Many professional growers successfully cultivate cannabis outdoors, but these plants are subject to the weather. They may receive too little or too much rain, very little sunlight on overcast days, and a battering of wind and rain during violent storms. Also, they are far more prone to attack from marauding insects and thieves.
Although cultivating in a grow room is significantly more expensive than outdoor growing, you can customize the indoor environment to produce the highest possible yields of the best possible grade of cannabis. Aside from the growing medium and lighting that you choose, there are five key factors that must be carefully controlled: circulation, carbon dioxide (CO2), ambient air temperature, humidity and ventilation.
Circulation: Maintaining continuous circulation of the surrounding air is important to the health and growth of cannabis, since your plants use all the CO2 surrounding their leaves within just a few minutes. Unless the stale air is constantly replaced with fresh air, a “dead air zone” quickly forms around the leaves, which stifles their pores (called “stomata”) and halts growth. So, growers will install one or more oscillating fans in the room. The constant breeze has the added benefit of strengthening the plant’s stems so that they are better able to support large, heavy buds.
CO2: As with any plant, cannabis needs to breathe in carbon dioxide. The air in a grow room commonly contains a mere 0.03 to 0.04 percent CO2, but cannabis can absorb as much as 0.12 to 0.15 percent. Plants can be “supercharged” through CO2 generators, which increase the growth rate by as much as 30 percent. However, CO2-enriched plants require significantly more care because they will use space, water and nutrients faster than non-enriched plants.
Temperature: Keeping room temperatures from 75° to 80° will also stimulate a more rapid metabolism in supercharged plants. If the temperature is allowed to climb above 85°, CO2 enrichment ceases to become effective. And above 90°, plant growth halts altogether.
Humidity: When the humidity in the room is high, water slowly evaporates from the plant’s leaves. The stomata close, transpiration of moisture slows and plant growth is reduced. So, the humidity shouldn’t be too high. During the seedling and vegetative stages, plants grow best when the humidity is between 60 and 70 percent. During the flowering stage, keep it between 40 and 60 percent. Because a 10-square-foot garden can transpire 10 to 50 gallons of water per week, install one or more dehumidifiers or air conditioners to reduce the humidity level.
Ventilation: Finally, provide your grow room with adequate ventilation to help control temperature, humidity and CO2 for your plants. When designing a ventilation system, remember that an exhaust fan is able to pull air out of a room four times faster than a vent fan is able to push it into the room. So, it’s good to buy an exhaust fan that can replace all the air in your grow room within five minutes or less.
Centrifugal exhaust fans, which are rated according to the number of cubic feet of air per minute that they move, are very efficient. But these types of fans require both intake and exhaust vents. So, to prevent unwanted insects from entering and unwanted odor from escaping, place activated charcoal filters at each end.
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