Orchid Temperatures

Orchids are shade-loving plants, and while they are growing they need the equivalent of the dappled sunlight they would receive growing in the tree canopy of their natural home. Too much light during the summer will harm the plants by turning the foliage a light green-yellow.

A useful piece of equipment is a maximum/minimum thermometer, or even several, which can be placed close to the orchids and the temperatures noted. In a greenhouse, it becomes difficult to grow orchids from these three ranges together in one place. What suits one group will not suit another, and you will find that inevitably some orchids will suffer from being too cold or too warm. An ideal situation is to divide a greenhouse into two or three sections, depending upon which orchids you wish to grow.

Insufficient light, on the other hand, will create dark green leaves that can become over-extended and limp. The aim should be to give your orchids just enough light to produce a good mid-green, healthy foliage and pseudo bulbs that will develop flower spikes at the right time.

After flowering and before the new growth starts, Calanthe pseudobulbs can be taken out of their pot and left to dry until the new growth is seen.

The summer daytime maximum should not exceed 30C (86F), which is a comfortable temperature for the orchids. Above this, the plants will inevitably become stressed, and growth will slow down and may even come to a stop. Overheating can be difficult to prevent in a greenhouse and needs to be controlled by sufficient ventilation, shading and damping down.

Moving the orchids to a lighter area winter may be the answer, provided their temperature requirements are the same. Alternatively, electric light using horticultural fluorescent tubes above the orchids, may be the answer. However, this system requires a considerable financial outlay to be satisfactory. It grows well in colder climates and is used is northern North America with success.

The intermediate orchids, which include the showy cattleyas and the handsome, shade-loving paphiopedilums, require a winter night-time temperature that is 3C (5F) higher, giving a minimum of 13C (55F) at night. Wherever possible, there should be a higher temperature by day, but this should not exceed 310 C (86F). Again, temperatures on either side of these recommendations bill cause the plants considerable stress, and over a prolonged period can cause their eventual demise.

At this time, the glass should be cleaned of any paint shading or green algae to ensure that the orchids receive all the available light. This will also add considerably to the temperature on sunny days, thus saving on the artificial heating.