AMES, Iowa – Peonies are a beautiful part of any landscape, and they thrive in Iowa. However, they do require some special care and conditions, and can develop problems which must be addressed. Fall is prime time for transplant and division of peonies.
ISU Extension and Outreach horticulturists can help answer questions regarding peonies and helping them reach full potential.
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 plants growing in partial shade. Moving peonies growing in partial shade to a sunny location often helps reduce the incidence of powdery mildew.
When is the best time to transplant peonies?
Peonies can be left undisturbed in the garden for many years. However, they can be successfully transplanted if redesigning a flower bed or wishing to move them to a sunnier location.
Mid-September to early October is an excellent time to transplant peonies. Begin by cutting off 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.
When replanting, dig a hole large enough to accommodate the entire root system of the peony. Position the plant in the hole so the buds are one to two inches below the soil surface. Fill the hole with soil and water thoroughly. Peonies perform best in well-drained soils in full sun.
What is the proper way to divide peonies?
Peonies are propagated by division. Mid-September to early October is the best time to dig and divide peonies. Begin by cutting off the peony stems near ground level. Then carefully dig up each plant and 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 three to five buds (eyes) and a good root system. Divisions with fewer than three buds will likely require several years to produce a good flower display.
When planting a peony, dig a hole large enough to comfortably accommodate the plant’s entire root system. Position the peony in the hole so the buds are one to two inches below the soil surface. Fill the hole with soil, firming the soil around the plant as you backfill. Then water thoroughly. Space peonies three to four feet apart.
When should I cut back peony foliage?
Peony foliage should not be cut back until it has been destroyed by a hard freeze in fall. The foliage manufactures food for the plant. Some of the food is stored in the plant’s root system. The more food the peony plant can store in its roots, the better the flower display next spring. Cut off the peony stems at ground level in late October or early November. Remove the peony foliage from the garden and destroy it. The removal and destruction of the peony debris helps to control leaf blotch and other fungal diseases.