Though a few species peonies may be found through specialists’ catalogs and seed exchanges, most garden peonies are hybrids. The basic types are herbaceous and tree peonies, both descended from Chinese species. A new third category, the intersectional hybrids, combines the best traits of herbaceous and tree types. All peonies are extremely long-lived plants of significant size; they provide choice cut flowers and are a mainstay of big perennial borders.
Plant peonies in fall, either as bare-root plants or from nursery containers. Ideally, the planting site for peonies should be deeply dug at least several days before planting. Work in plenty of compost, especially in heavy soil, and incorporate a high-phosphorus fertilizer; then allow the soil to settle before planting.
Peonies of all types can be grown in large (18–24-in.) containers. Replant every third autumn in the same or a slightly larger pot, replacing most of the soil when you do.
Perennials. Well-grown clumps reach 2–4 ft. tall and wide. Large, glossy, deep green, attractively divided leaves are an effective background for the plants’ spectacular spring or early-summer flowers and look good throughout summer. Flower colors range from pure white through cream to pink and red; some of the reds are very deep, with chocolate brown overtones. Depending on the variety, blossoms range from 2 in. to as much as 10 in. across; many have a perfume similar to that of old-fashioned roses, though in some varieties the scent is either unimpressive or absent. In form, they fall into three basic categories: single or semidouble, with one or two rows of petals; Japanese, with a single row of petals and a large central mass of narrow petal-like segments called staminodes; and double, with full flowers composed of many petals. Varieties are too numerous to list.
Herbaceous peonies bloom well only where they get an extended period of pronounced winter chill. Summer heat is not a problem for the plants, but their flowers do not last as well where spring days are hot and dry. In such areas, choose singles, semidoubles, and Japanese varieties, as they bloom before the season heats up; also give plants some afternoon shade and be sure they have adequate water. (Japanese types in particular do well in the warmest zones.) In the mildest-summer parts of Zones 1–7, where these plants grow best, they thrive in full sun. Provide support for very large or double varieties, which can become so heavy with water during spring rains that they fall over.
Divide herbaceous peonies only to increase your stock. Dig clumps in early fall, hose off soil, and divide into sections, making sure that each has at least three eyes; these appear at the tops of root clusters, at or near the bases of the past season’s stems. Plant immediately to allow plants time to put down roots before the onset of freezing weather. Transplants may take a year or two to establish before blooming.Paeonia, Intersectional Hybrids
Woody perennials. Moderate growth rate to about 3 ft. high and wide. Attractive leaves resemble those of tree peonies. Compared with herbaceous and tree peonies, intersectional hybrids produce more flowers and bloom over a longer period, sport better-looking foliage throughout the growing season, and have superior resistance to botrytis. Flowers may be single, semidouble, or double in single and multicolored shades of lavender, pink, red, copper, yellow, or cream. There are many varieties to choose from, including the new Itoh hybrids, named for the first person to successfully cross a herbaceous peony with a tree peony. Intersectional hybrids require less winter chill than herbaceous peonies.
Deciduous shrubs. Slow growth to 2–6 ft. tall and eventually as wide, with handsomely divided blue-green to bronzy green leaves. Single to double flowers, typically very large (to 10–12 in. across), appear in spring. These peonies seldom show their full potential until they have spent several years in the garden, but the spectacular results are worth the wait.
Catalogs offer named varieties of Japanese origin in white and shades of pink, red, and purple. These are generally semidouble and display their flowers well. Some of the older European hybrids in pink and yellow are fully double, with flowers so heavy that they hang their heads. More recent hybrids come in yellow, copper, and a coral that approaches orange; all result from crosses of P. suffruticosa with P. delavayi and P. d. lutea. These bear semidouble blooms that face outward and upward.
Tree peonies require much less winter chill than herbaceous peonies. The large flowers are fragile and should be sheltered from strong winds. Snip off blooms when they fade. After leaf drop in fall, prune to remove dead wood and to control the height of mature plants; do this by removing about half the current season’s growth on the tallest branches that have bloomed, always making your cuts just above an outward-facing side branch. In coldest climates, protect from winter sun and wind with a burlap curtain.
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