Arborvitae (Thuja species) are popular evergreen trees and shrubs often used for privacy screens and landscaping. Understanding the annual growth rate is important for planning a yard’s aesthetic and function. Growth rate, measured as the vertical increase in height per season, is highly variable and determined by the tree’s genetics and environmental conditions.
Annual Growth Rates by Specific Variety
The most significant factor influencing an arborvitae’s yearly growth is the specific cultivar chosen, as each variety has a unique, genetically programmed potential. The ‘Green Giant’ arborvitae (Thuja plicata x standishii) is the speed champion, classified as a rapid grower. Under optimal conditions, a young, established ‘Green Giant’ can easily add between three and five feet of height each year. This makes it a preferred choice for quickly establishing a dense privacy barrier.
Varieties like ‘Techny’ (Thuja occidentalis ‘Techny’) and ‘American Pillar’ fall into the moderate to fast-growing class, typically putting on two to four feet of growth annually. These options provide a fast screen without the massive long-term height of the ‘Green Giant’.
Slower, more compact cultivars, such as ‘Emerald Green’ (Thuja occidentalis ‘Smaragd’) and ‘Nigra,’ offer a more restrained annual growth rate. ‘Emerald Green’ often gains between six and twelve inches per year once established, while the dark-foliaged ‘Nigra’ typically adds six to eight inches annually. This slower pace results in a denser, narrower form that requires less maintenance over time.
Environmental Influences on Growth Speed
While genetics set the maximum potential, environmental variables determine if an arborvitae reaches its optimal annual growth rate. Soil quality is a leading factor, as arborvitae require well-drained, loamy soil to prevent root issues. Poor drainage or compacted soil restricts oxygen supply to the roots, potentially causing root rot and severely stunting growth.
The tree’s ability to absorb nutrients is directly tied to the soil’s pH level, with a preferred range of 6.5 to 8.0. If the pH is too far outside this range, essential elements become chemically locked in the soil, preventing uptake and leading to deficiencies that slow growth.
Sunlight exposure is another important component, as arborvitae perform best in full sun, requiring a minimum of six hours of direct light daily. Trees planted in excessive shade will often exhibit thinner, less dense foliage and a reduced vertical growth rate as they struggle to produce sufficient energy through photosynthesis.
Temperature and water availability also dictate the timing and extent of annual growth. Arborvitae do most of their growing in the cooler, moist conditions of spring and early summer, while prolonged periods of heat or drought stress the plant, limiting shoot elongation.
Growth Dynamics: Establishment and Maturation
The annual growth rate is not constant throughout the tree’s lifespan but follows a predictable pattern related to its age and maturity. Immediately following planting, the tree enters the establishment phase, typically lasting one to three years, allocating energy toward developing a strong, extensive root system.
Above-ground growth is significantly minimized during this establishment period. For example, a young ‘Green Giant’ that should eventually grow five feet in a year might only add six to eighteen inches in its first season, as this initial focus on root biomass supports the accelerated growth that will follow.
Once the root system is well-established, the arborvitae enters its juvenile or accelerated growth phase, where it achieves the maximum annual growth rates associated with its cultivar. Eventually, as the tree approaches its genetically determined maximum height, it shifts into the maturation phase, and the annual growth rate naturally begins to slow. The plant’s energy is redirected away from vertical growth toward maintaining its existing canopy and increasing its trunk girth and lateral spread.