One thing that you can do besides medians and dwarfs that bloom early, is to look for tall bearded iris that are marked as early bloomers. They usually are well on their way by the time the trees leaf out. The later bloomers will bloom if they get enough sun in the winter and early spring to grow well. I have some later blooming iris that need a bit of shade in the afternoon so they don't wilt from the heat. Just don't plant in shade.
