The plants commonly known as arborvitae, a Latin term meaning “tree of life,” are popular evergreen conifers belonging to the genus Thuja. These trees are widely sought after for landscaping due to their dense, scale-like foliage and naturally pyramidal or conical growth habit, making them excellent choices for privacy screens and accent plantings. While the name “arborvitae” is used broadly in the nursery trade, the number of true, naturally occurring species is quite small. The diversity seen in gardens comes from the hundreds of cultivated varieties, known as cultivars, that have been bred from a few parent species.
The Five Recognized Species of Thuja
The genus Thuja contains only five currently recognized species, divided into two species native to North America and three species originating in East Asia. The two North American species are the most commonly encountered in global horticulture, while the three Asian species are less frequently seen outside of specialized botanical collections.
The Asian species include Thuja koraiensis (Korea and China), Thuja standishii (Japan), and Thuja sutchuenensis (central China). T. sutchuenensis was once thought to be extinct before its rediscovery in the late 20th century. These Asian types are generally smaller than their North American relatives and tend to be less tolerant of extreme climate variations. Consequently, the vast majority of plants sold as arborvitae worldwide are derived from the two North American species, T. occidentalis and T. plicata.
The Versatility of Eastern Arborvitae (Thuja occidentalis)
The Eastern Arborvitae, Thuja occidentalis, is the species most often associated with the common name and is native to the cold-tolerant regions of Eastern North America. It is naturally a smaller tree than its western counterpart, typically reaching 40 to 60 feet in the wild, but often remains much shorter in cultivation. This species is valued for its hardiness and ability to thrive in a wide range of climates, making it the preferred choice for dense hedging and year-round screening.
The true diversity of this plant is found in its hundreds of cultivars, which are bred to control size, shape, and foliage color. Pyramidal forms are popular, such as ‘Emerald Green’ (‘Smaragd’), which maintains a narrow, dense, and columnar shape with deep green foliage throughout the year. ‘Nigra’ is another widely used selection, known for its dark green color that resists the bronzing often seen in other varieties during the cold winter months.
Other cultivars are specifically bred for their unique growth habits, providing options beyond the standard screening plant. ‘Techny’ (also known as ‘Mission’) is a broader, denser pyramidal form suitable for large-scale windbreaks. For smaller gardens, compact and spherical forms are available, such as ‘Golden Globe’ and ‘Hetz Midget’, which grow into tight, globe-like shrubs requiring little to no pruning. Selections like ‘Rheingold’ or ‘Yellow Ribbon’ display vibrant golden-yellow new growth.
Western Arborvitae and Giant Attributes (Thuja plicata)
In contrast to the moderate scale of the eastern species is Thuja plicata, commonly known as Western Red Cedar or Giant Arborvitae. This species is native to the Pacific Northwest, where it naturally develops into one of the largest trees in the cypress family, capable of reaching over 200 feet in its native habitat. Even in garden settings, it grows rapidly, often adding two to three feet of height per year, making it the superior choice when maximum height and fast screening are the primary goals.
The wood of T. plicata is naturally resistant to decay and rot, contributing to its longevity and superior overall health compared to other evergreens. This resistance means the species tends to be less susceptible to common pests and diseases that can afflict other arborvitae. Its massive size and vigorous growth rate make it a popular selection for large property lines or commercial landscapes needing a significant windbreak.
A commonly planted cultivar is ‘Green Giant’, which is actually a hybrid cross between T. plicata and T. standishii, though it shares the giant attributes of the western species. This hybrid maintains the fast growth rate and disease resistance but often exhibits a more uniform, dense pyramidal shape than the wild species. Other notable cultivars include ‘Atrovirens’, prized for its consistent dark green foliage that remains attractive year-round, and ‘Virescens’, a narrow selection that holds a vivid green color even in winter. These selections allow gardeners to harness the impressive scale and durability of the Western Red Cedar in a more controlled, landscape-appropriate form.