When temperatures rise above 78
degrees, cannabis’ rate of growth slows
once again as the plant uses part of its
energy to dissipate heat and keep its water
content constant. The rate of growth
continues to slow as the temperature rises.
Photosynthesis and growth stop
somewhere in the 90’s.
When the lights are off, photosynthesis
stops. Instead, the plants use the sugars
and starches for energy and tissue building.
The plants do best when the temperature is
lower during this part of the cycle. The fact
that the lamps are off will lower the
temperature quite a bit, and ventilation can
be used to cool the space down.
Looking at a marijuana leaf under a
magnifying glass, a viewer will notice that
there are small "hairs" covering it. These
appendages form a windbreak which slows
air movement around the leaf. This helps to
modify the temperature by holding air which
has been warmed by the tissue surface,
similar to the way hair or fur keeps warm air
trapped near the skin.
Since plants transpire water, the air
surrounding the leaf surfaces is more
humid than the air in the surrounding
environment.
Outside, there is usually a breeze so
that air is ventilated from the surface. The
breeze removes waste gasses and
humidity and brings fresh air containing
CO 2 in contact with the surface.
Indoors, air movement is easily
achieved using fans. The movement should
be swift but not forceful. Leaves should
have slight movement. Oscillating fans are