I have successfully rooted a tree peony when something broke a plant. I just put the broken portion into the soil and left it alone. Probably would be better to put the pruning into moist sand not potting mix. I have not grafted for several years but it is better if the root is the same size as the cutting. I do have a book and a friend has done it where you place buds cut from the stem into sand then use plastic wrap to cover the container until roots appear. If you do either method have patience.
