This summer I determined I was going to figure out how to handle them. I have a neighbor who has such beautiful petunias and I asked her how she did it...She said whenever they look scraggly she just hacks them back. Then I read about a technique of cutting them back one third at a time, so you are never left with completely sheared plants. So I have been trying this technique and so far, so good. Will keep you posted.
Petunias