AMES, Iowa -- Peonies can thrive up to 100 years if maintained properly. Horticulturists with Iowa State University Extension and Outreach answer questions about late season peony care, specifically when to divide the plant and cut back foliage. To have additional plant and garden questions answered, contact the ISU Hortline at 515-294-3108 or firstname.lastname@example.org.
My peonies appear to be covered with a white, powdery substance. What is it?
The white, powdery material on the peony foliage is powdery mildew. Powdery mildew is a fungal disease. Powdery mildew occurs on a large number of plants (peonies, lilacs, viburnums, roses, garden phlox, bee balm, turfgrass and many others). Fortunately, powdery mildew seldom causes serious harm to plants. The damage is mainly aesthetic.
Powdery mildew tends to be more common on peonies growing in partial shade. Moving peonies growing in partial shade to full sun often helps reduce the incidence of powdery mildew.
When is the best time to transplant peonies?
Mid- to late September is the best time to transplant 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.
If desired, large peony clumps can be divided at this time. Using a sharp knife, divide the clump into sections. Each division should have three to five buds and a good root system.
When replanting, dig a hole large enough to accommodate the entire root system of the peony. Position the plant/division in the hole so the buds are 1 to 2 inches below the soil surface. Fill the hole with soil and water thoroughly.
When can I cut back peony foliage?
Cut back peony foliage after it has been destroyed by a hard freeze. In Iowa, 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 fall.
Photo: Peony living and the dead. Flowers bloomed and wilted by ivan4es/stock.adobe.com