I wouldn't say it NEEDS it, but I let my ladies sleep. I was going to see if I could time it right to leave them outside on their own to veg for a bit more and then naturally flower in the beginning of summer but I got lazy. There is a certain few weeks in socal that you can veg outside without them automatically going to flower. we actually had one we threw outside at the onset of winter and it started to flower and then flipped back to veg and reflowered once it started getting warm again.