The common Arborvitae, a species of Thuja, is a popular evergreen choice used for privacy screening and hedges due to its dense, fast-growing nature. Homeowners frequently face the dilemma of managing the height of these columnar trees as they rapidly outgrow their intended space. The immediate, but incorrect, impulse is often to simply cut off the top, a practice known as “topping.” While the desire to control a tree’s size is understandable, the answer to whether you can safely top an Arborvitae is a definitive no. The reasons are rooted deeply in the tree’s biology, and this destructive pruning method permanently compromises both the plant’s health and its appearance.
Why Topping Destroys Arborvitae Health and Appearance
Topping is fundamentally damaging because this conifer lacks the biological mechanism to recover from such a severe cut. Unlike deciduous trees, Thuja species do not have latent or dormant buds in the inner, brown, non-photosynthetic sections of their branches. When the top is sliced off, the cut exposes old wood incapable of generating new green foliage. This results in a permanent, flat, brown scar that will never “green up” again.
The drastic removal of the tree’s crown severely stresses the organism by eliminating a large portion of its photosynthetic capacity. Needles create the energy the plant needs to survive, and removing them forces the tree to deplete its stored reserves. The tree’s survival response is to rapidly produce numerous thin, upright shoots, often called watersprouts, immediately below the cut. These shoots are poorly anchored to the main stem, creating a weak attachment point highly susceptible to breakage during strong winds or heavy snow.
A topped tree is left with a large, open wound that it cannot effectively seal off, providing an easy entry point for decay organisms, insects, and fungal pathogens. The interior wood of the trunk, exposed to moisture and air, begins to rot, which compromises the structural integrity of the plant. The aesthetic failure is irreversible; the tree is left with an unnatural, disfigured, flat-top appearance that ruins its natural pyramidal or conical form. The weak watersprout growth requires continuous pruning and can quickly grow back to the tree’s original height, defeating the initial goal of size reduction.
Proper Techniques for Height Reduction
When Arborvitae height must be reduced, the correct technique involves reduction cuts focused on maintaining the plant’s natural structure. Instead of an indiscriminate horizontal cut, the height is reduced by selectively cutting the main leader back to a healthy, strong lateral branch growing in the desired direction. This lateral branch must be at least one-third the diameter of the removed leader to successfully take over the role of the new terminal leader.
This technique, sometimes called the “drop-crotch” method, allows the tree to seal the smaller wound more efficiently and directs growth energy into the new leader. The goal is to make these cuts deep within the foliage canopy so the remaining green material hides the pruning wound. This method ensures the cut is not noticeable and preserves the plant’s characteristic shape. The key principle is to prune only the new, green growth and never cut back into the brown, bare wood.
Long-Term Size Management and Remediation
Controlling the width of an Arborvitae is generally a simpler task than height reduction and is achieved by lightly shearing the sides, cutting only the new, green tips to encourage dense, full growth. It is crucial to ensure that you do not cut beyond the green foliage layer. For major structural pruning and height reduction, the ideal time to prune is during late winter or early spring, just before the new growth cycle begins. Pruning at this time allows the tree to use its stored energy to quickly compartmentalize the wound and begin new growth.
If an Arborvitae has already been topped, remediation is a long and uncertain process. Since the cut surface will never regrow, the damaged tree can only be salvaged by training a new leader to take over the vertical growth. This involves selecting one of the strongest, most upright watersprouts near the cut and staking it vertically to replace the lost leader. This process can take several seasons, and the middle section of the tree may remain thin until the new growth fills the gap. If the topping was severe, or if the tree shows signs of decay or structural failure, the most practical solution may be complete removal and replacement with a smaller, appropriately sized cultivar.