Friday, 16 November 2012

How to grow Dendrobium orchids

Orchids in the Dendrobium familiy (pronounced den-dro-bee-urn) come from South East Asia, covering a huge area that stretches from as far as Northern India to the small islands off the East coast of New Guinea as well as Australia to Polynesia. It is important to take a note of the latitude where they grow as the Equator runs through the middle of the growing territory and it should be remembered that it is always hot at sea level with hardly any seasonal variation.
However if one selects plants from north of the Tropic of Cancer and south of the Tropic of Capricorn these are more adaptable to growing in the UK as they encounter to a much wider range of climate variability, with colder drier winters and warm wet summers. It is important therefore to know identify where each species actually comes from.

There are well over 1,200 identified species of Dendrobium , and yet more are being classified from the highlands of New Guinea, an exciting area to plant hunters and an area that does see some cold, expect to see more tropical plants coming from this region for British gardeners. This makes them the second largest orchid genus in the world after Bulbophyllum. The family was established by Olof Swartz in 1799 and in 1981, Briegar reclassified all terete-leaved Dendrobiums from Australia and New Guinea into a new genus, Dockrillia. The Winika orchid from New Zealand was formerly D. cunninghamii, but has now been moved into a monotypic genus Winika. In 1989, Clements upgraded the D. speciosum complex into individual species similarly, the D. bigibbum complex (which contains the well-known Cooktown Orchid of Australia, D. phalaenopsis) has recently been split up.

Whilst the form as well as the shape of the individual stems and leaves vary tremendously beteen species, the pattern of flowers is reasonably constant albeit witha wide range of sizes ranging in size from very small to huge. Generally the bases of the sepals are fused to the base of the column and the lip base forming a mentum or 'chin' which typically houses the nectar of the flowers.

Light requirements
Dendrobiums like good level of light at all times but they should not be kept away from full sun or they can scorch. Keep them in the brightest position during the winter months in indirect sunlight to help ripen the current years stems/canes.

Watering requirements
This is one of the key elements that new growers of Dendrobiums often fail to adhere to, avoid all watering from mid November until February. If the atmosphere in your home is very dry or you keep them in a dry greenhouse then you can mist your plants once a months to avoid over drying them or give them a good single soak every 8 weeks. The Nobile type Dendrobiums must have a rest from water between these dates if you want to see flowers.

There is a fine balance between drying them out completely (killing them) and keeping them alive. This is due to their natural habitat in South East Asia where the winters are cool and the air fairly dry. This winter treatment is stopped in February as growth re starts and water should be applied sparingly until good roots are visibly growing from the new shoots, by June watering can given twice weekly and continued until November. This watering regime is due to the plants native environment where they would be subject to monsoon type downpours during the early to late summer with corresponding higher temperatures and humidity and cool dry winter conditions.

Dendrobium Spring Dream 'Apollon'

Potting.
Dendrobiums do better when kept in small pots with their roots confined. Bark, perlag and charcoal make up an open mix which will drain easily. Repot when either the compost becomes acid and soggy or when the pot is too full of roots. This often means every year or so. Plants from the mountains of New Guinea like a little moss 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. Repotting and dividing should be undertaken in the spring either immediately after flowering or just as new growth starts.

How to repot
Gently pull the orchid from the pot and shake loose the remaining potting mix. If orchid is difficult to remove, then consider soaking the plant, in water. If that doesn’t work, cut off the pot. A few pot pieces stuck to roots won’t impede growth in the new pot. Better to leave these on that cut roots to remove them.

Trim any dead or rotting roots with sterilized blade. Never use blade on another plant without re-sterilizing.

Add potting mix to within a cm or so of pot rim. Work roots into mix, but do not bury the base of the pseudobulb. Use a rhizome clip if you need it to secure the plant. Stabilize plant with a vertical stake and ties.

Water sparingly until new roots start.


Propagating
The Dendrobium reproduces by growing keikis or “babies” from the nodes on the stem. After flowers have bloomed, cut stem at the base and lay it on moistened river sand, Dendrobium potting mix or fir bark. Allow keikis to grow until the end of the growing season (August). These keikis should grow roots. Remove at this point and pot them in small pots.
 

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