Question
How often should you pinch back wave petunas in a hanging basket to keep them from becoming "leggy"?

Answer
Ann,
I'd cut three or four stems back every week to ten days - do this by taking off a half to two-thirds.  Doing it gradually means that you always have an attractive plant -  you always have some that are rejuvinating, some that are branching out again and starting to bloom further up the plant, and some long ones still blooming.  Be sure to fertilize every two weeks with liquid if you haven't already added time-release such as Osmocote or Proven Winners.

all the best,
C.L.