Trim back the petunias and fertilize them. They'll come back into bloom in a couple weeks or so. You just want to trim off the old flowers so they stop going to seed, then they'll set new flowers.

They're already in, you might as well use them. They'll last into fall but not late fall.

Dahlias will bloom until frost, but any rain and they're toast. Well, slime and broken stems actually.

I'm assuming this is full sun if you planted petunias.

Thanks for the response. Your right,, I might as well use them like you said since they are already there. I've been trying to deadhead them all along but its impossibe now, there are so many!!! I'll try cutting them back like you suggested!! Thanks again! Mary