Peonies can be left undisturbed in the garden for many years. Occasionally, however, it becomes necessary to move plants. Peonies shaded by large trees or shrubs should be moved to a sunny site to improve flowering. The redesign of a perennial bed or border may require moving the peonies. Large, vigorous plants can be dug and divided for propagation purposes.
September is the best time to transplant peonies. Begin by cutting off the peony stems near ground level. Then carefully dig around and under each plant. Try to retain as much of the root system as possible.
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. Using a sharp knife, divide the clump into sections. Each division should have at least 3 to 5 buds (eyes) and a good root system. Divisions with fewer than 3 buds will likely require several years to produce a good flower display.
Peonies perform best in full sun and well-drained soils. When selecting a planting site, choose a location that receives at least 6 hours of direct sun each day. Avoid shady areas near large trees and shrubs. Poorly drained soils can often be improved by working in large amounts of compost or sphagnum peat moss.
When planting a peony, dig a hole large enough to comfortably accommodate its entire root system. Position the peony plant in the hole so the buds are 1 to 2 inches below the soil surface. (Peonies often fail to bloom satisfactorily if the buds are more than 2 inches deep.) Fill the hole with soil, firming the soil around the plant as you backfill. Then water thoroughly. Space peonies 3 to 4 feet apart.
In fall (mid- to late November), apply a 4- to 6-inch-layer of mulch over the newly planted peonies. Excellent mulching materials include clean, weed-free straw and pine needles. Mulching prevents repeated freezing and thawing of the soil during the winter months that could heave plants out of the ground. Remove the mulch in early spring before growth begins.