GROW ROOM TEMPERATURE
is one highly variable factor. Most books state optimum grow
temperature to be 70-80 degrees, but many list extenuating
circumstances that allow temperatures to go higher. Assuming
genetics is not a factor, plants seem to be able to absorb more
light at higher temps, perhaps up to 90 degrees. High light and
CO2 levels could make this go as high as 95 degrees for
increased growth speed.* An optimum of 95 degrees is new data
that assumes very-high light, CO2 enrichment of 1500 ppm and
good regular venting to keep humidity down. It is not clear if
these temperature will reduce potency in flowers. It may be a
good idea to reduce temperatures once flowering has started, to
preserve potency, even if it does reduce growth speed. But
higher temperatures will make plants grow vegetatively much
faster, by exciting the plants metabolism, assuming the required
levels of CO2 and light are available, and humidity is not
allowed to get too high.
With normal levels
of CO2, in a well vented space, 90 degrees would seem to be the
absolute max, while 85 may be closer to optimum, even with a
great deal of light available. Do not let the room temperature
get over 35 C (95 F) as this hurts growth. Optimal temperature
is 27-30 C (80-86 F) if you have strong light with no CO2
enrichment. Less than 21 C (70 F) is too cold for good growth.
at night are OK down to about 60 degrees outdoors, then start to
effect the growth in a big way. Mid 50s will cause mild shock
and 40s will kill your plants with repeated exposure. Keep your
plants warm, especially the roots. Elevate pots if you think the
ground is sucking the heat out of the roots. This is an issue if
you have a slab or other type of cold floor.
goes up, so does the ability of the air to hold water, thus
reducing humidity, so a higher average temperature should reduce
risk of fungus.
Contrary to many
reports, high humidity is not good for plants except during
germination and rooting. Lower humidity levels help the plant
transpire CO2 and reduce risk of molds during flowering.
the potency of buds goes down as the temperature goes up, so it
is important to see that the plants do not get too hot during
* D. Gold: CO2,
Temperature and Humidity, 1991 Edited by E. Rosenthal.