The dendrobium tribe includes only four genera, three of which are not widely grown. The fourth, Dendrobium, more than compensates with its enormous number of species; estimates range from 900 to 1,400 or even more. Natives grow from India, China, and Japan through Indonesia to Australia, New Zealand, and the islands of the Pacific.
These orchids are highly variable in size and appearance; the largest is 10 feet or more in height, whereas the smallest require a magnifying glass to detect the flowers. The flower colors include white, cream, yellow, orange, pink, red, lavender, purple, and blue-plus almost any conceivable combination of these. Dendrobium habitats include mountainous monsoon-region forests, tropical highlands, steaming jungles, and pine forests. Practically all dendrobium orchids are epiphytes, though a few are lithophytic, living in pockets of moss and leaf mold on rocks and cliffs.
Although some species possess fat pseudobulbs, most have thin, erect or pendent stems called canes. These emerge from a rhizome but are usually tightly clumped together. Inflorescences bearing from 1 to 100 or more flowers arise from the upper portions of the cane. Plants thrive in small pots, so need infrequent re-potting.
Their basic requirements are plenty of light and free air circulation. If you grow them in the house, give them an east window or a west or south window covered with thin curtains. Keep the humidity up with misting or by positioning plants above trays of wet gravel.
Given their wide natural range and highly varied structure, it follows that not all dendrobiums will thrive under the same conditions. The species mentioned here fall into one of two classes. The first, the cool-growing species, are generally deciduous. Water and feed these during growth; then allow the orchids a decided winter rest, with either no water or just enough to keep the canes from shriveling. During their rest, they appreciate cool nights of about 40° to 50°F (4° to 10°C). The warm-growing species are generally evergreen and require water throughout the year, though they will need somewhat less in winter.
The genus has been classified into a number of different sections. Space does not permit a discussion of other than the seven sections below, but the majority of the species of horticultural importance are included in these. As could be expected the cultural requirements of this diverse group vary somewhat. If in doubt, the best approach is to treat them in all respects as if they were cattleyas but with a little higher light intensity. Dropping of leaves in the winter suggests those particular plants should be kept quite dry during this season.
A small section of Asian species with deep green leaves of good substance confined to the upper portion of swollen canes. These can be grown in the same way as cattleyas, including minimum temperatures of 50°F (10°C), but require less water in winter. A few hybrids have been made, but species are more common in collections. The examples below are all spring-flowering.
- Dendrobium densiflorum
- A 12 in (30 cm) four-angled pseudo bulb plant with a stem carrying many yellow 2 in (5 cm) flowers with fringed lips. Spectacular in flower, but the blooms are not particularly long-lasting.
- Dendrobium palpebrae
- A similar plant to the one above but the flowers are white with some orange in the lip.
- Dendrobium trigonopus
- Waxy, 2 in (5 cm) yellow flowers with a green base to the lip. The glistening flowers are spectacular and immediately attract attention.
Orchids from this section grow naturally on the coast on the wetter side of the great dividing range in eastern Australia. They are epiphytes or lithophytes with leaves of good substance on the top of pseudobulbs that are relatively slender and wider at the bottom. An enormous amount of hybridizing has been done with this section in Australia and many attractive hybrids of great horticultural merit are now being seen both in this section and incorporating other sections. The three species below are commonly cultivated and line breeding within each of these has given us some flowers of superior form and color. Grow in bark-based media.
- Dendrobium falcorostrum
- This one is definitely a cool-growing orchid, appearing naturally as an epiphyte in the great dividing range in eastern Australia at elevations above 3300 ft (1000 m) in cool, moist, cloud forest. This area often experiences light dusting of snow in winter. The near-terminal racemes bear many fragrant, pristine white flowers about 1 1/2 in (4 cm) across in spring. This orchid will grow in the same potting medium as the others in this section. The orchid is reported to do particularly well on a slab of tree fern. As a cool-grower, it dislikes high daytime temperatures. However, it still needs high light -even full sun – in winter. D. falcorostrum is one of the most beautiful species in this section.
- Dendrobium kingianum
- A common, easily-grown orchid, mainly lithophytic in nature. The size of the plant can vary from 2 in (5 cm) to as much as 20 in (50 cm) high but is commonly about 8 in (20 cm), with the inflorescence of six or so flowers arising from a bud at or near the top of the pseudobulb. The flowers are up to 1 1/2 in (4 cm) across. Flower color can be from white through pink to deep mauve. They prefer an altitude of about 1000 ft (300 m) in nature but have been found growing up to 4000 ft (1200 m).
