Marijuana Grower's Handbook - Part 1 of 33
"Marijuana : The Plant"
from
Marijuana Grower's Handbook
[Indoor/Greenhouse Edition]
Ed Rosenthal
"Temperature"
Marijuana plants are very hardy and survive over a wide range of temperatures. They can withstand extremely hot weather, up to 120 degrees, as long as they have adequate supplies of water. Cannabis seedlings regularly survive light frost at the beginning of the season. Both high and low temperatures slow marijuana's rate of metabolism and growth. The plants function best in moderate temperatures - between 60 and 85 degrees. As more light is available, the ideal temperature for normal plant growth increases. If plants are given high temperatures and only moderate light, the stems elongate. Conversely, strong light and low temperatures decrease stem elongation. During periods of low light, strong elongation is decreased by lowering the temperature. Night temperatures should be 10-15 degrees lower than daytime temperatures. Temperatures below 50 degrees slow growth of most varieties. When the temperature goes below 40 degrees, the plants may experience some damage and require about 24 hours to resume growth. Low nighttime temperatures may delay or prevent bud maturation. Some equatorial varieties stop growth after a few 40 degree nights.
A sunny room or one illuminated by high wattage lamps heats up rapdily. During the winter the heat produced may keep the room comfortable. However the room may get too warm during the summer. Heat rises, so that the temperature is best measured at the plants' height. A room with a 10 foot ceiling may feel uncomfortably warm at head level but be fine for plants 2 feet tall.
If the room has a vent or window, an exhaust fan can be used to cool it. Totally enclosed spaces can be cooled using a water conditioner which cools the air by evaporating water. If the room is lit entirely by lamps, the day/night cycle can be reversed so that the heat is generated at night, when it is cooler out.
Marijuana is a low-temperature tolerant. Outdoors, seedlings sometimes pierce snow cover, and older plants can withstand short, light frosts. Statistically, more males develop in cold temperatures. However, low temperatures slow down the rate of plant metabolism. Cold floors lower the temperature in containers and medium, slowing germination and growth. Ideally, the medium temperature should be 70 degrees. There are several ways to warm the medium. The floor can be insulated using a thin sheet of styrofoam, foam rubber, wood or newspaper. The best way to insulate a container from a cold floor is to raise the container so that there is an air space between it and the floor.
Overhead fans, which circulate the warm air downward from the top of the room also warm the medium.
When the plants' roots are kept warm, the rest of the plant can be kept cooler with no damage. Heat cables or heat mats, which use small amounts of electricity, can be used to heat the root area. These are available at nursery supply houses.
When watering, tepid water should be used. Cultivators using systems that recirculate water can heat the water with a fish tank heater and thermostat. If the air is cool, 45-60 degrees, the water can be heated to 90 degres. If the air is warm, over 60 degrees, 70 degrees for the water is sufficient. The pipes and medium absorb the water down a bit before it reaches the roots.
Gardens using artificial lighting can generate high air temperatures. Each 100 watt metal halide and ballast emits just a little less energy can a 10 amp heater. Several lights can raise the temperature to an intolerable level. In this case a heat exchanger is required. A venting fan or misters can be used to lower temperatures. Misters are not recommended for use around lights.
Greenhouses can also get very hot during the summer. If the sun is very bright, opaquing paint may lower the amount of light and heat entering the greenhouse. Fans and cooling mats also help. Cooling mats are fibrous plastic mats which hold moisture. Fans blow air through the mats which lowers the greenhouse temperature. They are most effective in hot dry areas. They are available througn nursery supply houses.
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everything I find on low temps say the same thing
low temperatures slow down the rate of plant metabolism
this tells me the plant cant uptake nute's as well if temps are below 60*.... How is pumping more P to it going to help if it cant metabolism it?
last winter my grow room got down to 55 and no matter how much 0-50-30 I gave it made NO diff in the plant growth.... sure I got a crop but not like I do when temps are up around 75*
pink and purple can also be a pheno trait like the POG I grow
and has nothing to do with cool temps.
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