In my experience, irises are among easiest flowers to transplant.
One spring many years ago, an older friend of mine dug up an iris bed at her home. They were bearded irises -- a lovely shade of lilac purple -- and she moved some of them to a different location. The irises had already started to grow and were about four inches high. She didn't know what to do with remaining irises, so she put them in a box, intending to give them away.
As it turned out, irises remained in box for more than two weeks. By now, she didn't feel she could give them away because she didn't think they would grow. I offered to take irises and plant them, just to see what would happen.
The irises were not one bit bothered about being in a box for more than two weeks with no water and no dirt around their roots. I planted them, they started growing, and they're still going strong more than 25 years later.
In past two decades, I have thinned out irises and planted them in other locations. I have also found irises growing by old homesteads where no buildings remain (I live in rural Wisconsin) and have dug them up and transplanted them in my yard. Each year in early June, irises bloom in a variety of colors: white, blue, yellow and purple.
Here's how to transplant irises:
1. Prepare new flower bed where you intend to plant irises.
2. Use a shovel to dig up roots that you want to transplant. Irises have very tough root systems. If irises are exceptionally thick, a trowel probably won't do trick. Stick shovel into dirt among irises and start digging. And don't worry about cutting roots with shovel. You won't be able to avoid it. Irises spread by their roots, so many of plants will be connected. Even a short section of root stands an excellent chance of transplanting.