Help! The blossoms on my "low maintenance" Petunias turn brown quickly and need to be physically picked off or the display looks nasty and underdeveloped. It receives sufficient water, is in a full sun location immediately adjacent to traffic lanes. Genetics or environment? I'm theorizing that the blossoms are environmentally sensitive and since there's plenty of exhaust nearby, the stickiness adheres smog and exhaust particulates. The plants look healthy other than that... Anybody else found this to be true?