Wait until the plant has got 4 or 5 sets of well developed leaves before topping. O.K. about the PH thing - I was just telling you how I did it, you should do what you think is right. I mean it's a weed for crying out loud do you really think the PH of the soil outdoors is the same wherever it grows - that just dosen't seem logical to me. I know I've heard that maintaining a certain PH is good for female plants which seems believeable.