They continue to bloom but not as vigorous....it takes energy to make seed. Everyday I go by mine and pinch out all the fading blooms before they make pods :D

Vera

I cut my petunias back to a few inches and they grow back beautifully. Actually I just did that this morning. I prune many of my plants, especially annuals, as they start getting leggy this time of year.
Karyn

I never cut petunia's back. They don't get leggy because every time you pinch out the flowers (clear back to the stem...not just the petals) you are encouraging branching and more flowers.

Vera

I mowed a row of petunias down a couple of years ago (they looked like they'd pretty much had it) and they sprang back to life with gusto. Got all green and bushy and kept blooming through fall.

While we're on petunias, do the seeds need anything special? I collected an envelope full from my mom's petunias yesterday and just dumped them out on a paper towel.

I don't do anything to my Petunia seeds. I leave them alone until everything dries up then scrunch up the pods and that part..whatchamacallit..that part that holds the pod... so that I can separate the seeds from the pods, etc. Nothing to it. :-)

I usually trim my Petunias down just because I don't always feel like pinching them, particularly the way they grow in certain spots of my yard. They never seem to resent it.

I pinch the flowers on certain ones that I'm paying closer attention to and they just keep blooming. The ones I pinch are usually smaller plants than the others.
(This is just what I do, not for any special reason, not because I know some rule...I just do it. Neither activity seems to hurt the plants at all).

Linda