I am also growing grandmommy purple from herbies. Toward the end of veg i had some deficiencies that turned the leaves white and the leaves would eventually die. So i topped dressed some gaia green 444 glacier Rock dust and power bloom with some Epsom salt and earth worm casting and just flipped it to flower. I am pretty sure the deficiency came from using just plain ro water but that is just a guess, but now I am using spring water and i sprayed the leaves with Epsom salt until i got those first flowers. I think i stunted the growth in the stretch faze of flower by not giving it no time to recover from the deficiency so now the plant is aout 20 inches or so but honestly I never measured it. But now it is strong praying towards the light and giving off a nice little smell and nodes are stacking nicely in preparation to make some fat buds. All this and I really trying to say watch at around the 9 or 10 week into veg. This plant wants a lot of magnesium and all the trace minerals that come in spring water.