Many peonies are hardy to United States Department of Agriculture Plant Hardiness Zone 2, making them a reliable garden plant in Minnesota where winter freezes can begin as early as Sept. 1. Spring comes late. Minnesota’s last hard freeze occurs from May 1 to June 1.
Peonies bloom in early spring. They often begin herbaceous growth before late snows have completely melted. They need a cold dormant period to bloom well. In areas of Minnesota where winter temperatures drop below minus 20 degrees, plants require mulching.
Late spring freezes mean that dividing Minnesota peonies in spring, although possible, will result in the loss of at least one season of bloom. It interrupts the plant’s growth cycle by forcing it to put all of its energy into growing roots that support blooms rather than producing the blooms.
Peonies survive spring planting in Minnesota and container-grown plants can be planted any time. Fall planting of peonies allows root growth before cold dormancy rather than after, so August through mid-September is the optimum time for dividing peonies in Minnesota.