What Is Thuja Occidentalis?

The Eastern white cedar, Thuja occidentalis, is a native evergreen tree that grows from Kentucky and parts of South Carolina north into Canada. Reaching 30 to 50 feet tall and 10 to 15 feet wide at maturity, it is conical shaped and does well in cold climates. Thuja occidentalis tolerates acid and alkaline soils, can be cut to maintain its shape, and does well in moist air and full sun. It is also called the arborvitae, or the northern white cedar.

Eastern white cedar grows dense and compact, making it a good choice for windbreaks, screens and hedges. The tree responds well to pruning and shearing, so it can be maintained at a preferred height. It has a variety of cultivars, which can be used as foundation plantings or as a green plant during the winter. A member of the cypress family, it is often used at entranceways to accent its narrow columnar shape.

White cedar does not like shady locations. Full sun or partial shade is required for the plant to do well. It has a high tolerance to urban heat and pollution, and grows in USDA Zones 2 through 8. The tree likes well-drained loamy soil, and does not do well with wet feet. White cedar is tolerant of a variety of soils, so it has a potential wide growing range, but it is listed as endangered in Massachusetts, Indiana and New Jersey. It does not have threatened or endangered status with the federal government.

Thuja occidentalis is a perennial tree with a conical shape and dense evergreen foliage that turns yellow-brown in the winter. The tree frequently has multiple trunks, with branches extending out horizontally from the trunks. The University of Connecticut Plant Database describes the smell of crushed foliage as "tansy-like." Leaves are scale-like, and the seed-bearing cones are very small, especially when compared to pine cones. Cultivars provide much more variety than the main Eastern white cedar.

Varieties of Thuja occidentalis include the 'Hetz midget' cultivar, which grows in a rounded form 3 feet high by 3 feet wide. For a taller variety, the columnar 'Nigra' towers 20 feet high and 4 feet wide. The popular 'Emerald' variety keeps its green color in winter, and has a narrow 4-foot wide growth habit and moderate 12-foot mature height. For a pyramid-shaped offering, 'Peabody' spreads 5 feet wide by 10 feet high with golden foliage rather than the usual green.

Thuja occidentalis has two main liabilities: deer love to eat it, and snow accumulation causes a lot of branch separation. The tree is also threatened by bagworm infestations and the damage these pests do to new leaves while feeding. Leaf miners and spider mites are other known pests. When white cedars age, they can separate at the base, losing the uniform look of a row planting. As a member of the cypress family, the tree is also subject to heartwood rot, which makes the tree less vigorous.