If the planters are large enough for something like Cuphea Vermillionaire, that's a sure magnet for hummingbirds. There's a variety I just saw this year for the first time that will trail a bit more, Cuphea Honeybells that would probably be great in planters on a railing. I've had such great success with Vermillionaire that I decided to stick with it, but either should be great. They don't get more than 14" or so for me in containers.
Others I plant in containers are salvias and hummingbird mints. Skyscraper Salvias do well and don't get too tall. Ones I've started from seed that do well are Arizona Sunset Hummingbird Mints and Summer Jewel Red Salvias.
With any luck you can still find some live plants, around me all the good stuff is literally gone by mid-June or earlier. The cuphea never fails to bring hummers. If you've never seen them in the garden before and can't get cuphea, you probably have time to start some seeds so you'll have flowers for the fall migration. They're said to remember where they found flowers and return in later migrations, so if you get them going early enough next spring, you should get them.
It was sparse going at first, but after making sure their favorites are always available, I now see them daily on the planters every year.