These orchids like good light and can be grown in the same medium as for cattleyas. In hot summer months, they should not quite dry out between watering but must be kept drier over fall and winter months to encourage flowering in spring.
They may make aerial growths or keikis (a Hawaiian name for babies) that will produce roots and these can be removed and potted or left on the plant to flower. D. kingianum will tolerate temperatures down to almost freezing without coming to any harm. It is one of the few orchids that often succeeds in the hands of someone who otherwise knows nothing about the cultivation of this plant family.
- Dendrobium speciosum
- By far the largest plant in this section. Two to six leathery leaves and long racemes with up to 80 densely packed; 2 in (5 cm), or larger, white to yellow flowers. A large plant in flower is spectacular. This is a variable species that is found in Australia from northern Queensland down to Victoria, a distance of some 3000 miles (5000 km) north to south. Southern forms are quite cool-growers and should be grown much the same as D. kingianum. However, the species does like plenty of light, and it can be left outside in full sun where it will tolerate light frosts but needs shelter from wind and rain to preserve the flowers.
- Dendrobium tetragonum
- A rather variable species with a wide latitude range. The pseudobulbs are thin at the base and thicker and four-angled at the top, where the weight often results in pendulous growths. The length of these is as variable as D. kingianum. Two to four greenish or yellowish, spidery, 5 in (12 cm) flowers are borne on short stems. Flowers in spring. Some northern forms can flower at any time, but these like higher minimum temperatures. This orchid is an epiphyte. Intervals between watering should be increased in winter even to the point of a slight shriveling of the pseudobulbs.
Orchids in this section are sometimes referred to as soft cane dendrobiums, although the term is a little misleading. The plants mentioned below are all epiphytes, and they will survive winter night temperatures down to 37°F (3°C) if kept dry.
- Dendrobium nobile
- The species grows naturally from the Himalayas down as far as Vietnam at elevations up to 4000 ft (1200 m). Finger-thick canes, up to 20 in (50 cm) high, tend to drop their leaves when mature and in spring bear flowers as large as 3 in (8 cm) across, in clusters of up to three, from the upper nodes. Temperatures near freezing are not a problem in cultivation, nor is warm or even hot summer weather. Flowers are in shades of pink to purple and there is a white form (var virginalis). These orchids can be potted using the same medium as for cattleyas. Longer canes tend to be pendulous and are usually staked upright to give the best flower display.
There are quite strict rules to observe if this species is to produce flowers in spring. During summer, water frequently and ensure that they do not lack nutrients. During this time about 3000 foot-candles of light is adequate. From early fall, decrease the watering frequency and cease giving them any nitrogenous fertilizer – but continue to feed them with phosphorus and potassium. At this time the orchids require much more light, even full sunlight. From the onset of winter, cease giving any nutrients and water only to arrest any shriveling of the canes. Normal watering and nutrition can be resumed when flower buds appear. Failure to observe the rules will result in long canes that produce aerial growths or keikis instead of flowers. These can be removed and potted when they develop roots.
- Nobile hybrids
- Over 100 years of hybridization, occasionally incorporating other species, has given us tetraploid plants with thicker, shorter canes and larger, more shapely, long-lasting flowers. These modern plants have blooms of considerable beauty and are now often referred to as Yamamoto hybrids. Mr. Yamamoto, in Japan, has done more to bring them to perfection than any other of his predecessors of earlier times.
These hybrids should be grown in the same way as Dendrobium nobile species.
- Dendrobium aphyllum
- A widespread, showy, Southeast Asian species with long, pendulous canes. The mature canes drop their leaves in winter and produce 2 in (5 cm) white to mauve flowers along the length of the cane in spring. This species can be grown the same way as nobile dendrobiums but does appreciate slightly higher minimum winter temperatures (50°F/10°C). D. pierardii is a very similar, perhaps the same, species.
- Dendrobium fimbriatum
- A cool- to warm-growing species found in Southeast Asia. Many 2 in (5 cm) flowers are borne on long, leafless canes in spring. The flowers are golden yellow with a pretty fringed lip. Treat much like nobile dendrobiums, but some water is needed during the winter months.
- Dendrobium heterocarpum (aureum)
- A wide-spread and variable species. Most varieties in cultivation are cool-growing and should be given Dendrobium nobile treatment in the winter when they drop their leaves before flowering from leafless canes in early spring. The flowers are 2 in (5 cm) across and are pale yellow. This species appears in the early ancestry of yellow nobile-type hybrids.
