Chapter
5
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Monitoring Temperature
and
Humidity
Gardeners monitor
heat and humidity levels by using thermometers to measure temperature and
hygrometers to measure relative humidity. The desired ranges are:
The 65% point is OK as a rule of thumb, but problems can still occur in the high fifties and low sixties range. Most fungus stop growing when humidity levels are low and there is constant internal circulation from powerful oscillating fans.
Gardeners
sometimes overlook the humidity build-up during the dark hours. Some
growers have their fans set on the same timer as the lights. However this
is the time when molds
are most likely to grow. To prevent attack the fans should
be left on during the dark hours to prevent mold.
Some gardeners use a small heater
to keep the temperature up and the humidity down during the lights’ off
cycle. A dehumidifier serves both purposes, raising temperature and
lowering humidity.
As the temperature drops, the
relative humidity increases. Hot air can hold more water than cold air.
The same amount of water dissolved in cold air creates a higher humidity
than when dissolved in hot air. An automatic humidistat operating a blower
or dehumidifier can be left on during the dark hours. The well-equipped
growth chamber with remote hygrometers and thermometers allows the grower
to observe the conditions in the grow room during the dark hours, without
disrupting the dark cycle.
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