Grow cool, grow outside!

by Gab van Winkel

Images: Eric la Croix

Do you know that envious feeling when you get photographs from friends who live in the tropics? Especially those pictures from their garden, where orchids grow outside, in a tree or on the veranda, and apparently with little attention, because ‘we do have some rain as well, you know’.

The beautiful Laelia anceps has many colour forms

Do not despair - you too can grow tropical orchids in your garden - that is, in the warmer half of the year and by a careful selection of plants. In southern and central parts of Britain, as in the Netherlands where I live, summer weather is ideal for cool-growing orchids. Often, such species are considered as 'difficult' by people who grow them in a greenhouse, but once put outside they flourish.

Go high

Where do such 'cool' species come from? Some are found in temperate regions such as Japan and south Australia, but for most species you must go high up on the mountains of the tropics. Even if 95% of tropical orchids grow in intermediate to warm conditions, there are still hundreds of species that prefer to be cool.

Mountain climates are always characterised by a steep temperature drop at night, strong air movement and high rainfall, but there are differences. Many equatorial mountain forests, such as those in central New Guinea and Colombia, have a year-round cool, very wet climate. Here, an altitude of 2,000m is a safe limit; if a species, according to literature, has most of its elevation range above that, you may consider it as cool growing. Further away from the equator, for example in the Himalaya or Mexico, 1,500m is high and cold enough. Many of these regions have a seasonal climate with wet, rather warm summers and dry, cool winters. At high altitudes, however, mist and morning dew provide moisture even during the 'dry' season. Only deciduous species require a really dry winter rest.

Rain or shine

Often, our plants can be put outside as early as April, as soon as night temperatures stay above 5°C, but if there are frosty nights or long periods of chilly days they are better brought in again. By the middle of May, night frosts should be over and normally our plants can stay outside until October. When the autumn weather turns really bleak, they must be returned inside.

Outside, we must help our orchids to survive the weather, rain or shine. Plants in plastic pots will, at some point, be blown away, so it is better to use clay pots, and attach hanging plants firmly to their tree or fence. Rainy weather can last for days, therefore use a very coarse, airy medium that retains little moisture. This will require daily watering during dry weather, but in my experience such a diurnal wet-dry cycle greatly stimulates root growth. Species that start their cool, dry rest in autumn should be protected from rain then, for example by a sheet of glass.

The typical problem with greenhouses is that you can only exclude heat by excluding light. When grown outside, species that require strong light or even full sun, can have that without heat stress. Also species that need shade grow more compact and sturdy. Other advantages are the constantly fresh and moving air and the much larger temperature drop at night. Many species need that to induce flowering.

Trained toads

In the garden, snails and slugs pose by far the greatest danger. Young shoots, flower buds and root tips can be decimated overnight, even if that requires a two metre climb! Some chemical control is certainly needed. Plants are best placed on 'islands' in large trays filled with water. Still, unless you have a couple of trained toads, you should supplement these measures by regular nightly inspections by torchlight.

During winter, our plants can stay in a greenhouse, which will need far less heating than the average orchid house. But a plus of growing 'cool' orchids is that a greenhouse is not really needed. A cool bedroom is suitable, as long as there is plenty of light and fresh air. My plants winter in a large attic with high windows. Central heating pipes running full-length keep minimum night tempera-tures above 5°C (mostly around 10°C). Ideally, day temperatures are ten degrees higher. The water-filled 'anti-snail' trays provide extra humidity. Last year I installed 400 W of fluorescent tubes to keep the day length at 13 hours, and a medium-sized fan. Already after two months, plants have responded visibly.

Refreshing

Our colleagues in Australia and New Zealand discovered the advantages of 'cool' orchids more than ten years ago. They try, for example, to improve the cold tolerance of Phalaenopsis hybrids by crossing with Australian Sarcochilus species. Even as far south as Melbourne, dozens of species are grown in an open 'bush-house' without any extra heating.

As yet, this refreshing trend has hardly reached Europe, Britain and North America. How much gas or oil do you burn to keep your greenhouse at 16°C during winter? If you do not have a greenhouse and want to expand your orchid collection, consider growing outside. It is certainly rewarding and as close as you can get to living in the tropics!

 

Advantages of growing outside

• Sturdy, healthy plants that are eager to flower
• No 'greenhouse pests' such as spider mites and whitefly
• No need for a greenhouse (if you have some cool window-sills available)
• Much lower heating costs

Disadvantages

• Smaller plant choice and often poor availability
• Thorough investigation necessary, in literature and on the internet, to determine if a certain species can be grown cool (which also yields valuable information on habitat and culture)
• Control of slugs and snails necessary
• Having to move your plants at least twice a year

Aerangis mix-up

When growing 'cool' orchids, you often find yourself hunting for those one or two high altitude members of a popular genus, which are usually poorly available. Two years ago, I was delighted to find a nearby nursery that offered Aerangis thomsonii, the coolest growing species of this elegant genus, occurring at altitudes of 1,600-3,000m in East Africa. The four seedlings I bought seem to like the Dutch summer weather and grow slowly but steadily.