This Asian section has deep green leaves and stout canes, which are covered with black or brown hairs. They can be grown with the same light levels and potting media as cattleyas. A humid atmosphere is desirable. Temperature requirements vary with the species. Flowers in this section come in winter and spring and have white petals and sepals and, although they appear somewhat papery, they are quite long-lasting.. Hybrids within the section have been made but the species mentioned below are all attractive plants and are quite common in collections. These are evergreen dendrobiums – they do not drop their leaves in winter and do not have to be kept dry during this season.
- Dendrobium bellatulum
- This is a dwarfish member of the section with canes about 4 in (10 cm) high. The flowers are up to 1 1/2 in (4 cm) wide with a colorful red-orange lip. Fairly cool-growing with minimum winter temperatures of 50°F (10°C). A similar but even smaller species is D. margaritaceum.
- Dendrobium formosum
- This one is related to D. infundibilum but, although it has been found growing at high elevations, plants in cultivation seem to need warmer minimum night temperatures (54°F/12°C) for best results. Canes are up to 18 in (45 cm) long and bear starry white flowers larger than those of the other two species described here.
- Dendrobium infundibilum
- Originally found at quite high elevations, this species is a cool-grower with canes typically about 16 in (40 cm) high and 3 in (8 cm) or larger flowers borne towards the apex of matured growths. Quite common in cultivation. D. jamesianum is a similar, or perhaps the same, species.
Orchids in this section are small plants native to Irian Jaya and Papua New Guinea or outlying islands with a few extending to the Pacific. Some species have been brought into cultivation only fairly recently. They are high-altitude plants that rarely survive if brought down to sea level within the tropical latitudes where they are found. They are not difficult to cultivate in temperate climates where they are still definitely cool-growers, withstanding temperatures down to near freezing but disliking intense dry summer heat. In summer, frequent misting and good air movement will help, but shade them more if necessary to keep leaf temperatures down. Some species in this section occasionally grow in full sunshine in nature but be cautious about subjecting the plants to this in cultivation.
There are about 28 species in the section. They tend to have “upside down” flowers, with the lip uppermost. Those mentioned below may all be grown under similar conditions. As to potting media, almost everything including sphagnum moss has been tried. In nature, the plants alternately become wet and dry daily so a quick-drying medium is important. The safest is probably a bark-based mix as for cattleyas, but do not let any of them remain dry at the roots for more than a day at the most. Firm rules for the successful cultivation of oxyglossums have not yet been agreed upon so do not be afraid to experiment.
- Dendrobium cuthbertsonii
- D. sophronites was the name originally given to this species by the botanist Schlecter because it reminded him of the unrelated Sophronitis coccinea from Brazil. This is the gem in the crown of the genus with flowers that last in perfection for six months or even longer.
The plants are small, about 2 in (5 cm) high, with leaves of heavy substance on top of small pseudobulbs. The flowers give the appearance of being almost larger than the plants, up to 1 in (3 cm) across and a 2 in (5 cm) pot can have a dozen flowers. The common color is scarlet or orange, but there are yellow and pink or magenta forms and bicolors with a combination of two distinct colors. Not found in other orchids are the dense prominent warts on the upper surface of the leaves, the purpose of which is not clear.
Dendrobium cuthbertsonii grows in Irian Jaya and Papua New Guinea at altitudes of up to 10,000 ft (3000 m). This orchid is an epiphyte, on moss-covered trees in quite heavy shade and even as a kind of terrestrial in the open on high-altitude grassland. This suggests the orchid may be able to adapt to a wide range of conditions in cultivation. Particularly fine plants have been grown on tree-fern slabs. Plants raised from seed tend to be easier to grow than those removed from their native habitat. The two-spotted mite likes this species and can literally destroy plants. It is impossible to spray under the leaves. Invert the pot and dip the foliage in a miticide.
- Dendrobium laevifolium
- A compact, 4 in (10 cm) high orchid with usually two leaves atop flask-shaped pseudobulbs. The flowers arise from leafless older bulbs at any time of the year but particularly in fall in cultivation. Most of the plants in cultivation are from Rossel Island, east of Papua New Guinea, and the flowers are deep rose or mauve in color -about the same size as D. cuthbertsonii or a little larger.
Plants with lighter colors, or even white flowers, have been reported from Bougainville, the Solomon Islands, Vanuatu and elsewhere. This is a pretty species, somewhat less demanding in cultivation than D. cuthbertsonii.
