Before I planted peonies only in spring. They were potted peonies in a local nursery where they received roots in March and sold growing plants in May. The peonies have been very slow in developing but it could be due to the quality of roots. Once I ordered roots from ponynursery in spring and the roots were bad. Eventually half of the peonies did not survive. And I heard they could be mis-ID so I don't know what kind of blooms I will get
I learned from a lecture on growing peonies here that if you plant in spring you don't count the current year as a growing year for the peonies, the first year will be the next one.