The Emerald Green Arborvitae, scientifically known as Thuja occidentalis ‘Emerald Green’, is a popular, low-maintenance evergreen widely used in landscaping for its dense, narrow, and naturally pyramidal form. While these trees can grow without intervention, proper pruning is necessary to maintain their compact shape, prevent snow damage, and encourage thick, lush foliage.
Optimal Timing and Necessary Tools
The most effective time for significant pruning is in late winter or early spring, just before the new seasonal growth begins. Pruning during this dormant period minimizes stress on the tree and allows it to direct energy toward recovery and vigorous new growth once the weather warms. Avoiding late-season cuts, particularly in late summer or fall, is important because the resulting soft new growth will not have time to harden before cold weather and can suffer from winter burn.
Lighter shaping or minor touch-ups can be performed in early summer after the initial flush of growth has matured. To execute the cuts precisely, you will need a few sharp, clean tools to prevent the introduction of disease and ensure quick healing. For selective cuts on smaller, individual branches, use bypass hand pruners, which create a clean, scissor-like cut.
Hedge shears can be used sparingly for light surface shearing to maintain a uniform appearance on a hedge line, but they should not be the primary tool for deep cuts. For removing thicker, damaged, or dead branches, loppers offer the necessary leverage. Always ensure all tools are sanitized before use to protect the tree’s health.
Pruning Techniques for Shape and Density
Emerald Green Arborvitae responds best to selective, light pruning that targets the tips of the branches, rather than aggressive shearing. The primary goal of maintenance pruning is to stimulate lateral branching, which creates a denser, more private screen or specimen. By lightly trimming the outer growth, you activate dormant buds closer to the surface, encouraging them to sprout. When making a cut, always locate a lateral bud or a small side branch and trim just above it. This technique directs the plant’s energy to the remaining external growth, promoting a bushier habit.
It is paramount to preserve the tree’s natural pyramidal structure, ensuring the base remains slightly wider than the top. This wider base allows sunlight to reach the lower branches, preventing them from thinning out and turning brown due to lack of light penetration. For overall tree health, you should never remove more than one-third of the total foliage in a single pruning session.
Light surface shearing can be used to achieve a formal, uniform hedge line, but this should be minimal and focused only on the newest growth. Consistent, light annual pruning is the most effective approach for long-term shape retention and health.
Addressing Specific Growth Issues
Corrective pruning is sometimes necessary to address structural problems or damage that occurs outside of routine shaping. Any dead, damaged, or diseased branches should be removed immediately upon detection, regardless of the season, by cutting back to healthy wood or to the main trunk. This removal is particularly important after heavy snow or ice events that can weigh down and break the tree’s branches.
A common issue in mature arborvitae is excessive height, which can be corrected by cutting the central leader, the main vertical stem. To reduce height, the leader should be trimmed down to a strong, vigorous lateral branch that can take over as the new terminal point. This cut will stop upward growth, causing the tree to focus its energy on widening and becoming denser.
A strict rule for pruning this species involves recognizing the “dead zone,” which is the interior of the tree where sunlight does not reach, causing the foliage to turn brown and shed. Arborvitae, unlike some other evergreens, will not regenerate green growth from this old, non-leafy wood. Cutting into the dead zone will create a permanent, brown, and unsightly hole in the foliage that will not fill in.
Post-Pruning Care and Common Errors
After pruning, especially following a more substantial cut, the arborvitae will benefit from a deep, thorough watering. Ensuring the root zone is adequately hydrated helps the tree recover from the stress of pruning and supports the initiation of new growth. Avoid applying a nitrogen-heavy fertilizer immediately after pruning, as this can encourage a rush of soft growth that is more susceptible to pests and environmental damage. If you choose to fertilize to boost general health, use a balanced, slow-release product in early spring or late fall, following the manufacturer’s recommendations.
Applying a fresh layer of mulch around the base of the tree, keeping it a few inches away from the trunk, helps to conserve soil moisture and regulate temperature fluctuations. Mulch also provides a neat, finished appearance to the planting area.
Several common errors can compromise the health and appearance of the Emerald Green Arborvitae.
- Cutting too deep into the inner dead zone, resulting in bare spots that will never recover.
- Removing too much green foliage at once, especially exceeding the recommended one-third limit, which can shock the tree and cause browning.
- Pruning too late in the growing season, such as in the fall, because the tender new shoots stimulated by the cut will be damaged by the winter cold.
- Consistently shearing the sides vertically instead of maintaining a wider base, which causes the lower branches to be shaded out, leading to thinning at the bottom.