Certified GKH Gardening Expert
These plants do benefit from getting a bit of a trim a few times during the summer. Normally, you should take off 1/3 - 1/2 of the plant if you start to notice it getting leggy. This will force them to bush out again, though you will lose blooming for a week or two. I normally trim mine right before I leave for vacation. That way I don't see the plants looking bare and by the time I get back, they are starting to bloom again.