by Greg Green
During vegetative growth and flowering, cannabis plants love to get fresh air. Always keep a window open and let your grow room refresh itself every day. The fresher the air the better. Also during the dry periods, in between watering, the roots like to breathe. Fresh air is always the best air. During winter you may want to reduce the time you leave the windows open as the cold may stunt growth. Just refresh the air in your room for 15 – 20 minutes during winter and close it again.
If your grow is enclosed, then use fans to extract the old air and another fan intake to refresh the system.