@DogsNDaylilies, You can plant the peonies until the ground is frozen. Planting them in Sept. will allow them more time to grow feeder roots so that they have more probability of blooming next spring. That was why I wanted to get them out early esp. for zone 6 or lower. Fernleafs or fernleaf hybrids or early blooming varieties will benefit from planting early. Not so much with doubles or later blooming peonies.
At this time, I am all out of the peonies for sale. If I have peonies for sale next fall, I will definitely notify you. However, they will not be the same varieties that are offered this year.
