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Missouri Environment & Garden


David Trinklein
University of Missouri
Plant Science & Technology
(573) 882-9631

Plant Peonies in September

David Trinklein
University of Missouri
(573) 882-9631

Published: September 8, 2017

pink peonies in vase

Peony is one of America's most popular garden perennials. Used both as an attractive garden plant as well as a valuable cut flower, it's spectacular, often fragrant, blooms are a marvel to behold. Its ease-of-care and longevity make it one of our best perennial flowering plants. September is an ideal month for planting or transplanting this regal ornamental.

A member of the plant family Paeoniaceae, peony is named after Paeon. The latter, according to Greek mythology, was the student of Asclepius, god of medicine and healing. Supposedly, Asclepius because jealous of Paeon and threatened to kill him. Zeus came to Paeon's rescue by turning him into a flower.

Throughout the course of history, few herbaceous ornamental plants have seen a wider and more varied use than peony. Ancients were thought to have used it for flavoring food. In the Middle Ages it was prized for its medicinal properties and used as a cure for a wide array of maladies including gall stones, epileptic seizures, and jaundice. Artists, especially from Southeast Asia, used it as an inspiration and incorporated its image into porcelains, screen prints, paintings and other works of art. Is it any wonder, then, that the ancient Chinese labeled peony "king of all flowers".

Most peonies planted today are hybrids although species of the genus are native to Asia, southern Europe and western North America. Garden peonies usually are bushy herbaceous perennial plants growing up to three feet in height. Peonies have deeply lobed leaves and extravagant (often fragrant) flowers up to six inches in diameter available in a myriad of colors.

Peonies can be classified by plant growth habit or flower morphology. Most garden peonies are herbaceous in growth habit and die back to the ground each winter. However, there are tree peonies that maintain woody stems throughout the year. They are not really trees but grow into small-to-medium sized shrubs that rarely reach more than four to five feet in height in our climate.

Intersectional (Itoh) peonies are the result of a cross between herbaceous and tree peonies, which for many years was thought to be impossible. Japanese horticulturist Dr. Toichi Itoh was the first person successful in making the cross but never lived to see the fruits of his labor. Originally very expensive, Itoh peonies are now readily available and give peony lovers the opportunity to enjoy lavish flowers (including yellow) produced in abundance on a mounded plants three feet in height and width.

Peony cultivars often are classified according to flower morphology. Single flowers have one row of five or more petals surrounding a cluster of yellow stamens that bear pollen. Japanese flowers have one or more rows of petals surrounding flattened, sterile stamens called "stamenoides". If the stamenoids have been transformed into petal-like structures the term "anemone flowered" is used. Semi-double flowers have several rows of petals surrounding pollen-producing stamens. Double flowers have five or more outer (guard) petals with stamens that totally have been transformed into petal-like structures called "petaloids". The latter makes up the bulk of the flower. If the guard petals are relatively short when compared with the petaloids, the result is called a "bomb" flower type.

As mentioned above, September is an ideal month to plant or divide peonies. The latter involves lifting the clump with a spading fork. Excess soil should be washed off the roots to reveal reddish color buds or "eyes" (future growing points). The tops, which probably have started to decline, may be trimmed back also. The clump then can be divided with a sharp knife or hatchet. It is preferred to allow at least three eyes per division.

Peonies need plenty of room and should be planted between three and four feet apart in a fertile garden loam and full sun exposure. Excess shade is a key reason peonies fail to flower.

Since peonies tend to be long lived, adequate soil preparation prior to planting is important. Incorporate well-decomposed organic matter 10 to 12 inches deep in the general area and make individual holes wide enough to spread the roots adequately. Incorporate a modest amount of fertilizer high in phosphorus (e.g. 5-10-5 or bonemeal) and mix it well into the soil.

Planting depth is very important for good growth and flowering of peony. Somewhat shallow planting is preferred since flowering is reduced or inhibited if the eyes are set more than two inches below the surface of the soil.

Peonies can often remain undisturbed in the garden for 20 or more years without a decline in flowering. Vigorous flowering plants have been known to exist in one location for well over 50 years. Division should only be done if growth is poor and plants fail to bloom after years of performing well.

Fertilize peonies with care. Excessive amounts of fertilizer (especially nitrogen) can lead to poor flowering. If top growth slows and plant vigor declines, apply several tablespoons of a complete fertilizer high in phosphorus and potassium (e.g. 6-24-24) about 6 to 18 inches away from the crown. Fall application is preferred although early spring is satisfactory.

Peonies are relative pest free and rarely require the application of pesticides. Bud blight (Botrytis cinerea) is the most troublesome disease and often occurs during cool, wet springs. Strict sanitation including removal of spent plant debris along with proper plant spacing to increase air circulation can help. Fungicides labeled for the control of botrytis can be effective preventatives.

Contrary to popular belief, ants are not necessary for peony flowers to open. Ants are usually present on peony buds because of the sweet exudates produced by the buds and do not help (or hinder) the flower in any way.

To prepare a newly transplanted peony for its first winter it is wise to apply mulch to the base of the plant to prevent heaving damage during periods of alternate freezing and thawing of the soil. Avoid using manure as a mulch unless it is well-decomposed. After establishment, peonies are considered quite hardy and need little winter care.

There are many cultivars of peonies available to the gardening public. Some are new; others are long-time favorites. In a day-and-age where we often think that "newer is better" it is interesting to note that 'Festiva Maxima' still is one of the most popular white-flowered peonies on the market. This "old timer" was introduced into the gardening world way back in 1851.

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REVISED: February 21, 2017