There’s a formula for a classic window-box look: You need a thriller, a filler and a spiller. For example, you could plant three or four tall, bold geraniums amid a tranquil bed of white impatiens, with ivy vines flowing down the front. But if you’re an experienced window-box creator, you might be ready for a challenge. How about using herbs, nasturtiums and scallions to create a window box full of edibles, or a window box themed on succulents or carnivorous plants? And remember, window boxes aren’t just for window sills. They can sit on porches, patios or front steps too, or add color to the side of a drab shed.