There have been discussions about raising Dutch iris and where they could be reliably grown. Here are a few I had extra from a plot which was planted about 3 years ago. These were planted in the sunny side of a drip line of a maple tree. They have bloomed every year, surviving nearly zero degree winters and very hot summers. These are still green after several nights of heavy frosts or freezing temps. I am on the border between zones 5b and 6a. The mulch is to help keep the weeds down and not for insulation.
That's what happend here too, Paul. I thought it was because the winter was so mild, but they continued growing when spring came and then bloomed. This fall they came up again, and are about 5 or 6 inches tall.