Welcome to the iris forums, Marci!
From what I'm hearing, it is possible you're either overwatering, overfertilizing or snippets of both for your irises. I second Evelyn with the question of how much you're watering them.
Depending on how much, some of your irises may have been poised to rot, and even some succumb to it. Usually, an iris of the bearded kind....are they the "bearded iris?" that look like this?
Notice the fuzzy looking things on the petals that fall(That's how you know it is a bearded iris!).
If not, you might have other beardless varieties, particularly some that need a lot more water than you'd guess, but it sounds like you have bearded irises. If ya do, bearded irises usually only need "thick" watering for a few weeks, or until they've set in. Then they're really drought tolerant and don't need water so much as even every two weeks. I say, water them when it hasn't rained in...a week at least, and I've known the optimal fertilizing time is six weeks before the bloom (roughly April-May for blooms, so March at the latest), and right after the blooming period so that the rhizome (the fancy term for a long rhizome) can set in place increases and further blooms.
I hope this helps you - I am sure there are plenty more experienced iris veterans that can help too. Hey, if you stick around, pretty soon you might be hoarding irises because you've gotten addicted to them....
