Giant Arborvitae (Thuja plicata), often called Western Redcedar, is a highly sought-after evergreen conifer planted across North America as a fast-growing privacy screen. This species provides dense, attractive foliage that remains green year-round, making it a popular choice for residential landscapes. The ultimate height the tree achieves is highly variable, depending significantly on its geographical location, the specific variety planted, and the overall growing conditions. Understanding its growth potential is the first step in managing its size effectively.
Understanding the Maximum Potential
The maximum size of Thuja plicata is a testament to its origin in the mild, wet conditions of the Pacific Northwest. In its native, undisturbed environment, this species can reach monumental proportions over centuries of growth. Mature specimens in coastal rainforests have been documented soaring to heights of 70 meters (approximately 230 feet) or more. The tallest well-documented individual was measured at 71.5 meters, confirming its status as one of the largest trees in its genus. The species also develops a substantial spread, ranging from 4.5 to 7.5 meters (15 to 25 feet) in diameter at maturity. This maximum potential height defines the upper limit of the species, but it is rarely attained in a typical managed landscape setting.
Typical Growth Rates and Cultivar Sizes
The size observed in residential and commercial settings differs significantly from specimens found in the wild. When planted in cultivation, the species generally matures to a practical height between 15 and 21 meters (50 to 70 feet). This moderate size results from less-than-ideal growing conditions compared to the native rainforest, alongside intentional landscape management.
‘Green Giant’ Cultivar
For homeowners, the popular choice is often a cultivar or hybrid offering a more controlled growth habit, such as the ‘Green Giant’ arborvitae. This hybrid, a cross between Thuja plicata and Thuja standishii, is prized for its rapid growth rate. Under optimal conditions, ‘Green Giant’ can add 0.9 to 1.2 meters (3 to 4 feet) of vertical growth per year once established. This cultivar typically reaches a mature height of 12 to 18 meters (40 to 60 feet) with a spread of 3.5 to 6 meters (12 to 20 feet) in a residential landscape. Its fast growth makes it suitable for quickly establishing a dense screen, but its substantial size requires careful consideration of planting location.
Environmental Factors Affecting Height
The speed and ultimate size a Giant Arborvitae achieves are highly dependent on the quality of its surrounding environment. The rapid growth rate of 3 to 4 feet per year is only achieved when the tree has access to consistent resources. Full sun exposure is beneficial for maximizing height growth, although the species tolerates partial shade. Soil quality is a major determinant, with the most vigorous growth occurring in fresh to moist, nutrient-rich, and well-drained loams. The tree requires consistent water availability and does not tolerate drought or prolonged periods of dry soil, which significantly restricts its annual height increase. If a tree is planted in poor, compacted, or overly dry soil, its growth rate will slow, and its mature height will likely remain at the lower end of the expected range.
Techniques for Size Management
Homeowners can actively intervene to manage the height and width of a Giant Arborvitae planted for screening purposes. The most direct method for limiting vertical growth is a heading cut, which involves removing the tree’s central leader, or main terminal bud. Clipping this stem essentially stops the tree from growing taller. This intervention encourages the tree to become bushier, shifting its energy from vertical extension to lateral growth and density. Once the desired height is reached, the leader can be cut back to a lateral branch. To maintain the width of a hedge, regular shearing of the side branches is necessary, ideally performed in the late winter or early spring before the new growth flush. Avoid cutting back into old, leafless wood, as this species does not reliably regenerate new foliage from old wood, which can leave permanent brown patches.