July if possible. You can plant later but that amount of time before winter gives the plants time to really get rooted. I assume he is talking bearded irises. Breadless late aug. or perhaps early Sept.
I live in the next county east of south bend. I plant my irises in later part of july/first of aug. Or from now till mid aug. They do just fine for me. Just tell your friend to water them in good before it gets cold.
Name: Leon Indiana If it ain't broke don't fix it!
I'm right down the road from South Bend in Miami County off U.S. 31. I'm in the midst this week of replanting, thinning, and trying to figure out what to do with so many rhizomes. From now to the end of July works for me.