The emerald green arborvitae (Thuja occidentalis "Smaragd") is a popular landscape evergreen shrub. The plant is hardy to USDA hardiness zone 3 and is widely available at nurseries and home improvement stores. The shrub has a tall, slender appearance making it ideal for foundation plantings or, when planted in rows, a privacy hedge.
The emerald green arborvitae tops out at about 15 feet with a width of up to 5 feet. These dimensions represent a mature shrub that is not pruned or trimmed. The short stature and narrow width of the shrub makes it an ideal plant for under overhead power lines and in small spaces.
Growth rates of the emerald green arborvitae are considered slow to medium with average new vertical growth of between 6 and 9 inches per year. This means most shrubs will take about 20 years to reach their mature height.
The average life span of the emerald green arborvitae is about 25 years. This represents the life span under ideal conditions. The shrub’s life can be shortened by salt contamination, deer depredation, disease or insect damage.
Homeowners often prune or shear the emerald green arborvitae in order to maintain the shrub's shape and limit the plant's width. Avoid cutting the top leader or main trunk that extends upward. If the old wood of the tree is cut, the vertical growth of the arborvitae can be adversely affected. Often the shrub is sheared and the new growth of the plant is trimmed off.