Northern whitecedar (Thuja occidentalis, L. 1753)

Identity

Northern whitecedar (Thuja occidentalis L., 1753) is an evergreen conifer of the genus Thuja, in the Cupressaceae family. Other established names include Eastern white-cedar, Swamp cedar, White cedar, Arborvitae and American arborvitae. Linnaeus described it in Species Plantarum in 1753, using trees already cultivated in Europe for several generations. ^{2 1}

White cedar names can mislead: this tree belongs to Thuja, whereas true cedars, Cedrus, belong to the separate Pinaceae family. Arborvitae translates Latin arbor vitae, “tree of life,” and recalls a 16th-century episode. Explorer Jacques Cartier is said to have learned from Indigenous peoples how to treat his crew’s scurvy with a decoction of vitamin C-rich foliage. ^{4 3}

Recognition

Mature Thuja occidentalis commonly reaches 12–20 m (39–66 ft) tall, spreading 3–5 m (10–16 ft) in well-exposed sites. Growth is very slow in the first few years, then settles around 15–20 years, when its conical to columnar outline becomes established. ^{4 6}

Flattened, overlapping sprays carry fine, scale-like foliage that releases an aromatic scent when crushed. Leaves often turn bronze-brown in winter before returning to green in spring, helping distinguish normal seasonal dormancy from disease. ^{6 5}

Both sexes occur on one tree: Northern whitecedar is monoecious. Small, upright, egg-shaped cones on short branchlets change from green to light brown by late summer, releasing two winged seeds per scale. ^{5 7}

Useful taxonomy

For the wild species, POWO and IPNI retain the accepted name Thuja occidentalis L., published in 1753. Several historical synonyms remain in older horticultural literature:

• Thuja canadensis K.Koch, historical synonym
• Cupressus arborvitae O.Targ.Tozz., historical synonym
• Thuja odorata Marshall, historical synonym
• Thuja procera Salisb., historical synonym

The full accepted scientific name provides a stable reference because horticultural trade adds another layer of uncertainty. Numerous dwarf and columnar cultivars are sold by cultivar name alone, without always identifying the parent species. ^{1 3}

Other members of Thuja include North American western redcedar, Thuja plicata, and Japanese Thuja standishii. All three have similar scale-like foliage, but Thuja occidentalis is the smallest and the only one adapted to severe continental winters. Thuja plicata inhabits the temperate Pacific coast, sheltered from severe frost. ³

Habitat and range

Eastern and central Canada connect its native range with the northeastern and north-central United States. Isolated populations extend along the Appalachians to North Carolina and Tennessee. It colonizes calcareous swamps and peatlands, moist streambanks, sheltered rocky ledges and cliffs. ^{4 6}

Around the Great Lakes, exposed limestone ledges support stunted, extremely slow-growing trees among the oldest in eastern North America. In favorable moist habitats, the species can exceed four centuries. ⁴

European cultivation began in the 16th century and continues widely for ornamental trees and hedges. The species has also naturalized locally in some temperate parts of central Europe. ^{4 8}

Life cycle and reproduction

Spring brings conifer “flowering,” or pollination. Tiny male cones release pollen before female cones form on the same branches. The female cones ripen in late summer, changing from green to light brown before opening. ⁵

Early height growth is remarkably slow: seedlings average only about 8 cm (3 in) a year in their first years, accelerating once their root systems are well established. ⁴

For cultivated forms, cuttings of semi-ripe shoots taken in late summer preserve cultivar characteristics more reliably than seed, rooting within a few weeks. Seed propagation, used for the wild species, requires several months of cold stratification and gives slow, uneven germination. ⁷

Uses and risks

Light, soft wood with strong resistance to decay, despite lacking resin, has long been used in North America for canoes, fence posts and roof shingles. ⁷

Indigenous peoples traditionally used the foliage for fever, coughs and rheumatism. Modern essential oil, rich in thujone, is included in external wart preparations but remains toxic when large quantities are swallowed. Convulsions and deaths have been reported after poorly controlled internal use, and use during pregnancy is prohibited. ⁷

Unlike concentrated essential oil, the foliage is not classified as toxic to cats and dogs. Ornamentally, Northern whitecedar is chiefly a hedge and screening tree, valued for cold hardiness down to USDA 2 and tolerance of repeated clipping. ⁶

Varieties, look-alikes and related plants

Hundreds of cultivars are distinguished in horticulture. 'Smaragd' (Emerald Green) dominates compact columnar hedging; 'Brabant' grows faster for quick screening; 'Rheingold' has golden foliage that turns coppery in winter; and the dwarf globe 'Danica' suits small gardens and containers. ^{5 6}

Confusion most often involves western redcedar, Thuja plicata, with broader, drooping branches and a much greater mature size than Thuja occidentalis. False cypresses, Chamaecyparis, have similar scale-like foliage but a different scent when crushed. Junipers, Juniperus, are distinguished by fleshy berries rather than small dry cones.

Main sources

• Plants of the World Online / Kew, Thuja occidentalis L.
• International Plant Names Index, Thuja occidentalis L.
• Integrated Taxonomic Information System, Thuja occidentalis L. (TSN 505490)
• USDA Forest Service, William F. Johnston, Northern White-Cedar (Thuja occidentalis), original Silvics chapter; archived 14 October 2025
• Missouri Botanical Garden Plant Finder, Thuja occidentalis
• NC State Extension Gardener Plant Toolbox, Thuja occidentalis
• Plants For A Future, Thuja occidentalis
• Tela Botanica / bdtfx reference database, Thuja occidentalis