The Emerald Green Arborvitae (Thuja occidentalis ‘Smaragd’) is a popular evergreen favored for its naturally narrow, columnar shape and its ability to maintain dense, vibrant green foliage throughout the year. Understanding its predictable pattern of development, or “growth chart,” is necessary for effective long-term landscape planning, especially when establishing privacy screens or formal hedges.
Understanding the Standard Growth Trajectory
The growth trajectory of the Emerald Green Arborvitae is intermediate, significantly slower than many other screening evergreens. Under optimal conditions, the plant typically exhibits an annual vertical growth rate of six to twelve inches once established. This steady pace allows the ‘Smaragd’ cultivar to maintain its tight, pyramidal form without frequent shearing.
The plant dedicates its early years to root establishment, often resulting in a slightly faster rate of up to one or two feet annually for the first few seasons before settling into its long-term pattern. This initial burst prepares the tree to support its mature size. Mature height usually falls within twelve to fifteen feet, though some specimens may reach slightly taller dimensions in highly favorable environments.
The horizontal spread remains compact, generally maxing out at three to four feet wide, making it suitable for narrow spaces and property lines. The time required to reach full mature height and width is approximately ten to fifteen years, which sets realistic expectations for privacy screen development.
The slow growth rate contributes to the dense internal structure of the foliage, which is why the cultivar is prized for hedges. This density ensures year-round opacity, unlike faster-growing varieties that can become thin or open over time. Understanding these standard parameters is the foundation for predicting performance, but actual size and speed are modulated by external factors.
Environmental Factors Shaping Growth
The growth rate often deviates from the standard trajectory due to various environmental influences, with sunlight being a primary modulator. Emerald Green Arborvitae thrives best when it receives a minimum of six hours of direct sun daily, promoting the densest foliage and highest growth velocity. Placing the plant in partial shade can lead to sparser branching and a slower accumulation of biomass.
Soil conditions play a fundamental role in sustained health and vigor, particularly the balance between moisture retention and drainage. The plant prefers a rich, well-drained loam but tolerates a range of soil types, including some clay and sand. The soil pH preference is neutral to slightly alkaline (6.0 to 8.0).
Poor drainage is a major impediment to growth, as it quickly leads to root rot (Phytophthora species), stunting the plant by compromising its ability to absorb water and nutrients. Consistent water availability is important during the first few years as the root system establishes itself. While mature arborvitae are moderately drought-tolerant, prolonged dry periods can slow the growth rate substantially and may cause foliar browning or tip burn.
The appropriate climate also dictates the tree’s potential, with the Emerald Green Arborvitae performing optimally across USDA Hardiness Zones 3 through 7. Trees planted at the cooler end of this range may experience slightly reduced growth due to a shorter growing season. Conversely, in regions with intense summer heat, afternoon shade can be beneficial, preventing stress that leads to a temporary pause in development.
Maintenance Practices for Size Management
While genetic programming determines the ultimate size and potential rate, human intervention can manage the tree’s health and influence its final dimensions. Correct initial spacing directly impacts the width and overall health of the arborvitae row. Planting trees three to five feet apart provides adequate room for air circulation, which helps prevent fungal issues and allows each plant to reach its full mature spread without crowding.
Pruning serves primarily to maintain density and manage the vertical dimension. Light tip-pruning or shearing in the early spring, just before the flush of new growth, encourages the plant to branch out, resulting in a thicker, fuller screen. Avoid heavy, corrective pruning into the old, leafless wood, as arborvitae do not readily regenerate growth from these interior sections.
Fertilizer application can maximize the growth rate, particularly in younger trees or those planted in poor soil. A balanced, slow-release evergreen fertilizer applied in early spring provides the necessary nitrogen for vigorous shoot growth. However, once established, excessive fertilization is often counterproductive, potentially leading to weak, unnatural growth or fertilizer burn.
Ensuring the correct planting depth is a primary maintenance practice for long-term, sustained growth. The root flare, the point where the trunk widens at the base, must be positioned at or slightly above the surrounding soil level. Planting the tree too deeply is a common error that suffocates the roots and stunts the plant’s development.