Grafting to an herbaceous root is the most common practice for grafting tree peonies. There are a few that graft onto tree peony roots but I do not know of anyone that practices this nor have I seen a tree to tree graft.
Even the more expensive ones normally start out as a graft.
As a side note somewhere in my house is a older garden book that discribes some earlier practices. Grafts at one time were done in April, probably with new shoots. Other than stating the graft was done the ususal way no additional information. Also in the book was mention of cutting buds of the tp in June, laying on moist sand, putting in a dark place until roots develop on the buds. I have talked to one person that has attempted the latter practice with some success but the establishment of the roots took too long. These are things I have on my back burner to try. One of these days???? Anyone like to try. What I wrote above is almost all the information in the article.
