When has a plant stopped veg and start flowering ?what are some indictators ?

Hi there.. when the white pistils (actually it's the stigmas) are showing, then this means that the pre-flowering has happened, which basically means your plant has reached maturity and has shown the sex.. in the case of the sigmas it means it's a female. This does not yet mean that she's flowering. Especially in photoperiodic strains this is important, as preflower still happens, even when the plant hasn't been put into a 12/12 cycle yet. When the plant is put into 12/12, or if the plant is an autoflower and the flowering period begins (the first flowers start forming on top of the plant), they will first go through a stretching phase, in which some strains can get even 3 to 4 times taller than they were before. This is normal and most likely what confuses you now a bit. During this stretching phase it's best to still give the plant vegetative nutrients, as they are higher in nitrogen, which is something the plant still needs at this time. Only after the stretch has finished, and the plant fully focuses on creating and fattening up the buds, it's best to use the bloom-nutrients (which are high on P and K) as then nitrogen isn't needed much by the plant anymore. happy growing