The Thuja occidentalis ‘Smaragd’, commonly known as the Emerald Green Arborvitae, is a popular evergreen known for its narrow, columnar structure and vibrant, year-round foliage. Its natural growth habit makes it a favored choice for creating privacy screens and hedges, even in compact landscapes.
The height of an Emerald Green Arborvitae can be successfully managed to suit your landscape’s scale. This control requires a consistent, proactive maintenance strategy, not a single, dramatic cut. Understanding the plant’s biology is the first step toward keeping it at a desired, shorter stature without compromising its dense, attractive appearance.
Understanding the Emerald Green’s Growth Pattern
The Emerald Green Arborvitae is a semi-dwarf cultivar that is genetically programmed to grow into a compact, narrowly pyramidal shape. Its growth is dominated by a strong central leader, which dictates its vertical reach. If left unpruned, this cultivar commonly grows to heights between 12 and 15 feet, though some specimens may reach 20 feet in ideal conditions.
The upward growth rate is moderate compared to other evergreens, typically adding about 6 to 12 inches of height per year. This steady, predictable increase occurs primarily at the tips of the branches and the top of the main leader. Consistent annual growth means that height control must be an ongoing commitment rather than a one-time event.
The narrow form is maintained by a slower outward growth rate, usually increasing by only 1 to 2 inches in width annually. This naturally compact habit suits the Emerald Green well for smaller yards and tight hedge rows. The foliage consists of dense, scale-like leaves that maintain their deep green color through all seasons, contributing to its solid, screen-like look.
Proper Techniques for Maintaining Shorter Height
Controlling upward growth is achieved by heading back the terminal leader. This technique involves selectively removing the active growth tips to stop vertical extension once the plant approaches the preferred height. The best time to perform this major cut is during the dormant season in late winter or early spring, just before new growth begins.
To establish a shorter, fixed height, identify and remove the main leader branch. Make a clean cut with sharp hand pruners, removing the top portion just above an outward-facing lateral branch or bud. This cut redirects the plant’s growth hormones, reducing the vertical urge and encouraging remaining lateral branches to become fuller and denser.
Subsequent annual maintenance involves removing only the newest growth from the top to maintain the established line. Do not remove more than 20% of the plant’s total height in any single pruning session, as this can severely stress the plant. Consistent, light trims are better for the plant’s health and appearance than attempting a large reduction all at once.
For optimal density, light trimming can also be performed in mid-summer after the initial flush of spring growth has matured. This summer trim should only involve shearing the tips of the new growth. This encourages the outer foliage to branch out and form a tight, uniform surface, creating the desirable, dense appearance of a manicured hedge.
When trimming the sides, ensure the base of the arborvitae remains slightly wider than the top, creating a slight pyramidal shape. This allows sunlight to reach the lower branches, preventing them from thinning out and turning brown. If the top is wider, it shades the lower growth, leading to sparse foliage near the bottom.
The Dangers of Cutting Into Old Wood
One biological limitation to understand when pruning an Emerald Green Arborvitae is its inability to regenerate from old wood. Unlike many deciduous shrubs that can sprout new growth from interior tissue, Thuja species lack dormant buds on their older, inner branches.
Old wood is the brown, woody portion of the branch that no longer has green, scale-like needles attached. If a pruning cut penetrates this area, the resulting gap will not fill back in with new foliage. The remaining brown stub will be permanently exposed, leading to unsightly, non-recoverable brown patches.
Because of this biological constraint, severe size reduction of an overgrown arborvitae is risky. If a plant has significantly exceeded its intended height, cutting it back drastically will result in a permanent, bare look that compromises its aesthetic appeal. For successful height maintenance, always cut back only into the green, leafy portion of the plant.