Another tip for petunias is when the flowers die to cut/ pull them off ( unless you want them to go to seed) Pulling the flower stem off of the plant will cause it to form more blooms because it didn't get to make seed. You will see the 'link' at the base of the flower stem where it can come off. They usually snap off at this joint easily. ( Lol, Not the exact botanical terms, But you will see what I mean :))