I am assuming you have german iris?
German irises can be transplanted easily, they claim the best time to dig/divide/replant irises of this type is in July when the plant goes dormant, but I do it anytime from spring to late fall. The newer tubers will bloom the first year, the older don't bloom - their job is to make new babies. If you want blooms, take some from the outside ring of your clump, and also take one or two from the interior so that you've got some new babies next year.
I dig mine, then cut off any part that has been torn - I use a small knife and wipe the knife after each cut with some sort of "something" - hydrogen peroxide on a paper towel, an antibacterial wipe, a bit of diluted clorox - this helps to prevent disease. I throw away any tubers that have a lot of holes (borers) or have mushy soft spots.

Sounds like a chore, but it goes very quickly and gives great, healthy clumps of iris!

girlgroupgirl