Maryl, I an in zone 7a, verging very closely on 6b, and my Red Velvet Elvis LA iris does great. I think moisture is more important to them than temperature. I have it planted in an area where the neighbor's sump pump annoyingly drains onto my property. But Elvis loves it and over years has formed a large, vividly blooming clump at least three feet wide. LAs can survive very much further north than this if given the moisture they like. I have Dorthea Kay Williamson, too, and it grows like a weed.
