Peonies can be left undisturbed for many years. Sometimes, however, it becomes necessary to move established plants. Peonies shaded by large trees or shrubs bloom poorly and should be moved to a sunny site. Large, old plants may become overcrowded and flower poorly. Large, old plants should be dug, divided, and transplanted to improve performance. The best time to move and divide peonies is September.
Moving established plants is a simple procedure. Cut the peony stems near ground level in September. Then carefully dig around and under each plant. Try to retain as much of the root system as possible. Promptly plant the peony in a sunny, well-drained site.
Division of large peony clumps requires a few additional steps. After digging up the plant, gently shake the clump to remove loose soil from the root system. Divide the clump into sections, making sure each division has at least 3 to 5 eyes (buds) and a good portion of the root system.
Peonies grow best in full sun and well-drained soils. Dig a hole large enough for the entire root system. Place the peony plant in the hole so the eyes are 1 to 2 inches below the soil surface. (Peonies planted deeper than 2 inches often fail to bloom satisfactorily.) Fill the hole with soil, firming the soil as you backfill, then water thoroughly. Space plants about 3 to 4 feet apart. Apply a 2 to 4 inch layer of mulch in late fall. Straw is an excellent mulch. Mulching will prevent repeated freezing and thawing of the soil that could damage the plants. Remove the mulch in early spring before growth begins. Transplanted peonies will not bloom well the first spring. They should be back to full flower production by the third or fourth year.
This article originally appeared in the August 23, 1996 issue, p. 145.