They are grafted onto herbaceous tree peonies. The grafting point is supposed to be 4-5 inches below the soil surface.
This is the first time I have planted tree peonies, and I don't know for sure where the grafting point is!
Here is a picture of one of the tree peonies:
I have placed an arrow where I have guessed the grafting point is. Could someone with some experience let me know if the arrow should be higher or lower? I'd be very grateful, these are quality three year old plants from goldenport.com and were very expensive!