When tree peonies are not planted deep enough, the herbaceous root stock will sprout and take over the plant killing the tree portion. This is not a reverting plant, but an incorrectly planted tree peony. It is best to wait until fall when the plant is dormant to dig it up and replant deeper. Until then, pinch off any herbaceous growth and do not let it grow. When I first started growing tree peonies, I had one plant (my first) that persistently put up herbaceous roots. Eventually, I got so frustrated I dug it up (in July) and used a saw to cut off the majority of the herbaceous rootstock. I replanted the remains deeper and I planted the herbaceous rootstock I cut off (if it has eyes, it will grow). Both are happy individual plants now. If the tree peony portion of your plant has any roots at all replant. You may lose what is above ground now, but hopefully the tree peony roots will put up new growth the next year. I now have 12 tree peonies that are the crown jewels of my garden. But they are fickle and temperamental plants that don't like to be messed with once in the ground. The best advice on growing tree peonies is you have to have patience with them, but eventually the patience will be rewarded. Good luck.