- Dendrobium prasinum
- This species deserves to be grown more widely. It is similar to D. laevifolium but the deep green leaves have more substance and the flowers are white. It grows naturally in the islands of Fiji.
- Dendrobium sulphureum
- A variable species. The plant is about 4 in (10 cm) high, with several leaves on the upper half of thin, cylindrical, clustered pseudobulbs bearing one or two flowers up to 1 in (2.5 cm) long. The flowers are yellow or yellow-green with a striking, contrasting, orange lip. This is a pretty species and can be grown the same way as other oxyglossums.
- Dendrobium vexillarius
- This is the most abundant of all the Irian Jaya species in this section and is found as an epiphyte in a wide range of habitats (up to over 10,000 ft or 3000 m), in color forms from blue to dark crimson. A somewhat taller plant than the others mentioned here, D. vexillarius has slender pseudobulbs, swollen at the base, with two or three leaves on top.
The flowers, up to 1 1/2 in (4 cm) wide, are borne in clusters of several flowers, more than one flower stem often coming from the same node at the top of the bulb. Some growers find this species easy to grow but others say it is difficult. The reason for this is not clear, but it is a worthwhile plant to have. Try giving this orchid the same conditions as other oxyglossums.
There are only a few species in this section but two are very important -Dendrobium phalaenopsis and D. biggibum. Both are often regarded as the same species. They are found in the north of eastern Australia and in Papua New Guinea and Indonesia. The canes are typically about 12 in (30 cm) high but can be much higher. They are cylindrical and slightly swollen in the middle, with a few leathery leaves at the top. The flower stem has many 2 in (5 cm) or larger, long-lasting flowers in white or shades of pink through to intense, deep purple. D. biggibum, the Cooktown orchid, is the state flower of the state of Queensland, Australia. The shape of the flowers is reminiscent of the quite unrelated genus Phalaenopsis, the moth orchid.
These plants come from areas with hot, wet summers and somewhat drier winters and this indicates their requirements in cultivation. They must be dried quickly between watering in all seasons, and need a quick – draining potting medium. Keep them in as small a pot as possible. The plants can stand quite high light intensities. Grown indoors, they will survive with minimum night temperatures of 50°F (10°C), but for best growth and flower quality in the fall, they really need minimums of nearer 60°F (15°C) all year. These are tropical orchids.
The plants in cultivation labelled Dendrobium phalaenopsis will probably have been the product of line breeding over several generations with flowers of impressive size, conformation and color. Much hybridizing with other sections has been done, particularly with section Spatulata. All these orchids are easy to cultivate in the tropics and are shipped around the world from Southeast Asia in a multimillion-dollar cut-flower industry. If living in a warm temperate climate, try growing D. biggibum ‘compactum’, a smaller, free-flowering plant from Queensland. Many succeed with it outdoors in subtropical climates such as Florida.
These used to be known as ceratobiums. A feature is the twisted sepals, which often go straight up, giving the section the popular name of “antelope orchids”. The flowers are usually long-lasting. Most of the species come from low elevations or sea level and are definitely warm growers, needing a minimum night temperature of 60°C (15°C). Plenty of light and a warm humid atmosphere are beneficial. A medium as for cattleyas is suitable, but keep them growing throughout the year in small pots with frequent wet and dry cycles. Tall canes are typical, with leaves confined to the upper half. Flower stems carrying several flowers arise from the nodes of upper leaves. A few representative species are listed below.
- Dendrobium canaliculatum
- Found in Australia and Papua New Guinea growing on melaleuca trees. Flower stems carry 50 or more 1 in (2.5 cm) fragrant flowers in winter and spring. The flowers have white and yellow petals and sepals with a purple lip. Keep drier in winter than others in this section. It is a smaller plant than other spatulatas and has been much used in hybridization.
- Dendrobium gouldii
- A common species found growing over a wide geographic area. Flowers are 2 1/4 in (6 cm) across in white or pale violet with rarer golden yellow forms. Also widely used in hybridization.
- Dendrobium stratiotes
- This is a majestic species with 39 in (1 m) high canes and large, long-lasting flowers with white petals, yellow sepals and a violet lip. Flowers throughout the year.
- Dendrobium tangerinum
- The 3 in (7.5 cm) flowers have bright orange petals and yellow sepals and lip. This colorful plant was grown for many years under the name ‘Tangerine’. This orchid has been the parent of many hybrids.