Thuja trees, commonly known as Arborvitae, are highly valued for their dense, evergreen foliage and their ability to quickly form privacy screens or hedges. These conifers are popular choices for homeowners looking to establish a barrier or background planting with minimal delay. Understanding the specific growth characteristics of different Thuja varieties is necessary for setting realistic expectations and achieving desired landscaping goals.
Comparing Growth Rates of Popular Thuja Cultivars
The term “Thuja” encompasses several species and numerous cultivars, each with a distinct annual growth rate. Growth rates are measured after the tree spends its first year or two establishing a strong root system, often called the “sleep” period. This initial phase is followed by the tree’s most vigorous growth, which determines how quickly a hedge or screen will mature.
The most celebrated fast-growing Thuja is the ‘Green Giant’ (\(Thuja\) ‘Green Giant’). This hybrid is known for its impressive performance, adding between 3 and 5 feet of height each year under optimal conditions. Its rapid growth makes it one of the quickest options for creating a tall, dense screen.
In contrast, the ‘Smaragd’ cultivar (\(Thuja\) \(occidentalis\) ‘Smaragd’), often called Emerald Green Arborvitae, is a much slower grower. This variety is prized for its narrow, columnar form and vibrant green color that holds well through winter. The ‘Smaragd’ typically grows at a rate of only 6 to 12 inches per year. This slower pace is often preferred for those seeking a dense, manageable hedge that requires minimal pruning. Other varieties derived from the native American Arborvitae (\(Thuja\) \(occidentalis\)) exhibit a moderate growth rate, typically adding 12 to 24 inches annually.
Environmental Factors Influencing Growth Speed
The growth rates cited for any Thuja cultivar represent the maximum potential, achieved only when environmental conditions are favorable. Sunlight is a major determinant of growth speed and foliage density. Thuja varieties perform best with at least six hours of direct sunlight per day (full sun). While they can tolerate partial shade, insufficient light will dramatically slow the growth rate and lead to thinner foliage.
Soil quality and drainage also play a significant role in maximizing growth potential. These conifers thrive in moist, fertile, well-drained loamy soils. Poorly drained or compacted soils can severely impede root growth and nutrient uptake. Conversely, planting in soil that is too dry or on an exposed, windy site stresses the tree, resulting in a reduced growth rate.
The local climate and the tree’s hardiness zone must be suitable for sustained, vigorous growth. The length of the growing season directly affects how much growth Thuja trees can achieve in a year. Planting outside the recommended hardiness zone can lead to winter injury or heat stress. Both conditions divert energy away from height and density gains.
Practical Steps to Maximize Thuja Growth
To ensure Thuja trees meet or exceed expected growth rates, active maintenance is required, particularly during the establishment phase. Consistent and deep watering is effective for encouraging rapid growth in the first few years after planting. Drought stress can halt growth completely, so provide about one inch of water per week, especially during dry spells.
The use of fertilizer provides the necessary nutrient boost to support vigorous growth. Applying a balanced, slow-release fertilizer in early spring helps sustain the tree’s energy needs throughout the growing season. Avoid over-fertilizing, which can cause root damage, and use products specifically formulated for evergreens.
Proper planting technique ensures quick root establishment, which is foundational to future growth. The planting hole should be dug twice as wide as the root ball, but only as deep as its height, preventing the tree from settling too low. Applying a 3- to 4-inch layer of organic mulch around the base helps retain soil moisture and regulate temperature. Keep the mulch a few inches away from the trunk to prevent rot.
While Thuja trees generally require minimal pruning, strategic light trimming promotes denser growth, desirable for a privacy screen. Pruning should be done in late winter or early spring before new growth begins. Avoid heavy shearing, as it can temporarily slow height gain and expose the interior of the tree.