King orchid growing on a rock
(This article is for those who live in climates where they can grow Dendrobium orchids out of doors. It’s not for collectors and competition growers whose plants, especially if grown in cooler climates indoors, need a much higher degree of care).
Dendrobium orchids are very independent plants and they don’t like a lot of fuss. Gardeners who have problems growing them remind me of parents who treat their children like hothouse plants – won’t let them do this, won’t let them do that in case they come to harm. Rearing children in this unnatural way turns them into adults who lack strength of character and the ability to fend for themselves. It’s just the same with dendrobiums – give them the right environment and the basics of a good life and they’ll grow up big and strong and tough and resilient, able to survive all the world can throw at them. When they are in flower you think that anything so exquisitely delicate MUST need hothouse conditions – yet in the wild they grow on trees and rocks, exposed to the elements, surviving drenching rain and drought.
Cooktown orchid (Dendrobium phalaeonopsis)
Ever since I founded the GardenEzi easy gardening Five Step Program (see www.wix.com/jrlakemedia/ezibooks ) I have used the same method for writing most plant articles as I do for my books – breaking it all down into the Five Ps of gardening: Planning, Preparation, Planting, Practice and Protection. So here goes:
PLANNING – Much depends on where you wish to grow your orchid. You may wish to imitate nature and place it on a tree or rock in your garden. More likely, however, you will want to provide it with an artificial growing medium such as a piece of bark fastened to a hard surface, or a cork board, a pot, or a basket. Dendrobiums do best in a position where they have morning sun and light overhead shade, with protection from direct midday and afternoon sun, as well as hot winds, cold winds and (if grown on or near the ground) frost. The Australian “king” or “rock” orchid Dendrobium speciosum will handle temperatures down to zero or even a bit below for short periods, as will the pink rock orchid (Dendrobium kingianum); the Cooktown orchid (Dendrobium phalaeonopsis) will tolerate temperatures down to 50 degrees F (10 degrees C) and so will the popular Dendrobium nobile hybrids. Some of the Asian and Pacific species require higher temperatures and no frost but all dendrobiums cultivated in gardens require night temperatures of no less than 60 degrees F (15.5 degrees C) during their dormancy period in order to flower later. When planning for containers, it’s the size of the maturing stems and leaves that’s important – the root system grows very slowly while you can expect at least one new step a year. Choose a size roughly twice that of the plant and pot (or basket!) on as required.
PREPARATION – If you are growing your dendrobium in a pot or basket (the latter is better) make sure the container is filled with plenty of coarse, fibrous material. You can buy a commercial orchid mix or make your own with coconut fiber or peat moss. If using a pot make sure it is shallow, wide at the base and has at least THREE good-sized drainage holes; put small rocks or pebbles or bits of broken-up terracotta pot in the bottom, to ensure perfect drainage. You can’t pot these orchids using an ordinary potting mix and expect them to do well – they are epiphytes that must develop an extensive mat of roots to survive and grow. They can do this on a wall or rough wooden fence, provided you place them on a slab of bark or cork to start with; in a pot or basket the roots will need plenty of room to spread. I prefer a cane or wooden basket, placed where the roots can grow outside the container on to some other surface when they are long enough, or be easily trimmed back if necessary. Pack the bottom of the basket with sphagnum or peat moss (I once used an old coir doormat, chopped into pieces, with great success!), then add some coarse orchid mix. I usually put in a few twigs and leaf mold from the garden to hold this in place and provide plenty of “open work”; a few small rocks are good too, or a handful of coarse gravel. The idea is to give the roots protection and some initial nutrition while allowing free drainage.
PLANTING – (Or placing!). If you are going to grow your orchid on a tree or rock, tie it firmly in place with any binding material that will rot away as the orchid roots spread and find their own anchorage. NOT plastic, or wire! If you’ve bought it already fastened to a piece of bark or similar, you need only to bind this to the growing place. If it’s in a pot you’ll need to remove it carefully so that the roots aren’t damaged and then bind it in place. The same goes for a division from somebody else’s plant – in both these cases pack sphagnum or peat moss, or soft bark, or burlap (hessian) around the root system and tie the whole lot in place. If you are growing in a pot or basket take the same care in handling the roots and see they are securely in place with the growing medium packed loosely but thoroughly around them. Use the same careful root-handling procedure when potting on, once the plant becomes too large for its container – where necessary cut the roots with a sharp, clean knife. Mature plants can also be divided in this way, increasing your collection.
PRACTICE – In warm-temperate, sub-tropical and tropical climates the dendrobiums readily available to gardeners don’t need to be moved under cover in winter. They all experience a cold-season dormancy period when they produce no new shoots and at this time they require very little water. I usually give mine a sprinkle or spray with a fine mister once a week if the weather is very dry, or if I notice any sign of dessication in leaves or stems. In areas with winter rainfall, overhead protection will prevent the plants becoming too wet for prolonged periods. In summer, when new shoots appear, watering should be regular and plentiful except when it’s raining. Though feeding is not strictly necessary, if you want more and better flowers then apply a half-strength monthly dose of liquid fertilizer. I use a standard balanced mixture in summer to encourage leaf and stem development, switching in autumn to one which is higher in phosphorus and lower in nitrogen, to encourage flower development. This rewards me with superb spring blossoms. Other growers have different methods but there is general agreement on regular light summer and autumn feeding, and no fertilizer at all in the cool season of dormancy. No pruning is necessary but it’s a good idea to remove any withered leaves or canes as these are not only unsightly but may indicate a fungal disease which can spread to the whole plant.
PROTECTION – I never give my dendrobiums any protection at all against insects. Nor have I ever had any problem with fungal diseases. As these orchids grow outside, rather than in a bush or greenhouse, Mother Nature seems to take care of pests. However, like all plants they CAN be susceptible to attacks from insects such as aphids, thrips, scale and two-spotted (red spider) mite. All these can be dealt with by washing down with ordinary dishwashing detergent, though repeated infestations might need a chemical treatment as recommended by your nursery retailer. Rusts can be a problem, showing as reddish-brown marks on the leaves and stems. These tend to occur in long periods of continuously wet weather. You can buy a treatment from your nursery retailer. Other fungal diseases are usually too advanced by the time you notice the effects and it’s mostly a waste of time trying to treat a plant that starts to blacken and rot. The best regime is to make sure your orchids are well-drained, have plenty of air around them, won’t suffer from sunburn (which will scorch the leaves and leave them shriveled and susceptible to fungal attack), and are not exposed to frost, hail or wind.
There is a lot more I could say about growing dendrobiums – especially about propagation and the many different species and varieties available today. But this is enough to get you started – if you want to know more, contact me on my GardenEzi website, or via this blog, and I’ll answer any questions.