Liz, Dutch Iris do the same thing here. They typically bloom nicely the first spring after planting, then either try to grow in fall or winter or don't return at all. I think they are only marginally hardy in this zone.
Have any of you tried the wintersowing method for iris seeds? I've had great luck using that method for anything that requires cold stratification (using gallon milk jugs). If I ever get my act together and make some crosses, this is how I plan to start them.
