the region.

Potting: The best plants of this group seem to be grown in a porous mix in slatted baskets. These conditions allow the frequent watering necessary, while also permitting the quick drainage demanded by this group. The grower needs to mimic the high summer rainfall to which the plants are accustomed in their natural habitat. As autumn approaches, and the growths begin to mature, a gradual reduction in water and fertilizer is indi­cated. The maturity of the growth is shown by the appearance of the terminal leaf on the pseudobulb. Callista-type dendrobiums are often sold mounted on wood or tree fern, though basket culture seems to be the mode of choice for grow­ers of larger and more-floriferous plants.

Insect and Disease Problems: There seem to be no particular insect or disease problems unique to this group. As with all orchids, maintaining a clean growing area and inspecting plants once a week will curtail problems.

By Ed Nash. Reprinted with the permission of the American Orchid Society, May 1997 Orchids.