When other conditions are
correct, the rate of photosynthesis doubles for each 10OC (18OF)
rise in temperature. This principle applies within the 10-30OC
(50-86OF) range for temperate plants and 15-35OC
(59-95OF) for tropical plants.
When growing in an enclosed area such as a
grow room or greenhouse, air temperature is commonly controlled via
artificial heating, ventilation or
Day time: The optimum daylight
temperature is around 25OC (77OF). Never allow the
temperature to exceed 30-35OC (86-95OF) otherwise
“photorespiration” can occur. This results in the wasteful destruction of
which slows growth rates. When the temperature is too low (i.e. below 25OC
/ 77OF), the rate of
photosynthesis and respiration will
be suppressed. This will restrict essential plant processes and growth.
Low temperatures can also cause
humidity to increase to levels that can promote
disease problems. Cold leaves will suppress
transpiration rates which in turn restricts nutrient uptake.
Translocation is also a lot slower when the temperature is below optimum
which causes systemic agents (e.g. foliar fertilizers) to act slower.
Night time: The respiration rate needs
to be suppressed at night by allowing the
temperature to drop to at least 20OC (68OF).
“Day time” respiration rates are wasteful at night because less ATP energy
is required. ATP energy is the product of respiration. During the day
time, more ATP is required for processes such as downloading sugars and
nutrient uptake which occur during photosynthesis. Plants do not
photosynthesise at night which means less ATP energy is needed. Because
plants cannot store ATP, any excess that is produced is wasted.