Japanese pieris

Identification and origin

Pieris japonica belongs to the heath family, Ericaceae, along with rhododendrons and azaleas; it was long known as Andromeda japonica. It grows wild in mountain thickets in Japan (from the center to the south of the archipelago), Taiwan, and southeastern China.

It is a slow-growing evergreen shrub with an upright, rounded, dense habit. It usually reaches 8–10 ft tall and 6–8 ft wide, but takes ten to twenty years to reach mature size and can grow larger with age; dwarf cultivars also exist. The leathery leaves, 1–4 in long, are crowded in rosettes at the branch tips; they are dark green and shiny above, paler beneath, with finely toothed margins. In spring, new growth flushes bronze, pink, or coppery red before turning green. Older plants have reddish-brown, scaly, fissured bark.

Flower buds form from late summer on and stay decorative all winter, often tinged red. In spring they open into drooping clusters 3–6 in long of small, fragrant, white, urn-shaped flowers that recall lily-of-the-valley and feed early pollinators. The fruits are small, dry, brown capsules that persist into winter. Deer tend to leave it alone.

Among the many cultivars: ‘Mountain Fire’ (vivid red new growth), ‘Flaming Silver’ (red young leaves that become edged in silver), ‘Dorothy Wyckoff’ (red buds, pale pink flowers), ‘Valley Rose’ (pastel pink flowers), ‘Debutante’ and ‘Prelude’ (compact, 20 in – 3.5 ft), ‘Cavatine’ (a low mound), and ‘Carnaval’ (variegated foliage).

Light

Partial shade suits it best, ideally the light, dappled shade of taller trees. It tolerates sun, but avoid all-day full sun, especially in hot gardens. In a sunny, exposed site the young leaves scorch easily, and wind and winter sun also burn the foliage. A well-sited plant, in shade or partial shade, is also much less susceptible to lace bugs.

Watering

The soil should stay consistently moist without ever becoming soggy. Check moisture deep in the soil, especially during hot, dry summers: drought weakens the plant quickly. Soil that stays waterlogged, on the other hand, leads to root rot. A good organic mulch keeps the roots from drying out.

In a container, the mix dries much faster than garden soil, even in winter when the wind blows: it can take several waterings in a row to moisten the whole root ball. Where tap water is hard, use rainwater when you can and keep tap water as a backup.

Potting mix

Plant it in acidic soil, ideally pH 5 to 6, moist but well drained, rich in organic matter, with a loamy or sandy texture. It tolerates neither lime nor waterlogging. In alkaline soil, from pH 7 up, growth is poor and the leaves turn yellow: have your soil tested if in doubt. Use a fertilizer made for acid-loving plants (azaleas, rhododendrons, blueberries) and mulch every fall.

Temperature

Japanese pieris is hardy in USDA zones 4b to 8b and survives winters that drop to around 5–14 °F. Shelter it, however, from cold, drying winds, which burn the evergreen foliage. Young plants sometimes need winter protection. In a container, the roots near the sides freeze more easily: in an exposed garden, wrap the pot in burlap or another insulating layer.

Repotting

Compact varieties make fine container plants. Use a soil-based mix for acid-loving plants and a pot with drainage holes sized to the root ball: do not put a small plant in a very large pot, and step up in size gradually. Repot every few years in spring, either into a larger pot or back into the same one after refreshing the mix. In the other years, scrape away about 2 in of mix from the surface in spring and replace it with fresh mix blended with a slow-release fertilizer.

Pruning

Minimal pruning is enough. The plant tolerates cutting, but it blooms on old wood and its buds form in late summer, so any pruning after that removes the next season’s flowers. Prune right after flowering, and only when needed, for example to remove dead wood or rein in an overlong shoot.

Propagation

Propagate by stem cuttings. Take softwood cuttings in early summer or semi-hardwood cuttings in late summer. Bottom heat is sometimes needed to get them to root.

Common problems

• Leaves stippled with pale dots, then yellowing: lace bugs, which feed on the undersides of the leaves; look there for their spiny cast skins and small varnish-like spots of excrement. They overwinter as eggs in the evergreen leaves and can defoliate the plant. A site out of full sun limits attacks; any treatment must reach the leaf undersides.
• Yellow leaves, weak growth: soil that is too limy or alkaline.
• Wilting, dying branches: Phytophthora root rot, encouraged by poorly drained soil; more rarely honey fungus.
• Spots on the leaves: fungal leaf spot.
• Scorched foliage: cold wind, winter sun, or full sun on young growth.
• A plant that languishes for no visible reason: nematodes in the soil.

The same symptom can have several causes: before treating, check exposure, moisture, soil pH, and the undersides of the leaves.

Toxicity

All parts of the plant are highly poisonous if eaten: leaves, flowers, nectar, and sap contain grayanotoxins (andromedotoxin). In people, ingestion can cause tingling, drooling, nausea, vomiting, diarrhea, sweating, abdominal pain, headache, weakness, convulsions, and heart problems, sometimes fatal. Dogs, cats, and horses are affected too: vomiting, diarrhea, depression, excessive salivation, weakness, low blood pressure, coma, cardiovascular collapse, and death; a few leaves can cause serious problems. Rodents, rabbits, and tortoises are also at risk. The plant does not cause contact dermatitis, but wear gloves when handling it and, if any is swallowed, contact a doctor, a poison control center, or a veterinarian.