Growing Peonies
- Hope Weber, Horticulture and Crop Science, OSU Extension Serv. (HYG-1241-94)

Peonies are perennial favorites in the Spring flower garden. Few herbaceous plants can rival them for floral display and foliage. Their exquisite, large blossoms, often fragrant, make excellent cut flowers and the foliage provides a background for annuals or other perennials.

Two types of peonies are generally grown in the home landscape, Paeonia hybrids or garden peony and Paeonia suffruticosa or tree peony.

The following information pertains to Paeonia hybrids. Peonies are classified according to flower form. All peonies have five or more large outer petals called guard petals and a center of stamens or modified stamens. Single forms have centers of pollen-bearing stamens. Centers of semi-double forms consist of broad petals intermingled with pollen-bearing stamens. Double types have dense centers of only broad petals (transformed stamens). The anemone form, often included in the semi-double category, may have more than one row of guard petals encircling a center of thin, petal-like structures. Japanese types are similar to anemones but have staminodes (stamens that do not produce pollen) in their centers. Flowering usually lasts one week in late spring to early summer. By selecting and planting early, mid- and late-season bloomers, flowering may be extended for six weeks. Flower color may be any except blue.

Peonies grow from two to four feet in height. Support is often required for tall, double hybrids. Peonies thrive in sunny locations and well-drained soils, tolerating a wide range of soil types. Best growth is in soil with a pH range of 6.5 to 7.5, deep and rich in organic matter. They are hardy from zone 8 to zone 2 (central Ohio is zone 5) with some exceptions. In cold climates, those with an average minimum temperature below -20 degrees F, winter mulching is necessary if there is little or no snow cover. Because winter chilling is required for dormancy, peonies do not perform well in subtropical areas. Planting, transplanting and dividing peonies are best done in early fall but may be done in spring as soon as soils are workable. Each plant requires an area about three feet in diameter. Dig a generous hole, large enough to accommodate the roots, and incorporate aged organic matter in the bottom. Place the peony in the prepared hole so that the eyes (small, red-colored buds) are one to two inches below the soil's surface. Backfill and water well.

Peonies may be left undisturbed for many years. A decline in flower production usually indicates overcrowding and the need for division. Carefully lift the clump and wash away the soil to expose the eyes. Using a clean, sharp tool, divide the clump into sections, each with three to five eyes and good roots. Replant immediately.

Pests and Problems

Peonies have few pests or problems. The most frequently occurring pests are botrytis blight and leaf blotch, both fungal diseases. Especially prevalent during wet springs, botrytis affects leaves, stems and flowers. Spots appear on leaves, stems soften and decay, and flowers either rot or buds blacken and fail to open. Prompt removal of infected material and a thorough fall cleanup are essential for control. In spring when shoots emerge, use a fungicide labeled for botrytis according to package instructions. Leaf blotch develops during warm, moist weather. Glossy, dark purple spots form on the upper surfaces of leaves. Again, removal of infected leaves and good fall cleanup are necessary for control. At first signs of infection, apply a properly labeled fungicide. Avoid overhead irrigation.

Other fungal diseases include Phytophthora blight and Verticillium wilt. These are soil borne fungi with no cure other than destroying infected plants. Do not replant in diseased soil.

The only insect pests of any consequence on peonies are scales. Scales are seen on stalks and leaf bases in late summer and over winter on the below ground portion of stalks. For control, remove plant material in fall then apply a properly labeled insecticide in late May and mid-June the following year. The presence of ants on peony blossoms is neither beneficial nor harmful to the plant. Ants are simply attracted to the sugary liquid secreted by flower buds.

A common problem of peonies is the failure to bloom. It may be the result of: