I mainly use this technique for re-vegging, but the technique is sound and versatile. Will make shitloads of cola's on her for re-flowering, (kinda like the results of a successful FIM) or you can keep her in veg as a mom for clone shoots. Very effective once mastered. My main intent here was to give a sort-of pictorial essay of what stinky said. :thumbsup:

If you do this after switching to 12/12, it will stunt vertical growth. She'll likely yellow a tad (slight lockout from freshly severed roots, I assume) till she get's her bearings. Careful not to spray severed branch-ends till completely dry, too.

Also, for the first couple of weeks, it will fill-in much more than it will stretch. (If you've ever broke a cola during flower, you'll recognize the growth habit...) Will suffer in the yield dept, too.

Have you tried to adjust length of veg time to compensate for flowering problems?