They should be fine in the winter, just leave them and don't disturb them because they go through a cycle. I almost lost my best one when I dug them so I could pot some for friends, theirs thrived and mine barely grew after that, it took a couple years to establish another clump.
A lot of times when they talk about summer/winter, it refers to ponds where you would remove them from the water in winter.
They should be planted a little below the surface, not as high as tall beardeds. Maybe mulch them in winter or fall because Japanese Iris grow upward and out of the soil.
I've read that JI's contaminate their own soil, but this has to do with pot culture mostly.

Randy; Thank you so much for your response. I will do just as you suggest.