Chinese peony

Identification and origin

Paeonia lactiflora belongs to the peony family, Paeoniaceae. Its natural range covers northern and central China, Manchuria, Inner Mongolia, Mongolia, and the Russian Far East, from the Chita region to Primorye.

It is a herbaceous perennial that forms a clump from thickened, tuberous roots. All the foliage dies back in winter and regrows in spring from pink or white buds at the top of the roots, which gardeners call “eyes.” The large, dark green leaves are compound, often with nine elliptic to lance-shaped leaflets. The plant reaches 20 in – 3.5 ft tall and as wide.

The wild form bears fragrant white or pale pink flowers about 4 in across, with pale yellow stamens, in early summer. The fruits are follicles that split open to release a few fleshy black seeds.

Most herbaceous peonies sold in garden centers are cultivars of this species, grouped as Lactiflora cultivars; their often fragrant flowers reach 6 in. They are classified by flower form: single (one ring of petals around the stamens), Japanese (petals surrounding flattened, sterile stamens), anemone, semi-double, double, or bomb. Classics still widely grown include ‘Sarah Bernhardt’, a reliable, fragrant double pink; ‘Festiva Maxima’, a double white flecked with red, introduced in 1851; ‘Monsieur Jules Elie’ and ‘Felix Crousse’, both pink; and ‘Bowl of Beauty’, with broad pink petals around a pale yellow center.

Light

The more sun a peony gets, the better it blooms: aim for six to eight hours of direct sun a day. Shade reduces the number of flowers and encourages powdery mildew. Watch for shade that creeps in over the years as nearby trees grow. In warm regions, though, a little afternoon shade helps.

Choose an airy spot, not right up against a wall, and sheltered from strong winds that knock the flowers over.

Watering

Early in the season, while stems and buds are forming, the plant needs plenty of water. After that, water when the soil starts to dry at the surface and let it dry somewhat between waterings: the fleshy roots rot in soil that stays wet. Avoid overwatering, which also encourages botrytis blight.

Potting mix

It needs fertile soil at least 12–18 in deep, well drained, with a near-neutral pH; it adapts to clay, loam, or sand as long as water does not sit. Avoid low spots. Before planting, work well-decomposed organic matter into the soil to a depth of 10–12 in.

Fresh manure must never touch the roots or shoots, as it can rot them; composted manure, on the other hand, can be spread on the surface. On an established plant, apply a little complete fertilizer high in phosphorus and potassium in spring or fall, at least 6 in away from the stems. Too much nitrogen gives leaves at the expense of flowers.

Temperature

It is a very hardy plant, grown in USDA zones 3 to 8 and at its best in zones 5 to 7. Winter cold is essential: the roots need a cold period to form flower buds. Where winters are mild, it languishes and blooms poorly; choose low-chill cultivars such as ‘Sarah Bernhardt’, ‘Festiva Maxima’, ‘Felix Crousse’, or ‘Monsieur Jules Elie’, plant the eyes no more than 1 in deep, and do not mulch in winter.

In cold climates, mulch the first year with 2–3 in of leaves or straw once the ground freezes, so freezing and thawing do not heave the young plant; remove the mulch in spring.

Repotting

Peonies are grown in the ground and dislike being moved. Bare-root divisions are planted from late summer to early fall; container plants in spring or early summer. Choose roots with three to five eyes: with fewer they can rot; with more, the flowers stay small.

Depth is critical: no more than 2 in of soil should cover the eyes. Planted too deep, a peony makes fine foliage but does not bloom. For a potted plant, keep the crown at soil level and tease out the roots if they circle. Space plants 3–4 ft apart and keep them away from tree roots and lawn. Expect one to two years before the first flowers.

Pruning

Cut faded flowers and their stems back to the foliage line. For bouquets, cut when the outer petals unfold, without taking too many leaves, which feed next year’s bloom. In the first year, remove the buds to help the roots establish.

Big double flowers often flop after rain: set up peony hoops in spring, before the clump gets too large. In fall, cut all stems at ground level and throw them away rather than composting them: it is the best prevention against botrytis.

Propagation

Division is the method used in the garden. It is not needed to keep a plant vigorous: divide only if growth declines, and never a plant less than three years old. Do it in early fall: cut the stems, lift the clump with a spading fork, shake and wash off the soil to see the eyes and the natural division points. Cut pieces with three to five eyes and three or four thick roots, replant them at the right depth, and mulch. A divided plant takes two to three years to bloom fully again.

Common problems

• No flowers: planted too deep, shade, a young or recently divided plant, excess nitrogen, winters too mild, disease, or thrips.
• Young stems that wilt and collapse in spring, buds that turn brown: botrytis blight, favored by cool, wet springs; remove affected parts.
• White powdery coating on leaves: powdery mildew, more common in shade and in poorly ventilated spots.
• Spotted leaves: leaf spots or anthracnose; clean up thoroughly in fall.
• Deformed flowers that do not open: thrips, or botrytis on the buds.
• A plant that gets smaller and discolored year after year: virus; remove it.
• Ants on the buds: harmless; they feed on the sugary nectar.

The same symptom can have several causes: check planting depth, sun exposure, and the condition of the roots before acting.

Toxicity

Peonies are listed as toxic to dogs, cats, and horses. Their toxic principle, paeonol, can cause vomiting, diarrhea, and depression. Keep pets away from plants and cut stems, and contact a veterinarian if one is eaten.