I know that the growing zones are the only info we have about our areas, but that only lets us know the regions with the same lowest average temperatures, not the length of our growing season. More important than the coldest temp when dealing with re-bloomers is the length of the growing season, I believe. You can help them have a longer growing season by planting them in a micro climate, like on the South side of a building, or by covering them to protect them from an early frost in the fall. Also there are special needs that help re-bloomers to re-bloom, namely, you don't want them to go into a long summer dormant stage, so to prevent that, they need more water then the typical iris, and it also helps if you fertilize after the spring bloom. Because of these special needs, many people who have re-bloomers tend to plant them in a common area so that they can more easily give them what they need. George Bacon from Breezeway Iris Gardens has had some very significant success with getting re-bloomers to perform in his Zone 5 garden. He also has a large collection of them for sale. Good Luck!
