Kent, You say you can do this anytime?! (Spring, Summer or Fall)
Yes, you can do it any time. I like to thin the ones that are crowding their neighbors in the early spring because that is when it's easiest to see what's going on. You have to understand the growth cycle of the plant, though. Thinning in the early spring likely costs some bloom stalks, but usually the ones that are crowding their neighbors will produce plenty anyway.
As I said in the article, we don't have a lot of problems with rot here, but if you do, you'll want to be careful about when you thin. Generally, bearded iris are most vulnerable to rot under hot and humid conditions with saturated soils.
