Answer: If you want to encourage better branching, pinch them lightly early in the growing season. Flower buds form on the ends of branches; pinching too late may delay blooms. Otherwise, they shouldn't need pruning unless they grow too large for their space. Once the new shoots have emerged the next season, you can prune out any old stems. I'd leave the tallest stem alone (3' high is a little too high for new branching and if you cut it down too low, it may not bloom for you), but you can pinch out the tip of the 12" branch so you can study just how your plant will branch after pruning. The entire plant will look sparse this year but next year it should produce lots of new stems. If you pinch out the growing tips when they reach 12" in height, you'll have a thick, dense plant with lots of flowers.
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