Peonies can thrive for up to 100 years if maintained properly. Horticulturists with Iowa State University Extension and Outreach answer questions about peony care, specifically how and when to divide the plant. To have additional plant and garden questions answered, contact the ISU Hortline at 515-294-3108 or firstname.lastname@example.org.
Peonies do not need to be divided on a regular bases. They can be left undisturbed in the garden for 50 or more years. Large peonies can be divided if additional plants are desired.
September is the best time to divide peonies. By September, peony plants have been able to store adequate food reserves in their roots for the following year. The replanted divisions have several weeks to get reestablished at their new sites before the onset of winter.
Begin by cutting the peony stems near ground level. Carefully dig up the plants and wash or gently shake off the soil. Using a sharp knife, divide the clump into sections. Each section should have three to five buds (eyes) and a good root system. Divisions with fewer than three buds take longer to flower.
When planting, dig a hole large enough to accommodate the root system of the peony. Position the peony in the hole so the buds are 1 to 2 inches below the surface. Fill the hole with soil and firm the soil around the plant as the hole is filled. Once the hole is filled, water thoroughly. Space the peony plants 3 to 4 feet apart.
Mulch the newly planted peonies with several inches of straw or pine needles in late fall. Mulching prevents repeated freezing and thawing of the soil that may heave and damage young plants. Remove the mulch as growth resumes in the spring.
Cut back peony foliage after it has been destroyed by a hard freeze. In Iowa, late October or early November is generally a good time to cut back peonies. Cut off the stems at ground level. If the peonies experienced foliar disease problems, remove the plant debris from the area and destroy it.
Plants cut back in August or early September may have fewer blooms than those cut back in late fall.