Guess we'll have to wait another year or two for the huge, mature clump but pictures of the blooms would be wonderful, LG! Did you plant the divisions near each other or spread them out among other flowers? I've accidentally created a huge clump of a single variety before, a coral with adventitious roots, ended up with 3 large shrubs butted up to each other, it's very pretty. Mixed in with other flowers is prettier for longer, though!
I think most herbaceous and Itoh peonies benefit from being split. After several years they just don't increase as much, do they?
