An Orchidist's Miscellany

LIGHT AND TEMPERATURE


The two factors of growth, light and temperature, have a close relationship, as all those with glasshouses know. Increase light levels, then usually temperatures increase. These two factors are usually difficult to separate. Obviously, these factors have a considerable influence on the photosynthetic activity being completed by the plant.

Some scientific study has been completed looking at the effect of light and temperature on photosynthesis and plant respiration. A plant in the dark showing no photosynthetic activity will show respiration which uses up plant reserves ten times greater at 35 0C than at 10 0C. If the plant measured is maintained at 10 0C, but given increasing light, the balance between photosynthesis and respiration was reached at 200 lux. Above this light intensity, photosynthesis increases to a maximum up to 5000 lux, but then falls off rapidly as the plant leaf becomes saturated.

Studies of the light/temperature balance showed that at the higher temperatures, the more intense the light had to be for the plant just to compensate:

i.e. at 20 0C it was 500 lux
at 25 0C it was 1200 lux
at 30 0C it was 2100 lux
at 35 0C the compensation point was never reached.

The maximum light to reach peak efficiency for any of the lower temperatures was 10,000 lux. The above measurements were completed on Odontioda Lippstadt. The researchers concluded that this plant would grow most efficiently at 15 OC and at 5000-10,000 lux. During the summer sunlight can reach 100,000 lux, so shading is necessary, which also causes a temperature reduction. In winter, when sunlight on overcast days may fall to 500 lux, plants can be kept in respiratory and photosynthetic balance by lowering temperatures to 10 0C.

If the balance between respiration and photosynthesis is not maintained, the plants will grow very little, produces few flowers, and may become susceptible to disease. A positive balance enables maximum growth and flower production to be maintained.

The specific figures given apply only to the plant studied. However, the principles remain the same for ALL plants. A knowledge of a plant's native habitat, and past growing experience intelligently interpreted can give an indication of the conditions necessary to give the balance required

The information indicates that the aim should be to provide as much light as possible, consistent with the amount the plant received in its natural habitat, but with temperatures kept as low as posrible, but again relative to what it receives where it naturally grows. The real challenge for a good grower is to achieve this - as the desired light and temperature levels will always be in conflict to some degree. It is concluded by those who have studied this matter, that increased light, higher humidity and lower temperatures almost always lead to better growth and flowering.

Site established 9th May 1998