There are pros and cons for either. Since you are apparently in Pennsylvania you might consider joining the MidAtlantic Peony Group and purchase at their sales. Depending on the size of the root that you would plant this fall you might have a bloom next Spring but the plant will be starting to establish itself. If you wait until next spring and purchase a blooming plant after it is finished blooming you could plant then or wait until fall to plant. Any feeder roots will not emerge until the cooler fall weather so although if you are lucky you might have blooms the following spring but again no fully blooming plant for about three years. One thing that you must consider is that Coral Charm can grow from very small root fragments. Removing all fragments is virtually impossible so if you decide to move the plant eventually another will popup where the original was planted.

I think the MidAtlantic group sells plants in conjunction with Swarthmore's fall sale or you can contact Eleanor Tickner directly. She normally has some plants in pots for most of the year. http://midatlanticpeony.org/home.html

Thanks so much maifleur01 ! Great info/tips!