You can get a better deal at treepeony.com or charmarron gardens. Both have the same plants at a much cheaper price. Healthy roots.

I also thought of putting a tree peony in a pot, Alice Harding is a very short tree with downward facing flowers. Asked Carol Adelman via email if that was a good idea and she was fairly negative. Said the constant freezing and thawing that takes place when in a pot will kill the tree. If you can find a place to put the pot where it wouldn't go through that cycle you'd have a better shot of it surviving.

When you get your tree peonies make sure you plant them several inches deeper than the herbaceous peonies so the nurse roots don't start putting up sprouts!

If you can sink the pot under the soil in winter, there may be no problem. Or if you can put the pot in not so cold but not too warm place such as garage. It will be better to use breathable growing bags instead of pots.