I love physically manipulating cannabis. Pinch, top, FIM, lst, super crop and just about anything else you can think of. One thing I haven't tried yet is seeing if I can espalier them like a fruit tree and I will give it a shot at some point. I doubt they can be coppiced but it sure would be cool to try. I don't know where but I recently read an article on actually pinching out a small piece right off the top of an actively growing bud. Well I'm giving it a shot as it's supposed to increase the yield but who knows.
One thing you can count on is that your girls are just going to love the COBS. Other than the sun I've never seen anything like it.
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Make them do what you want. I have a budski that swears by root pruning. Haven't tried that yet either but I will.