If you've got window boxes... They just started coming up: my drought resistant wildflower seeds. Planted only five days earlier, they are soon going to burst out of my window boxes, and the best thing is that they will be low maintenance and won't die easily.
Window boxes - mine especially - get very hot in the summer, dry out quickly and easily kill typical window plants, so I turned to the hardiest of the lot: wildflower seeds that thrive on dry land. Sold in many different kinds on Amazon and elsewhere, these seeds are cheap, come up quickly, flower with great color and last you all summer long.
Here's a pic of the kind of thing that you will get