I learned that the plants were originally raised by Jan de Graaf, a senior member of the Dutch Orchid Society. Then, in October 2003, Jan told me that the first of the seedlings he raised had flowered and turned out to be Cyrtorchis arcuata. The capsule had been collected six years earlier by a friend of his near Kericho, Kenya, from a tree covered with both species. Apparently, in the tangled mass of plants a mix-up had taken place. About 150 of these misnamed Cyrtorchis arcuata seedlings are now spread among nurseries and amateur growers in western Europe and Britain.

True Aerangis thomsonii is probably not available at the moment. The good news, however, is that these Cyrtorchis arcuata seedlings from Kenya represent a high altitude form of this variable, beautiful and adaptable, species.

Still, I must admit, I was not amused to 'lose' an Aerangis. So, if you happen to know of Aerangis thomsonii or Aerangis montana (another unavailable high altitude species) on offer, please let me know.

Plant choice

The following species grow well in my garden during summer.

Ada aurantiaca	Colombia	1,500-2,800m
Angraecum magdalenae	Madagascar	around 2,000m
Bletilla striata	China, Tibet, Japan	1,100-3,200m
Bletilla ochracea	South China	900-2,400m
Calanthe discolor	South China, Japan	700-1,500m
Coelogyne cristata	East Himalaya	1,500-2,100m
Cymbidium floribundum (pumilum)	South China, Taiwan	100-3,000m
Cyrtorchis arcuata	Africa	0-3,000m
Dendrobium gracilicaule	East Australia	up to 1,000m
Dendrobium moniliforme	Japan, Korea, China, Taiwan	up to 3,000m
Dendrobium speciosum	East Australia south to Victoria
Dendrobium subclausum	New Guinea	1,500-3,200m
Dendrobium victoria-reginae	Philippines	1,300-2,600m
Dendrochilum javieri	Philippines	1,800-2,400m
Dockrillia (Dendrobium) teretifolium	East Australia
Euchile (Encyclia) citrina	Mexico	1,300-2,200m
Jumellea rigida	Madagascar	around 2,000m
Laelia anceps	Mexico	1,300-2,600m
Lycaste aromatica	Mexico, Honduras, Guatemala	900-1,500m
Masdevallia veitchiana	Machu Picchu, Peru	2,200-3,000m
Neofinetia falcata	China, Korea, Japan
Osmoglossum (Odontoglossum) pulchellum	Central America	up to 2,600m
Paphiopedilum armeniacum	Yunnan China, Burma	1,400-2,100m
Papilionanthe (Aerides) vandarum	Northeast India, Burma	1,200-1,500m
Phalaenopsis wilsonii	South China	800-2,200m
Pleione formosana	Taiwan	500-2,500m
Pleione praecox	Nepal to north Laos	1,200-3,400m
Polystachya bella	Kenya	around 2,000m
Prosthechea (Encyclia) vitellina	Mexico, Guatemala	1,500-2,600m
Sarcochilus hartmannii	East Australia	up to 1,000m
Sedirea japonica	Japan
Spathoglottis ixioides	East Himalaya	around 3,000m
Thunia alba	East Himalaya, South China, Malaysia	1,000-2,300m
Vanda coerulea	Northeast India to south China	800-1,700m

 
Gab van Winkel started growing orchids 25 years ago as a university student. With his two young sons, he now lives in Utrecht, the Netherlands, where their garden is devoted to vegetables and orchids. Questions and comments can be redacteur@nov-orchidee.nl

Literature

Chen Singchi, Tsi Zhanhuo, Luo Yibo (1999). Native orchids of China in colour. Science Press, Beijing.

Cribb, P J & I Butterfield (1999). The genus Pleione. Royal Botanic Gardens, Kew.

Hawkes, A D (1965). The encyclopaedia of cultivated orchids. Faber and Faber, London.

la Croix, I F & E A S (1997). African orchids in the wild and in cultivation. Timber Press, Portland.

Lavarack, B, W Harris & G Stoker (2000). Dendrobium and its relatives. Timber Press, Portland.

Lavarack, B, W Harris et al. (2002.) Botanica's Orchids. Laurel Glen Publishing, San Diego.

McDonald, R (1994). Cool-flowering orchids. New Zealand.

Pridgeon, A (1992). The illustrated encyclopedia of orchids. Timber Press, Portland.

Upton, W T (1999). Sarcochilus orchids of Australia. Double U Orchids, Sydney.