Our local nurseries only carry the peony roots in the spring, which is unfortunate. I went to all of my nurseries in the fall, and they had nothing. I've never seen Itohs in bags here.
The herbaceous peonies that I get in bags are planted in pots, and I leave them there for 6 months to a year or more, so that I have a little more control of their growing environment. I have a Festiva Maxima, and several peony Vivids that had been in pots, and they were planted in the garden last fall. I'm interested to see how they're going to do this year.
