I love petunias they are so bright and cheerful, and I easy to care for. For some reason I always thought you didn't have to deadhead them. Matter of fact I'm pretty sure I have been told you don't have to deadhead them. Just plant, water and trim in late summer when the plant gets leggy. You can go about it just this way, I have for many years. But, yes you knew it was coming. Just like most all flowers deadheading will insure you have maximum blooms. I have just started and am already seeing a difference. My understanding is the plant wont get leggy at all if you deadhead. Deadheading petunias, one of those things I should have known and didn't. Oh well live and learn.
“We can complain because rose bushes have thorns, or rejoice because thorn bushes have roses.” — Abraham Lincoln