GrowCNanswered grow question 3 years ago I switch depending on how large I want the plant to get. I generally figure the plant will double in size during the stretch. So, look at the size of your plants and the size of your grow area and let that say when to flip. I most often use a 36" x 36" (90cm x 90cm) grow tent. If growing four photo period plants I might flip at 4-6 weeks. If growing only one plant in the same space I will veg much longer, aiming to fill the tent when the plant is mature.