I have a wave petunia in a hanging basket, and several other plants in window boxes, and some of the leaves are turning brown on the edges... any ideas why, and how I can stop this? I've fertilized a couple of times, keeping the soil moist, but not soaking, and not drying out.

Were they fine before fertilizing? It's easy to over do it or provide too much of some nutrients and not others. Also see What Causes Brown Edges On Leaves Of Plant, Are Your Plant Leaves Turning Brown?, and Plant Doctors.