I don't have mine on and I don't think it is necessary...but would imagine it wouldn't do any harm, kind of like wind not stopping when the sun sets if it was grown outdoors.....but I'm pretty new to this
yeh its fine to leave the fan on,,,i leave mine on 24/7,,,mine are flowering now and having a fan on in ya grow room helps prevent mold,it also helps the air circulate and keeps it fresh plus it strengthens stems.peace
its better to leave the fans on at night. the plants will continue to grow, as they are using atp created during the day to produce plant matter late into the night. It will also help prevent molding issues and other diseases.
LIke everyone else said, keep em on always. Great circulation, makes the babies more strong. I've found if you can set your fans so they get a good shake, and then by the time it comes back to them they have stopped moving, hit em again with the wind. Really makes the plant to become more sturdy being shaken lightly four-five times a minute.
That said, you don't want them blasting the plants either... just a nice little shake and then return to still, and repeat. Works great for me.
not sure if this is entirely true but it came from my grower friend in humboldt so maybe it holds some water. You should leave your oscilating fan on 24/7 to keep the co2 circulating in the room but i'm not sure if this is just in general or because he may have a c02 setup in his grow room.
since it was mentioned... as far as i know... plants switch modes at night time and no longer need co2 (so shut that down for sure) ... they actually start to use oxygen during the night cycle and to release co2.