Platycladus orientalis aka Oriental Arbor Vitae

Platycladus orientalis is an evergreen conifer in the cypress family, Cupressaceae. Gardeners know it as oriental arborvitae, Chinese arborvitae, oriental thuja or biota. Older references list it as Thuja orientalis or Biota orientalis, and some nurseries still use those names. It grows wild in northern and east-central China and in Korea. Its range also reaches Manchuria and the Russian Far East.

In gardens it forms a dense cone or column, either as a large shrub or a small tree. Most plants reach 15 to 25 feet (4.5 to 7.5 m) tall and 10 to 15 feet (3 to 4.5 m) wide. In the wild it can reach 60 feet (18 m). Young plants hold a tight, tidy shape. Older plants grow more open and irregular, and they sometimes need tying. Many trees have several trunks.

The branchlets stand upright in flat, vertical sprays, which makes the plant easy to recognise. The leaves are tiny triangular scales with a groove on the back. They start yellowish green and darken with age. In cold winters they may turn bronze or brownish. Bruised foliage gives off a scent. The thin, reddish-brown bark peels away in long fibrous strips.

The plant bears separate male and female structures, but the flowers have no ornamental value. The egg-shaped cones grow up to 3/4 inch (2 cm) long. They start fleshy and bluish green, then harden and turn brown. Each of their six to eight thick scales ends in a small hooked horn. Ripe cones split open and can look like small roses.

Oriental arborvitae does best in full sun but accepts light shade. It needs well-drained soil and good air flow. It handles sand, loam and clay, provided clay sits on a slope that drains well. It is pH adaptable. Wet or boggy ground suits it poorly. Once established, it copes well with drought, but it tolerates salt spray badly. Most sources rate it hardy in USDA zones 6 to 10. It may survive zone 5 in a sheltered spot away from harsh winter wind.

Gardeners use it as a specimen, hedge, screen or foundation plant. It also appears in mass plantings, highway medians and cemeteries. It accepts regular trimming but will not regrow from old wood. Dwarf and golden cultivars appear in gardens far more often than the species itself. The wood lasts well in soil, and the young branches yield a yellow dye. Chinese herbal medicine uses the leaves and seeds.

Healthy plants have few serious problems. Spider mites and bagworms are the main pests. Scale insects, aphids, caterpillars, borers and mealybugs can also appear. A fungal blight can brown the inner twigs, and sun and good air flow help prevent it. Heavy snow and ice can snap branches. The seeds are edible once their bitterness is removed. The leaves are toxic if eaten, and the plant can trigger skin allergies in sensitive people.