GMSgrowsanswered grow question 3 years ago The 20 hour light schedule is part of the culprit here. Plants do a lot of growing in the dark, and if this is a photo period plant, then she really likes her 6 hours sleep. I usually switch my photos over at 18 to 24 inches. That will give you a plant from 4 to 6 ft. usually, when she is done her stretch..