Hydroponics Growing plants with their roots in a nutrient solution rather than soil. Also called hydroponic Read more about Hydroponics Leaf Doctor Purple stems and petioles: the phosphorus myth Purple stems are not a reliable sign of phosphorus deficiency. Leaf Doctor Yellowing lower leaves: what it is, and when it’s nothing Before anything else: if you're six or more weeks into flower and it's only the bottom leaves, this is probably normal.