IMHO, no matter WHERE the iris is grown, or what conditions it's grown IN, all you have to do is get it through the first year....after that point, the rhizomes that are there are "daughters" grown in YOUR zone
. That said.....some varieties do well....everywhere, .....and some varieties don't. There are some very beautiful irises that are known for being "hard to grow",especially in colder areas, but by utilizing "micro climates" in your yard, you usually CAN get them to grow / bloom, even if they never really become "thrivers"