I would not plant irises in that dirt again. The rot is living there..... and winning. I guess you could bake it or sterilize it by putting it in a tub with the bleach/water mixture buy why try if you have other growing space. When I have rot and I had a bit last summer, I dig, perform surgery, soak and sometimes use a soft brush to make sure rhizome is clean, dry and let the rhizome sit out to callous over the new cuts, dust with comet and plant in a fresh spot. Then I go to the place where the iris was infected and dig the dirt out and throw it in a ditch or use it to fill a dip in the driveway.
