Thuja occidentalis, commonly known as northern white cedar, eastern white cedar, arborvitae or swamp cedar, is native to northeastern North America. The name "arborvitae" means "tree of life," and dates from the 16th century explorer Jacques Cartier, who learned from natives how to use the tree's foliage to treat scurvy. Thuja is a widely planted ornamental tree in the U.S.
Thuja is a fine-textured, evergreen, symmetrical tree that grows 25 to 40 feet tall, with a 10- to 12-foot spread. It has a slow growth rate. Its less-than-2-inch green leaves are simple, scale-like and fragrant. Branchlets form in horizontal sprays with leaves overlapping each other, forming rope-like shoots. They are brown in winter, but some cultivars have been developed with green winter foliage. Thuja fruit consists of small cones that are not very noticeable unless heavily set. Its bark is gray on the surface and red-brown in the narrow furrows.
Grow thuja in full sun for the best appearance. Partial-shade-grown thujas become thin and open-looking. Thuja is easily transplanted and prefers moist, deep, loamy soil and is tolerant of acidic and alkaline conditions. Thuja likes humid air, is somewhat tolerant of wet soils and can be sheared to maintain shape and size. The trees are hardy to USDA zone 3.
Thuja trees are used as hedges, screens and windbreaks. Small cultivars are suitable as foundation plantings (near structures). Placed at the corner or edge of an area, thuja softens the view.
The cultivars of thuja include several shrubs, such as Compacta Erecta and Hetz Junior. Nigra has dark green foliage in winter and Rheingold has a rounded form with yellow to bronze new growth. Emerald thuja is a popular commercial variety with year-long, bright emerald foliage. Emerald grows 15 feet tall and 5 feet wide, and is good for hedging, barriers and as an accent plant.
Problems of thuja include spider mites, leaf miners and bag worms. In very harsh locations, foliar burn may be an issue. Heavy snow loads often cause damage to thuja trees, and deer can be a pest as well. Your local county extension office is a good source regarding disease and pest identification and management.