Peonies grow successfully for many years and spread rapidly. Due to their hardiness and aggressive nature it often becomes necessary to divide the plants when they outgrow their site and transplant them to new locations. When the peony's foliage turns yellow, the plant is beginning to go into a dormant stage. It has successfully accumulated enough nutrients to see it through the winter. This is the time to dig up the plant's tuberous root system and replant. Dormancy usually begins in September.
Dig 10 inches out from the plant's stems. Use a hand trowel to gently lift the soil away. Work the soil in a circle around the plant. Dig approximately 4 inches deep.
Angle the hand trowel inward once a the plant is dug out in a circle. Work the hand trowel under the peony. Do not pry the plant because the roots will be damaged. Slowly work the hand trowel under the peony plant so that the plant and its root system roll free from the dirt and the roots are not damaged.
Shake the dirt away from the peony plant's root system. Use a gentle water spray from the hose to sufficiently wash away the dirt so the plant's root system is clearly visible.
Divide the peony plant's root system to replant the peony in a new location. The peony plant does not do well if replanted as a large clump. It does better when the roots are divided and replanted in a new location.
Cut downward with the hand trowel or a sharp knife into the peony plant and the root ball. Divide the large roots so each root has at least three buds with feeder roots attached. New peony plants can often be started from smaller pieces of root, but it is often more difficult then the larger roots which have stored sufficient nutrients for the coming winter.
Place the divided roots into moist peat moss for a few days. This allows the division cuts to heal over before planting.
Plant the peony plant in a location that offers full sunlight. Rich soil that is well-draining is ideal. Place the roots of the peony plant 1 to 2 inches below the soil's surface. Space the peony plants 4 feet apart. Firm the soil around the roots. Water thoroughly.
Apply 3 to 4 inches of peat moss, straw or bark chips over the replanted peony roots. The mulch will help protect the roots from the winter weather.