Thuja occidentalis is a native North American conifer, also called northern white-cedar, widely planted for dense year-round privacy screens, hedges, and windbreaks. It holds flattened, scale-like, aromatic foliage through severe winters and ranks among the most cold-tolerant evergreen trees in cultivation. Dozens of named cultivars range from narrow columnar forms under 15 feet to broad pyramidal trees exceeding 60 feet.
In the wild it grows in swamps, rocky limestone ridges, and stream banks across northeastern North America, typically on neutral to alkaline soils. In the garden it tolerates clay, periodic wet feet, and alkaline conditions better than most conifers. Deer browse arborvitae heavily in winter and can strip specimens to bare wood where pressure is high. The common name 'tree of life' traces to French explorer Jacques Cartier, whose crew reportedly used the foliage to treat scurvy in the winter of 1535.
Indigenous peoples of northeastern North America used arborvitae foliage and inner bark to treat scurvy, fevers, and rheumatism; the foliage is high in vitamin C. The essential oil contains thujone, which is toxic in quantity, making internal use inadvisable. Topical preparations from leaf extracts appear in traditional practice for warts and skin conditions.
Kabatina Twig Blight
Tips of one-year-old shoots turn yellow then straw-brown, most visibly from late winter through early spring. Tiny black pycnidia appear at the boundary of dead and living tissue. Unlike Phomopsis blight, which kills current-season shoots in summer, Kabatina affects previous-year wood and symptoms are most prominent at or before bud break.
Prune affected shoots 2–3 inches below visible symptoms during dry weather; disinfect cutting tools between each cut with 70% isopropyl alcohol. Avoid overhead irrigation. Apply a preventive copper-based or thiophanate-methyl fungicide in early fall before temperatures drop. Thin dense interior foliage to improve air circulation.
Phomopsis Blight
Irregular brown lesions on leaves, stems, and fruit. Stem lesions can girdle the plant, causing wilting above the infection point. Fruit develops sunken, dark, water-soaked spots that expand and rot rapidly in warm, wet conditions. Small black fruiting bodies may be visible inside older lesions.
Remove and destroy all infected tissue. Avoid overhead irrigation and improve air circulation through adequate spacing. Apply copper-based fungicide at first symptoms and repeat every 7–10 days during wet weather. Rotate out of the nightshade family for at least 3 years and start with certified disease-free transplants.
Armillaria Root Rot
Thinning, yellowing canopy with progressive dieback; white, fan-shaped mycelial mats visible beneath bark at or just below the soil line; honey-colored mushroom clusters appearing at the trunk base or on surface roots in autumn.
No chemical cure exists. Improve drainage and avoid any injury to roots or trunk. Remove severely infected trees along with as much root material as possible. Do not replant susceptible species in the same spot.
Botryosphaeria Canker
Dark, sunken cankers on stems and major branches, most often occurring after drought stress or mechanical wounding. Bark peeled back from affected areas reveals brown, discolored wood beneath. Branch tips wilt and die back progressively inward.
Prune infected branches at least 6 inches below the visible canker margin using sterilized tools, and dispose of all cuttings away from the garden. Reduce plant stress by maintaining consistent irrigation during dry periods and avoiding bark wounds during maintenance. No curative fungicide is available; keeping plants vigorous is the primary preventive strategy.
Root rot
Plants wilt, yellow, and stunt even in moist soil; lower stems and roots turn brown, soft, and mushy and the plant may collapse. Most common in heavy, wet, or poorly drained ground.
Improve drainage and stop overwatering, and never plant too deep. Lift and destroy badly affected plants along with the soil around the roots. Grow in raised or free-draining beds to prevent it returning.