Date: Thu, 09 Jan 1997 16:20:19 +0000 (UT)
From: "Richard.R. Trussell" <Whitmoor@msn.com>
Subject: [11941] Dendrobiums

        Our interest in Dendrobiums has led us to understand the
difficulties many newcomers have in learning how to tackle their
culture. Reading the Willis Dair lists suggests to us that these
difficulties extend to both sides of the Atlantic. Although
Dendrobiums occur naturally only in a well defined geographical area -
from India to Australia - there is within this area a very big range
of climatic and environmental variation. Understanding this geography
is an important part of understanding the necessary conditions for
successful growing. A good atlas, or better still a good globe can be
as valuable as a textbook!  We have put together the folowing notes
for the British Orchid Growers Association "Growers and Buyers Guide,
1996-97" and offer them as possible assistance to those tackling their
first plants of this fascinating and important genus.
        Dendrobiums come from South East Asia in an area that
stretches from Northern India to the islands off the East coast of New
Guinea and Australia , and to Polynesia. The latitude where they grow
is important. The Equator runs through the middle of the territory,
and here it is always hot at sea level witout any seasonal
variation. However the plants frrom north of the Tropic of Cancer and
south of the Tropic of Capricorn are used to a much greater range of
climate, with colder drier winters and warmer wet summers. It is
important therefore to know where every plant comes from.
        For convenience we consider cultural advice under three headings,
1. Nobile (pronounced no-bill-ay) type, or Himalayan plants.
2. New Guinea plants
3. Australian plants.
Nobile Dendrobiums
These are some of the easiest to grow, but can be a little difficult to bloom
regularly. Their flowers are showy with colours ranging from white through
pink to purple, and the lip is often beautifully marked  in contrasting
colours. They make magnificent specimen plants Others are yellow or brown,
while the recently introduced Yamamoto hybrids have all the colours of the
rainbow. The Himalayan climate is not unlike a warmer Switzerland, with
bright, cold but dry winters.
        Culture. November to February: day time temperatures can drop
to 40-45F, during this time you should not water or feed, but provide
plenty of light and air movement. March to May or June, warmer and
moister conditions; buds and flowers develop and new growths
appear. Water sparingly until the new growths have developed good
roots. June to November corresponds to the Monsoon period, warm and
very wet. Give a low strength, high nitrogen feed in April and May,
then feed weekly with a balanced fertilizer during maximum
growth. Change to high potash for the last month, October. Note - if
you do not dry and cool the plants during winter you won't get
flowers! Himalayan Dendrobiums from lower altitudes need a less harsh
winter, but still dry.

New Guinea Dendrobiums
The climate varies with altitude and in the mountainous areas there are cool,
wet misty  nights and mornings followed by warmer bright days. The exquisite
cool and intermediate miniatures like D.cuthbertsonii grow here. Never allow
them to dry out completely, and feed often with dilute fertilizer. The river
valleys between the mountain ranges are warmer and wetter, and home to some of
the most exotic of New Guinea orchids, e.g. D.lasianthera from the Sepik River
basin, and many latouria types with long lasting flowers. All these need
generous feeding and watering. The southern plains resemble Queensland,
Australia, but are wetter and very warm all year through. There is seasonal
rainfall variation with a wetter summer and drier winter. Two of the
outstanding species from this area, (which are also found in Queensland ) are
D.bigibbum (D.phalaenopsis) and D.canaliculatum, the former often found
growing on rocks, the latter on the trunks of paperbark trees. The easiest New
Guinea plants for beginners are D.aberrans (cool conditions); D.lawesii or
D.antennatum (intermediate), and D.atroviolaceum or D.bigibbum (warm).

Australian Dendrobiums
D. kingianum and near relatives are the easiest to grow. The pseudobulbs or
canes can be any length from 5-30cm tall, and are thin and often spindly and
tough. The leaves are narrowly oval, with two to four at the top of each cane.
The flowers appear in late winter or early spring in loose sprays at the tops
of both old and new canes. New plantlets or keikis may sometimes appear
instead. These can be removed and potted separately after they have developed
good roots or left onb the parent plant where they will eventually flower
also. There are two to ten flowers on a spray, each measuring 1-3cm across in
shades of pink or purple. Other plants in this group  may be taller andd have
cream or white flowers. For their culture give intermediate temperatures and
drier conditions than other Dendrobiums. Spray once a week, and water
generously in the spring and autumn with dilute feed. A few cold weeks, down
to 45F, will encourage flowering.

Potting
Dendrobiums like to be in small pots with their roots confined. Bark, perlag
and charcoal make up an open mix which drains easily. Repot either when the
compost becomes acid and soggy, or when the pot is full of roots. This often
means every year. Plaants frrom the mountainss of New Guinea like a little
mosss mixed with the bark, or they can be grown on slabs of bark or treefern
on a mossy bed. Such slabs need daily misting for most of the year.

Dendrobium hybrids.
These are almost always derived from species within one group, either
Himalayan, New Guinea or Australian. Surprisingly, most of the 'Singapore'
orchids, although developed there, are derived from species of New Guinea and
the adjacent islands, aand need much the same culture as the River Valley New
Guinea species. So - when you buy a Dendrobium, ask which group it belongs to,
and where it comes from - and we don't mean which nursery!

>From Richard and Ann Trussell, Devon EX15 3NP, U.K.
whitmoor@msn.com