I also want to add that buying potted roots will eventually lead you to appreciating the peonies more and save in the process as some of them can be bought for 10 dollars or cheaper and can be bought on a whim.
But some of us get hooked and want different/rare/more beautiful or fancy varieties and start on the path of ordering rare or more eye-pleasing bare roots from reputable growers. Still I could not resist when I saw potted Madame Calot for 1 dollar on sale and after 2 years of growing there is no bloom. I really hope it could be the right ID or at least the one I would like.
