Only because they have Never bloomed do I recommend doing this as soon as your soil is warm enough to work. Normally it would be done after spring bloom.

As soon as their new sunny bed is ready, dig them up; shake off excess dirt; toss all dead-dried out-shriveled old rhizomes; break off the fat firm rhizomes having a fan of leaves; cut roots and leaves to 6 inches; let them sit overnight in a dry shaded place; plant with tops of rhizome exposed.

One method of planting is to use 3 rhizomes sticking out from a center point (leaf end out 'cause that's the direction the rhizome will grow). 3 feet away repeat with another 3 rhizomes.

If you're worried about where to break them, relax. I have seen iris grow from a rhizome 1 1/2 inches long or shorter. Since that is their food storage tank I like them 4-5 inches long.

A google search on bearded iris culture will hopefully turn up some sites with drawings.

Could I add a bit to that? When you plant them, leave just a bit of the rhizome above the ground & don't mulch them. I'm with iris gal, I'd go ahead & move them as soon as their new bed is ready since they aren't blooming anyway. Normal time is a few weeks after they bloom. Iris need to be divided every 3 years or so, although mine go longer than that. I'm sure, even after you have tossed out all the dead rhizomes, you will have many, many more iris than you expect :)

If they are under a tree, they are probably not getting enough sun. Iris are plants that like serious sun.

To expand on Mad gallica's post...Irises need a good 6 hours of direct sun a day to bloom well. I would also throw some super phosphate or bone meal in the bed and mix it in well. Follow these two things and you will have Irises everyone will be envious over. Good Luck!

I wanna see pictures when these bloom!