Plant taxonomy classifies peony plants under the genus, Paeonia. Within the Paeonia genus, there are various species and cultivars. The most commonly planted species in North America is Paeonia lactiflora, sometimes referred to as "Chinese peonies." It is with this species that I am concerned below.
Characteristics of Peony Plants
Peony plants bear an attractive, glossy green foliage that reaches 2' to 3' in height with a similar spread. But their popularity is due mainly to their flowers. The most striking peony flowers are the highly fragrant, massive doubles, usually pink, red (for example, 'Red Charm') or white. Other colors and flower types do exist, however. There's even a hybrid with yellow flowers. Peony plants bloom in late spring or early summer. There are peony plants that are indigenous to China, Europe, and the Western U.S.
Problems for Peony Plants
Botrytis blight and other diseases may affect peony plants. In addition to the tips provided below (see "Care for Peony Plants"), watch out that peony plants, grouped en masse, do not become too crowded. Overcrowding reduces air circulation -- an open invitation to disease. If you experience this problem, make a habit of keeping the foliage trimmed back, so that one peony plant does not touch another. A preventive measure is to space peony plants sufficiently when planting (3' to 4' on center).
Sun and Soil Requirements
These fragrant flowers prefer full sun. An exception to this rule applies to growers in zones 8 and 9, where, due to the summer's intense heat, peony plants may profit from partial shade. Grow peony plants in a soil that is fertile and well-drained, with a pH of 6.0 to 7.0.
Planting Peony Plants
Peony plants are growable in zones 2 to 9. Plant bare-root peony plants in fall. All you'll see is a crown with roots dangling beneath it. Dig a shallow hole, spread the roots apart and set the peony plant in the hole. Take note of the buds, which look like the "eyes" on potatoes. The buds should rest only 2" under the surface when you are done planting, otherwise, you may have trouble getting your peony plants to bloom properly. For potted peony plants, a spring planting is suitable.
Uses in Landscaping
Peony plants sometimes are planted individually, sharing perennial beds with other perennials, in which case, due to their large size at maturity, they should be planted in the back row. But peonies are also often planted in groups, side by side, to form a row. Again, their size is such that, when used to form perennial borders in this way, they can make a bold statement in the yard, partitioning it in a manner suggestive of boxwood in formal landscape design.
Care for Peony Plants
Support peony plants with stakes or hoops, as you would tomatoes. The large blooms get heavy, especially after a rain. Trimming back and disposing of the foliage in autumn helps prevent the disease, botrytis blight. Other diseases may cause a gradual decline in peony plants. If you see one specimen is stunted while the peony plants around it are doing fine, remove and destroy that plant, lest it infect the others. Mulch (2" to 3") peony plants in the fall, removing the mulch in spring.
Pronunciation of "Peony" Plants and Word Origin
The standard pronunciation is pee'-uh-nee (accent on the first syllable). However, many people place the accent on the second syllable: pee-oh'-nee. As is often the case with anglicized versions of Latin words, rulings on what should be the standard pronunciation seem rather arbitrary. The word derives from the Latin genus name, Paeonia, which, in turn, derives from a figure in Greek mythology, Paeon (see below). If you want to be safe, stick with the standard pronunciation: pee'-uh-nee.
More on Peony Plants
Often, when we see pictures of huge, beautiful flowers in books, we assume they come from the tropics. Happily, Mother Nature made an exception with peony plants. Cold hardy to zone 2, deep in the frozen North, peony flowers needn't take a backseat to any tropical bloom.
Nor have people failed to notice the exceptional nature of this flower. For hundreds of years, long before garden catalogs, from one corner of the globe to another, peony plants have been grown and admired. In China, they were even prized for their medicinal qualities. E.g., white peony root was used to treat liver problems. The Greeks and Romans also found medicinal uses for peonies. However, in excessive doses, all parts of peony plants are toxic.
As is fitting for such a lovely flower, peony plants derive their name from a Greek myth. Paeon, a student under Aesculapius, god of medicine, was well aware of the medicinal qualities of peony plants. He used them to heal a wound suffered by the god, Pluto. The upstaged Aesculapius wasn't pleased and threatened retribution, but, in one of those charming metamorphoses sprinkled liberally throughout the pages of Greek mythology, Pluto saved Paeon's life: he turned him into a peony plant.
If possible, try to grow peony plants near entrances, where their fragrance can be most readily enjoyed. While their blooming period is tantalizingly short, even the foliage of peony plants is sufficiently attractive to warrant planting in a cozy corner near the doorstep. The peony plants with double flowers tend to be the most fragrant. To extend the blooming season, "stagger" your selection of varieties. That is, select some that bloom early, others late, and still others that bloom sometime in between.
As if stunning beauty and heady fragrance weren't enough, peony plants are also exceedingly long-lived. In fact, they have been known to live for 100 years or longer. Peony plants are unlike many other perennials, in that they do not need to be divided on a regular basis. In fact, they dislike being disturbed. If you'd still like to try dividing them (to increase your stock), do so in fall.