I mulch my iris garden also. I have found that if I keep the mulch around the rhizomes, instead of on top of them, it cuts down tremendously on the weeding and does not increase the rot problem. I have an (even) older friend who has gone to raised beds to keep his iris. Just getting the beds up a short distance from ground level cuts way back on the weeds. And the higher the bed are raised the less bending over is involved.
Good Luck in whatever you do!
