I'll hazard a guess- zones 3-7 in the South, and 3-10 in the west? I think tall bearded irises have a hard time in the very hot and humid South, but not in the dry heat of the west. That is the problem with using the USDA zone system. It's based on frost dates, and does not take heat and humidity into account. In the west, we are lucky to have the Sunset zones, which are much more useful.
Renee

thank you

rdeal

Well I'm curious where you saw the hardiness zones listed like that. In looking at the site (if it was on line) might give an additional clue.

Sue