Peonies can be left undisturbed in the garden for many years. Occasionally, however, it becomes necessary to move established 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 established peonies. Begin by cutting 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. Promptly replant the peonies 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. 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. Smaller divisions will require several years to develop into attractive plants.
Peonies perform best in full sun and well-drained soils. When selecting a planting site, choose a location that receives at least 6 to 8 hours of sunlight each day. Avoid shady areas near large trees and shrubs. Poorly drained soils can often be improved by working in large amounts of compost, peat moss, or leaf mold.
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 late fall (mid-November to early December), apply a 4 to 6 inch layer of mulch over the newly planted peonies. Excellent mulching materials include weed-free straw and pine needles. Mulching prevents repeated freezing and thawing of the soil during the winter months that could heave the plants out of the ground. Remove the mulch in early spring before growth begins.
Transplanted peonies usually don't bloom well the first spring. In fact, it's advisable to remove any flower buds that develop the first spring to promote root and foliar growth. The transplanted peonies should bloom well by the third or fourth year.