I just transplanted some this spring that had come up on my path. They were already budding and I took a generous amount of dirt with them. Every one survived and they are blooming now like nothing ever happened to them.

Moving them in early spring or after they go dormant (assuming you know where they are) is preferable, but they can be moved now if you are extra careful and get a large rootball. Be prepared to dig deep and wide! The rhizomes are often much deeper than you might think and won't be directly under the foliage (they will be off to one side). It's definitely best if you can keep from breaking or cracking the rhizome.

I agree on digging them up very carefully and deeply and getting a lot of dirt with them and make sure you get all of the root. I had very good success by transplanting them into a hole lined with lots of leaf mold (i.e., shredded leaves mixed with dirt.) Keep well watered the first season.