Yes you can. Just cut the root runner off near the pot and replant the offshoot. I would divide the main plant as well. It will grow and bloom even better if it's not pot-bound.

Thanks cherokee joeshoeboot.

I can't believe how fast these irises grow!
I will probably take out the potbound one and replant all those root runners. With the arthritis in my hands, that would be easier for me that struggling with sawing the pot and over-grown plant apart. One of them even ran out of the pot and rooted in my waterlily container.
Its hard keeping some of these guys in line. :)
Thanks for your help!

My Irises came in small pots that I put into the pond several years ago. They busted out of the pots after about 2 years and got quite dense and large.

What I have been doing for the last 4 years, is to wait until fall when its time to cut them back. After cutting them down I rip about half of them out and discard them. Its not easy because the roots get extensive and entangled in rocks and stones but when spring comes they are ready to grow again. Some cutting and prying with a small trowel is usually required. Now they are rooted in the pond gravel. I think I got all the pot pieces out ;-)

I just brought the pots from my old pond down to KY to put into a temp water garden and couldn't believe what I had. My ex was supposed to be taking care of them (LMAO) but evidently did nothing. Every single pot had 3 or 4 different plants in them. There are so many iris that I don't know what to do with them all and since I had several colors I don't want to throw any away until they bloom. Also have arrowhead, dwarf cattails and a couple of other things.

I made the mistake of trusting my memory as to which pot had which color iris in it. Bad move! haha So I need to wait until they bloom too........IF they bloom, since they are sooooo pot bound. I think its the yellow flag that seems to be the most aggressive..........but it might be all of them.
I put a few starts in my small lotus bog. I hope it doesn't take over the lotus bog. It would be a pretty good duel though......they're both pretty strong.......