Chapter 16

CARBON DIOXIDE

Carbon dioxide (CO 2 ) is a colorless,

odorless gas found in the air. Under normal
circumstances, including the conditions
growers deal with, it is totally harmless.
Each molecule consists of one part carbon
and two parts oxygen. CO 2 is often

generated in the home. When a stove or
water heater bums gas it produces water
vapor and CO 2.

Plants use CO 2 as a raw material during

the process of photosynthesis. CO 2 is

quickly used up in a well lit enclosed space
Until it is replaced, the process cannot
continue. The availability of CO 2 to the plant

can be a limiting factor in photosynthesis
and plant growth.
Keeping the door or curtain of a small
grow room open helps tremendously
because a whole side of the grow space is
exposed to external air. An open door in a
large a room gives a much smaller ratio of
interface, since the percentage of the
perimeter serving as a vent is much
smaller.
CO 2 constitutes about .03%, or 300

parts per million of air in country areas and
about .035 - .04% in industrialized regions.
Photosynthesis and growth could proceed
at a much higher rate if the amount of CO 2

available were increased to about .15% or
1500 parts per million instead of the .035 -
.04% found in urban areas. Higher