Gerry I usually dead head my annuals especially the petunia's. Most annual and perennials will re bloom for you if you dead head and trim them back after the blooms are ready to fall away. Hope that helps.
Even if plants don't re-bloom, Gerry, it's generally a good idea to deadhead. Washington State University has the whys and the how-tos here:
I compulsively deadhead. Marigolds, petunias and geraniums will rebloom and fill out if you keep at it. it's gotten so that when i visit other places and they have ratty geraniums i get itchy fingers and need to "groom" them.