Thuja plicata aka British Columbia Red Cedar

Western red cedar, Thuja plicata, is a large evergreen conifer in the cypress family, Cupressaceae. It also goes by giant arborvitae and western arborvitae. Its home range runs along the west coast of North America. It grows from southern Alaska and western British Columbia south to northern California. Inland it reaches northern Idaho and western Montana. It has naturalised in Britain and is the provincial tree of British Columbia.

This is the largest member of the cypress family. Garden trees usually reach 50 to 70 feet (15 to 21 metres) tall and 15 to 25 feet (4.5 to 7.5 metres) wide. Some cultivated plants stay nearer 20 to 30 feet (6 to 9 metres). Wild trees can top 150 feet (46 metres), and the oldest known specimens exceed 1,000 years. The form is a narrow pyramid with a buttressed base. Branches often keep foliage down to the ground. They droop slightly and sweep upward at the tips.

The tiny scale-like leaves sit in opposite pairs, forming flat, fern-like sprays. They are glossy dark green above. Below, white stomatal bands make a butterfly or bowtie pattern. Crushed foliage gives off a scent like tansy. In winter the foliage can turn yellowish-green or brownish. The thick bark is reddish brown to grey and fibrous. It peels away in long narrow strips.

The tree bears cones rather than flowers. Male and female cones grow on the same plant. Small reddish pollen cones at the shoot tips release yellow pollen in spring. The upright, egg-shaped seed cones are about half an inch (1.3 cm) long. They ripen from green to brown in autumn and release small winged seeds.

Plant western red cedar in full sun or partial shade. Heavy shade makes it thin and open. It likes moist, well-drained, fertile soil rich in organic matter. It copes with acid to alkaline soils, clay, and somewhat wet ground. It dislikes drought, dry winds and hot, humid summers. It is hardy in USDA zones 5 to 8 and rated H6 in the UK. Growth is moderate to fast, up to 2 to 3 feet a year.

Gardeners use it as a specimen tree for large spaces, or as a hedge, screen or windbreak. It also suits rain gardens and pond or stream edges. It tolerates trimming, so young trees can be kept as a hedge. Native peoples of the Pacific Northwest built canoes, houses and tools from its wood. They wove the bark and roots into baskets, rope, mats and clothing. Today the decay-resistant timber goes into siding, shingles, decks and fences. Birds and small mammals shelter in it.

Problems include bagworms, leaf miners, spider mites, scale insects and conifer aphids. Possible diseases are honey fungus, Phytophthora root rot and thuja blight. Heavy snow can break branches, and deer often browse the foliage. The RHS lists the plant as harmful if eaten and as a skin allergen. Other sources record the inner bark as edible after drying and grinding into flour.