Professional Marijuana Grower November-December 2018 Issue | Page 41

before the plants can use it. Ideally, air should not be
exchanged in and out of a grow room. If you have an
air-cooled refl ector, the air drawn through the fan to
cool the bulb must enter and exit the grow area without
coming in contact with the air in the grow room. Sealing
the grow space allows plants to more completely use the
CO 2 that is enriching the environment. During the night
cycle plants actually give off CO 2 which causes a grad-
ual increase in CO 2 levels until the lights come on and
the plants resume absorbing CO 2 . You can save CO 2 by
waiting an hour or so into your daylight cycle to turn on
the CO 2 device.
Air Circulation
Typically an indoor grow room will have wall mounted
oscillating fans blowing back and forth with no real
‘direction’ of the air. A greenhouse uses Horizontal Air
Flow or HAF which is fans mounted above the canopy
that create a directional fl ow. One side of the green-
house will have the fans point in one direction while the
other side of the house will have the fans blowing in the
other direction. This creates a vortex of air movement
that is more effective than an oscillating fan.
volume of air in a medium to large greenhouse can be
estimated by multiplying the fl oor area times 8.0 (the
average height of a greenhouse).  In winter, 20% – 30%
of one (1) air volume exchange per minute is suffi cient
for mixing in cool air without chilling the plants.
CO 2 Enrichment
CO 2 enrichment in greenhouses allows crops to meet
there photosynthesis potential. Enriching the air with
CO 2 can be done by means of the combustion of natural
gas or with liquid CO 2 . The supply of extra carbon diox-
ide is an often applied method to increase the yield of
greenhouse crops. The amount of carbon dioxide in the
outside air is, depending on your location, 350 parts
per million. This amount is suffi cient for plants to grow,
however when a high number of plants are placed in
a greenhouse, the carbon dioxide levels drop as all
plants are using carbon dioxide for photosynthesis. By
adding CO 2 (CO 2 enrichment), it is possible to increase
the photosynthesis potential of the crops, especially on
sunny days. Keep in mind that yields will only increase if
CO 2 is a ‘limiting factor’. This means that if all the other
variables are not optimal (light, fertilizer, temp/humidity,
pH, etc.) you will not achieve the benefi ts of increased
CO 2 levels.
CO 2 enrichment will not be as effective if the grow
area is not sealed because the CO 2 will be exhausted
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Professional Marijuana Grower • 41