Flower at 18 - 24 inches. At that height with the proper lighting, feeding, watering and air circulation/venting you could average and ounce a plant or better depending also on strain. I would go for an Indica as they flower and finish sooner the Sativas, Northern Lights is a good indoor grow though I doubt you will find a pure vareity of that strain. You do not want to go to high with your plants as this may create difficulty with your lighting and the heat from the lamps. You should maintain a distance of 18'' or so from lamps to tops and don't want your fixtures cramed to close to your ceiling. Also, with plants that tall you will get little light to the bottom growth ending up with skimpy, whispy flowers that amount to little or nothing. Go 18-24, use the bottom growth for cloning just before you begin to flower and snip the rest to about six inches from medium leaving a clean stalk at the bottom. Prune at 8-10" for additional tops, flower 18-24, no feeding last 21 days, check resin glands with microscope just before harvest, Bon Apetite!...yesca
