18 hrs light is perfect veg, just don't veg so long to keep them a more manageable size at finish. Remember, most strains add another 2/3 in size while in flower! But Shov is right about the sativas. But most of the sativa strains found have at least a little indica in them to speed them up, make them shorter, denser & faster. I think pure sativas are a pain in the ass indoors! I'll leave lugging around the big pots to Shovel, he's not afraid of those big tall ladies. I'm only 5'2" & they just beat me up!