Delightful Dendrobiums

By David Johnston

David started his collection with some Phalaenopsis, subsequently adding to it with dendrobiums and vandas, all of which he grows to perfection, as well as several other genera in a converted conservatory and a couple of greenhouses.

The key to being successful with dendrobes is the winter treatment, which can make or break the flowering season. Obtaining books on the genus is essential as there are no guidelines that cover all species (notable books by Lavarack and Baker & Baker). Dendrobiums are found throughout the Asiatic tropics from India in the west to Japan in the north, down to Australia and New Zealand. In between lay mountainous islands such as Borneo and New Guinea where conditions can be cooler at altitude. The botanists have split up the 1000-1300 dendrobiinea species into various genera with about 800 true dendrobiums within around 36 sections, but David thinks that for the grower, they can be split mainly into cool, intermediate and warm groups – with some variants.

Dendrobiums can be tiny to very big plants with tiny to large flowers. Their main identifying feature is their floral spur or mentum. They grow mainly in trees, but can be found on rocks or in moss. Some are deciduous. Cool types come from the mountainous regions with high humidity, often windy, and frequently in full sun, although summer maximum temperatures rarely exceed 25C. The seasons around the equator don’t vary much, but do have wet and dry periods. Intermediate types are found to the northern and southern ranges, and on lower slopes where they experience a minimum of 12-13C at night rising to 32C maximum in summer. They will have some shade and seasonal variation at the northern & southern extremes with dryer humid winters and wetter summers. Those from the Philippines and Papua New Guinea tend to grow all year with little variation in temperature. The warm types are found nearer to sea level where they are have good shade in often very hot temperatures of 35C, but cooling to 20C at night. They can get very wet, and have high humidity all year, with often little seasonal variation. A lot of these types are suffering from deforestation as humans colonise all the lower land and less steep slopes for food production.

As there are such a large number of species, it is only possible to show a few of them in the time available, and these are the relatively commoner ones.

Selected Cool growing species

moniliforme is found at high altitudes on the Japanese islands. It is white, with a tinge of pink.

victoria-reginae is also a high altitude plant, from the Philippines. It has clusters of purple flowers appearing usually from the old leafless canes.

cuthbertsonii is a true miniature within the dendrobiums. It comes from New Guinea, and varies in colour from white to purple, and even yellow. It can be difficult to grow, and needs high humidity, with good air movement.

Selected Intermediate growing species

forbesii is from the Philippines, with an almost constant year round temperature. It has twisted white petals.

lowii is from Sarawak, and has yellow flowers with red ridges on the lip.

cyanocentrum is from Papua New Guinea, and has unusual shaped blue to yellow flowers, as well as an alba form.

sanderae is a tall species from the Philippines having canes over 2’ tall and 3” white flowers with red ridges on the lip.

pseudoglomeratum is from Papua New Guinea, and has a conical mass of tiny almost luminous pink flowers on the old canes.

obtusisepalum (chrysopterum) is from Papua New Guinea, and has large glossy orange/yellow flowers.

aberrans is from Papua New Guinea, and is characterised by its short bulbs, and has small white flowers.

lawesii is from Papua New Guinea, and has arching or drooping canes, so is best in a basket or cork. The flowers are small, and usually clustered. It is normally red or orange, but can have white tips, or be pure white.

transparens is from India/Burma, so is a bit more seasonal the PNG species, and requires a winter rest. Often the pot will appear to hold just a bunch of twigs, but then in spring many pink edged white flowers will appear.

aphyllum from Burma has very floppy canes, best grown in a basket and has pink/white flowers.

gracilicaule is from Australia, and needs a cool winter rest. This close relative of kingianum has pale blotchy flowers.

loddigesii is from SW China, and has pink flowers with a yellow centre on flexible twisting canes.

unicum is from Thailand/Vietnam, and has 2-3 bright orange flowers along the old canes. It has a shoe like lip.

secundum is a widespread species, generally with a cluster of upwards facing pink flowers, but also has a white form. Can be kept cold in winter and even hot in summer.

tetragonum is from SE Australia and has very spiky yellow green flowers

infundibulum is from Burma, and has large almost transparent white flower with orange centres.

amethystoglossum from the Philippines has small white flowers with purple blotches, and benefits from a warm humid dry winter rest.

Selected Warm growing species

bracteosum is from PNG and has bunches of small pink flowers that can hide all the canes.

cruentum is from Thailand. It has pale flowers with a red edge to the lip.

glomeratum is from PNG where it grows near to swamps. It has pink/purple flowers that can reach 2 1/2” across.

mohlianum is from Fiji & the Soloman Islands. It has clusters of small orange flowers.

mutabile is from Java and Sumatra and produces almost round white flowers on slender canes.

goldschmitianum is from the Philippines, and produces bunches of tiny pink flowers.

sulcatum is from Burma where it can be quite cool in winter. It produces clusters of smallish yellow flowers.

Selected hybrids

Stardust is a popular unicum (x Ukon) hybrid that has 2 notable clones – ‘Chiomi’ that is pale yellow, and ‘Firebird’ that is as orange as its parent. Grows intermediate.

Kunico is a primary hybrid of victoria-reginae x goldschmitianum and produces small violet striped flowers. Intermediate.

Thwaitesiae is an old hybrid (1903) of Ainsworthii x Wiganiae, and has yellow flowers with a dark centre.

Cassiope is another popular primary hybrid, and even older at 1890. The parents are moniliforme x nobile. It is a fairly short plant with small white flowers with a purple centre. Intermediate.

Golden Aya is a relatively recent hybrid to produce near flat yellow flowers (se back cover). The parents are aphrodite x capillipes. Grows intermediate.

Fire Coral is a cruentum hybrid. It is a tall plant of white flowers with a red centre.

Green Lantern is another cruentum hybrid and has white flowers with an orange lip, grows warm/intermediate.

Precious Dawn has cruentum as grandparents, so still keeps the similar shape, with a whitish flower, but with a yellow lip increasing to brown at the back.

Pua’ala is a Hawaiian hybrid with spectabile as a parent, yet is a clear purple colour – which comes from the bigibbum grandparent (the other is macrophyllum).

Andree Millar is a popular primary hybrid (atroviolaceum x convolutum) with twisty yellow flowers with a hairy purple lip.

Aussie Treat is a kingianum type hybrid from Australia and has small whitish flowers, best grown cool.

A few questions followed, mainly on when is best to remove old canes as many quickly become shrivelled and distorted. As long as these are greenish, then they can in many cases still produce flowers. Once they become yellow then they are no longer productive and can be removed. Many thanks David. JG