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by Marilyn H.S. Light
Copyright 1999
HOT CLIMES
Hot, dry desert-like conditions or hot, steamy lowlands can be really tough on plants. What are hot climates really like? What strategies have orchids developed to deal with the environmental challenge of hot climates? How can we growers harness these strategies to our advantage to keep our plants thriving?
How hot is hot?
For orchids, hot means 80-100F (28-35C). Hotter is not better. If growing heat-adapted plants hot, be sure to also provide cooler nights, lots of air movement and shade from intense sunlight.
How bright should the light be?
Unfiltered sunlight or direct artificial illumination can quickly overheat even heat-adapted plants unless there is adequate air movement and some means to diffuse direct light exposure such as cloud and mist, high overhead shade (trees), shadecloth or other barrier to scorching light. Feel illuminated leaves: they should not be hot!
Equitant Oncidiums (Tolumnia) have developed a fan-like arrangement of succulent leaves to reduce the heating effect of sun where they live in the Caribbean. The fan of leaves is aligned such that sun-heating exposure is limited. Also the leaf surface is very much reduced to limit loss of moisture through transpiration. The plants have adapted to a hot day/cooler night situation and to periodic downpours or dew. How should we grow Tolumnias to take advantage of their adaptations?
- Provide high light and warmth by day with good air movement.
- Allow leaf fans to align naturally to light direction. Mark the pot or mount such that the plant remains properly aligned.
- Pot or mount to permit free drainage. Dry between waterings. Vary the humidity between 50-90%.
- Provide temperature variation of approximately 15 F between day and night.
Coelogyne pandurata is at home in steamy coastal regions of Malaya, Borneo and the Philippines. These habitats are not only hot year round but experience cloud cover and daily rainfall. The plants produce very large leaves possibly because they require a lot of light-capture surface given the diffuse light conditions of their natural environment.
- Provide bright filtered light, warmth and good air movement.
- Grow in a large shallow pot or basket to accommodate the plant size and growth rate. Water daily and allow to drain freely. Do not let the compost dry completely.
- Provide temperature variation of 10-15 F between day and night.
HOT HOMES
When it freezes outdoors, we heat the indoors. Dry indoor air is reallytough on heat-loving orchids grown warm. Dry conditions are less problematic if the orchids are kept cool but if they are kept too cool, they do not grow and may even become vulnerable to diseases. What to do?
One possible solution is to grow orchids with a seasonal requirement for heat. Such orchids include those of the lower altitude monsoon regions such as Dendrobium anosmum and Den. loddigesii. These orchids grow when the weather is warm and humid and take a rest while the weather is drier and coolish. The only thing to remember is that the plants should get more light once the growths have matured.
Another possibility is to raise warm-growing Paphiopedilums. Being terrestrials helps a lot in that one can keep the compost moist a lot easier than the surrounding air.
HOT LIGHTS
Lets face it! When sunlight strikes an absorptive object for more than a few seconds that object becomes heated, hot even. Incandescent lights can produce the same effect. Just think how light can heat orchid leaves and think of the damage spot overheating can do even to warmth-loving plants. Air movement helps keep leaves moving and out of danger. Shade cloth, laths, high overhead trees all serve to diffuse direct light. If the relative humidity is low, misting and the resultant evaporative cooling will be very beneficial.
Warmth-loving orchids are not much different from cooler-growing kinds. They simply grow better when it is warmer, especially when there is a variation between day and night temperatures.
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