Other than flowering plants, are there any plants with colorful leaves that grow well in your area? Then you don't have to worry about the plant blooming, just keeping it alive is all that's necessary. Although, if you used plastic or silk flowers, you'd not even have to do that. Dunno as if they'd look tacky or not, though. I've had a window flower box full of silk flowers before, it looked festive and was much easier to care for than a real one in that windy location would have been.
![](http://i649.photobucket.com/albums/uu219/hotzcatz/100_4142_zpsbf7f72b5.jpg)