Peonies are perennial flowers that bloom and thrive for many years. If they begin to bloom less profusely as time goes by, chances are the peonies have become overcrowded and it is time to thin them. Digging up and dividing peonies also helps you expand your flower bed. The new root sections can be replanted in other areas of your garden, where they quickly grow into new plants. Thin peonies in early autumn so they have a chance to set new roots before winter.
Cut the peony plant down to 4 inches high using clean, sharp shears. Dispose of the removed plant matter as leaving it in the bed may lead to the spread of disease.
Dig around each plant, then slide the trowel under the roots. Lift them from the soil and brush off any excess dirt from the roots.
Check the roots for signs of rot or disease. Look for soft spots, lesions and damaged areas. Cut off any that are found, using a sharp knife, and discard them.
Cut apart the root clumps with your knife, leaving three to five growing eyes per section. Growing eyes look similar to the eyes found on potatoes but they are red.
Lay a 3-inch layer of mature compost on top of the garden bed. Till it in to an 18-inch depth with a hoe or power tiller.
Plant each root section with the growing eyes facing up and approximately 2 inches beneath the soil surface. Space plants 24 to 36 inches apart.
Water the bed until it is evenly moist but not soggy. Lay a 3-inch layer of straw mulch over the bed to protect the plants over winter.