Thuja occidentalis aka White Cedar

Thuja occidentalis is an evergreen conifer in the cypress family, Cupressaceae. Common names include American arborvitae, eastern white cedar and northern white cedar. It grows wild from Nova Scotia west to Manitoba. Its range runs south to Illinois, Tennessee and North Carolina, with scattered stands in the Appalachians.

This is a dense, conical to narrow pyramidal tree that often broadens with age. In the wild it can reach 40 to 60 feet (12 to 18 m). Garden trees stay much smaller, mostly 20 to 30 feet (6 to 9 m) tall. They spread about 10 to 15 feet (3 to 4.5 m). Trees may have one dominant trunk or several stems. The bark is grey-brown to red-brown with shallow furrows and narrow ridges. On older trees it peels in strips from the trunk and branches.

The tiny scale-like leaves are about 2 mm long. They overlap in pairs and form flat, horizontal sprays. Each scale carries a small resin gland. The foliage is bright green above and paler beneath. Crushed shoots give off a sharp smell like tansy. In winter the leaves often turn yellow-brown or bronze, which some gardeners dislike. This conifer bears no true flowers. Tiny pollen cones sit at the twig tips. The seed cones are oblong, about 1/3 to 1/2 inch long, and ripen from yellow to light brown in summer.

Grow it in full sun or light shade, in moist, deep, well-drained loam. It prefers neutral to alkaline soil but copes with acid soil too. It tolerates clay, wet ground, air pollution and black walnut. Dry soil, deep shade and windy, exposed sites suit it poorly. In heavy shade the foliage thins out badly. Growth is slow, and the tree is hardy to USDA zone 3. Young plants transplant easily, and the species needs little upkeep.

Gardeners use it for hedges, screens, windbreaks and specimen planting. It takes regular clipping but will not regrow from old wood. Songbirds nest in the dense crown. White-tailed deer shelter beneath it in winter and browse the shoots. Breeders have raised many cultivars, from dwarf globes to narrow columns and golden forms. Several keep their green color through winter.

Deer browsing can do serious damage. Leaf miners attack the shoot tips. Bagworms, mealybugs, scale insects and spider mites appear at times. Canker and leaf blight occur now and then. Heavy snow and ice can snap branches, and exposed plants suffer winter burn.

People have cooked the pith of young shoots in soup. The inner bark served as an emergency food, ground into flour. The leafy twigs make a tea rich in vitamin C. However, the essential oil in the leaves is poisonous in large doses. Misuse has caused vomiting, seizures and even death. Pregnant women should avoid the plant entirely. Herbalists use it against warts, and the oil goes into perfumes and insect repellents.