Cedar bushes, commonly known as Arborvitae or Thuja, are favored landscape plants prized for their dense, evergreen foliage and ability to form natural privacy screens. Proper, consistent trimming is necessary to maintain their desired shape and ensure the health of the plant. Unlike many deciduous shrubs, cedar bushes require a specific approach to pruning, as their internal structure makes them extremely sensitive to deep cuts. Following specific physiological rules is the only way to keep them looking lush and green without causing permanent damage.
Understanding Cedar Growth Habits
The unique physiology of the cedar bush dictates a cautious trimming strategy. Cedar foliage is densest at the surface, which blocks sunlight from penetrating the interior. This lack of light causes older growth and inner branches to turn brown, creating a “dead zone” of leafless wood near the trunk.
The plant can only generate new growth from the green, photosynthetic tissue on the outer layer of the branches. If a cut is made past this green layer into the brown, leafless wood, the branch will not regenerate new foliage. Cedars cannot regrow from old wood, which is the most important rule to remember when trimming. Consistent light pruning encourages the development of more lateral shoots near the surface, helping the bush grow thicker and maintain a uniform appearance.
Optimal Timing and Necessary Tools
The ideal window for routine maintenance trimming is generally from late spring through mid-summer, after the initial flush of new growth has matured. Trimming during this period allows the cedar to heal and produce secondary growth before the onset of cold weather. Pruning too late in the season, such as in the fall, can stimulate tender new growth that may be damaged by winter frost, weakening the plant.
Sharp, clean tools are necessary to make precise cuts that heal quickly and minimize stress on the plant. Handheld bypass pruners are suitable for removing small, individual branches or light tip-trimming. Hedge shears, whether manual or powered, are used for shaping and removing large amounts of new growth quickly, especially for formal hedges. For thicker, established branches, loppers or a small pruning saw may be needed, but these should be used sparingly and only on green wood.
Essential Trimming Techniques
The fundamental rule for maintaining healthy cedar bushes is the “one-third rule,” which dictates that you should remove no more than one-third of the current year’s new growth during any single pruning session. This light trimming strategy ensures the plant retains enough foliage to produce food and remain vigorous. The new growth is typically lighter green than the older foliage, making it easy to identify the appropriate cutting zone.
When shaping the bush, ensure the base remains wider than the top, creating a slight A-frame or pyramidal shape. This contour allows sunlight to reach the lower branches, preventing them from thinning out due to insufficient light. If the top is wider, it casts shade on the bottom, leading to a sparse, brown lower section over time.
All trimming cuts must be kept within the green foliage and should never penetrate the brown, leafless wood in the center. Cutting into the dead zone results in permanent bare spots, as cedars lack the latent buds needed to sprout new growth from old wood. To achieve a clean, manicured look, step back frequently while trimming to assess the overall shape and symmetry, making small, incremental adjustments rather than large cuts.
For formal hedges, use a straight edge or taut string line to guide cuts and ensure a consistent height. For a more natural look, use selective pruning where you cut back individual branches to a lateral side branch or a bud within the green zone. Regular, light shearing of the tips during the growing season encourages the dense, full appearance characteristic of a healthy cedar hedge.
Addressing Overgrown Bushes
Dealing with severely overgrown cedar bushes presents a distinct challenge because of their inability to regenerate from old wood. Unlike deciduous plants that can be cut back aggressively, a cedar cut hard into the dead zone will likely not recover and may be permanently disfigured. If a cedar has become far too tall or wide, replacement is often the most effective option if a major size reduction is necessary.
If the bush is only moderately overgrown, the only viable method for size reduction involves a gradual process over two to three seasons. The goal is to reduce the size without cutting past the green growth. In the first year, remove only the maximum one-third of the new growth to expose slightly more inner green foliage to light.
Repeat this light pruning in subsequent years, allowing the exposed inner foliage to become denser before cutting back further. This slow, staggered approach encourages new growth to form closer to the trunk, which can eventually fill in the space and mask the reduction. Any dead or diseased branches should be removed entirely, cutting them back to the trunk or to a point where they join healthy, green wood.