There are only five species of Arborvitae (Thuja). Two species of arborvitaes are native to the U.S., and thrive in U.S. Department of Agriculture plant hardiness zones 2 through 7. Three species hail from Asia and are best suited to USDA zones 6 through 11. Both groups are evergreen trees with thin, soft needles. These low-maintenance plants are valued not only for their long lives, but their attractive pyramidal or rounded shape.
With proper care, an arborvitae will probably outlive you. These majestic trees have long been symbols of strength and can live for centuries, according to the Morton Arboretum. Most live between 50 and 150 years.
Arborvitaes are reasonably low-maintenance plants, but a little extra care can ensure a long, healthy life. Arborvitaes should be planted in full sun to partial shade. In full shade, they become spindly and open. These trees tolerate both acidic and alkaline soil, but they do need well-draining, consistently moist, soil. They should be fertilized in the spring with 3 pounds lawn fertilizer per 100 square feet of soil. The fertilizer should not contain herbicides. One drawback to long-lived arborvitaes is their tendency to turn brown in the fall and winter. Planting them in a protected area can help, but this browning is normal. Arborvitaes rarely need pruning, but you can prune them in spring to control their size or to shape them. Leave some foliage on each branch to promote new growth.
Despite their long lives, arborvitae rarely grow larger than 65 feet tall, depending on the variety. Arborvitae have a moderate growth rate. Under moist conditions, they grow about 12 to 24 inches each year. This moderate growth rate means less pruning for you. Some arborvitae, such as "Hertz Midget" and "Rheingold" have a rounded compact form, making them an ideal choice for small home landscapes.
Pests and Diseases
Besides drought and poorly draining soils, pests and disease can take a toll on arborvitaes, potentially reducing their lifespan. Bagworms are a common problem in many parts of the country. These pests make silk bags among the tree's foliage. To control them, cut the bags off the branches from mid-summer through winter. Drop the bags in hot soapy water to destroy them. Leafminers, the larvae of adult moths, tunnel through the branches, feeding on the foliage. Prune back any affected branches to control them. Bark beetles can be a problem in the West. Once these pests infest trees, they're difficult to control. Plant a variety of trees and shrubs on your property and keep arborvitae healthy since bark beetles tend to infest stressed trees. Arborvitaes are sometimes infected with cankers or root rots, which are usually fatal. To minimize disease problems, select varieties adapted to your area and plant them in well-draining soil. Prune out any diseased portions immediately.