Is it possible mulch decomposed as well as winter rains pounding them down or washing soil over them? Perhaps the soil underneath them was more tilled than surrounding soil?

As far as I know iris do not have the contratile roots lilies have.

If you have well draining soil I would not disturb now except to try to expose the tops of the rhizomes. The very best time to divide is immediately after bloom. That practice gives the rhizomes the longest time to produce babies and inner flower bud creation.

Bloom production lessening is a sign for division. Most beardeds can easily go 3 years. Vigor varies. Soil nutrition varies. So no hard and fast rules.

Many people experience less bloom after dividing. And most people wait for a couple of months after bloom to divide (including me). When the iris are looking tired but actually are forming inner flower buds. So I am revising my schedule this year.

BlueJ sent wonderful rhizomes. Almost 100% bloom the first year! I've never seen the ones you have ~ pictures when they bloom?

PS: when using the term dividing it means lifting the whole clump and breaking apart rhizomes from one another. Less disruptive is digging away a portion. Not sure what term would be used for that.

I can tell you that definitely YES some of the irises dig themselves down deeper. I live on a sandy loam hill and many of them in my garden have done so.

Last fall, I dug around them, and lifted ([pulled them upwards gently) and then put dirt under the rhizome. I did NOT pull them completely out of the soil. Don't know what effect this has had yet, as none have begin to bloom....well I do have two blooms on the 'funeral whites'.

You know, I have a theory about this. I plant my rhizomes very high, and on a little mound of dirt to boot, but by spring they seem to have buried themselves. I think the original rhizome is still in place, but all of the new fans come up from below the soil surface, and their rhizomes are below grade.
Renee

I would brush the soil from the top of the rhizome. And leave the roots just as they are. If they are really significantly below grade, maybe lift the entire clump, soil, roots and all, and reposition it on on bit of soil added to the spot to raise the grade.

I have the same theory as Renee. most of the original rhizomes are there but newer offshoots are coming from what appears to be underneath.

I have to go pull my garden map now to see which 2 I lost that didn't take this winter. Sigh :(

I have to say, all of them are doing well now. I just took off all the mulch from around them, and left them as they are. They are all growing new leaves. Now, we'll have to see if they flower!

My rhizomes tend to come a little farther up as they multiply. My own suspicion is that they adjust their own level to the climate they are growing in: colder winters, deeper rhizomes; warmer winters, shallower rhizomes. My hard clay soil may also be a factor, though I try to condition it.