Remember your tree peonies will have stunning flowers for only a few weeks in spring. Those flowers will also crisp off very quickly in full sun, although the plants do need plenty of sun for the rest of the year. So look for nice foliage and think about other flowers to place with the tree peonies as a backdrop during the summer.

You should plant potted peonies now. I'm guessing they haven't flowered yet? Maybe they are too small to flower this year. You don't have to use lobster compost, but tree peonies prefer somewhat alkaline soil and certainly not the very acid soil that is common around Boston. They also prefer good drainage and deep soil where they can establish a very deep root system. I would rather amend native soil to improve drainage and alkalinity, rather than backfilling with something different. Ideally, amend the whole planting bad to have sufficient limestone and organic matter. Don't just throw a bunch of gravel into the planting hole - that's called a french drain and it will fill up with water from the rest of the garden :)

You should plant the graft, if you can see it, around six inches below the level of the soil. Otherwise, just plant the whole thing six inches deeper than the level in the pot. This will reduce the number of herbaceous peony suckers, possibly you'll get none, and will allow the tree peony to grow its own roots eventually. This is another reason to provide deep soil, since you will already have a hole well over a foot deep and the roots haven't even started to grow yet!

I can recommend Rimpo as a dark red variety but there are many others.

My three tree peonies are about one foot tall from the top of the pot. I think I can locate the graft spot. If I were to plant the whole think 6 inched below the top level of the pot, then my plants would look strangely "submerged" in the dirt bed....is this ok? or have I misunderstood you. Thank you for your time. By the way, I acquire my third tree peony yesterday at another nursery...it is a purple flower variety with a long japanese name (I dont have it with me). So I will seek out the red type that you had mentioned. mike