Pruning evergreen shrubs requires understanding the plant’s biology to maintain both health and desired form. Evergreens are defined by their year-round foliage, encompassing needle-leafed conifers like pines and broadleaf evergreens such as boxwoods and hollies. The primary objectives of trimming are managing the plant’s size, improving its structure, and enhancing its aesthetic appearance. Proper technique prevents damage, encourages dense growth, and ensures the shrub remains a healthy, attractive specimen.
Essential Tools and Timing
Successful evergreen pruning requires the right equipment and a well-timed approach. Bypass hand pruners provide the cleanest cut for small branches up to half an inch in diameter, while loppers are suitable for thicker branches up to two inches. Hedge shears, manual or powered, are used specifically for formal shaping and shearing. Disinfecting all cutting tools with a solution of one part bleach to three parts water before and after use prevents the transmission of plant pathogens between shrubs.
The most opportune time to prune most evergreens is in late winter or early spring, just before the first flush of new growth begins. Pruning during this period allows the subsequent growth to quickly conceal the cuts, maintaining a natural appearance. Alternatively, a second light pruning can be done in mid-summer after the initial rapid growth has matured. Avoiding heavy pruning in late summer or fall is crucial because new, tender growth stimulated by the cuts will not have time to harden before winter frosts, making it vulnerable to cold damage and dieback.
General Shaping and Reduction Techniques
Pruning involves two primary methods: shearing for formal shapes and selective thinning for a more natural look. Shearing utilizes hedge trimmers to cut the outer tips of branches back to a uniform plane, stimulating dense growth on the shrub’s surface. When shearing a hedge, taper the shape so the base remains slightly wider than the top. This conical shape ensures sunlight reaches the lower branches, preventing the bottom foliage from thinning out and turning brown.
Selective thinning, also known as hand pruning, is preferred for maintaining the natural habit of individual shrubs. This technique involves removing entire branches or cutting them back to a healthy side branch, a lateral bud, or the main trunk. Cutting back to a side branch is called a reduction cut, which effectively shortens the branch while directing new growth outward. Thinning cuts increase air circulation within the canopy and allow light to penetrate the interior foliage, keeping the shrub dense and reducing disease pressure.
To safely reduce the overall size of an overgrown evergreen, never remove more than one-third of the total foliage in a single season. When attempting size reduction, cut the longest branches back to a point where they meet a healthy, younger side branch or a junction. This careful method avoids leaving large, bare sections of wood, which many evergreens cannot regenerate foliage from. Consistent annual maintenance through thinning and light heading cuts prevents the need for drastic size reduction later on.
Structural Differences in Evergreen Pruning
Evergreens fall into two broad structural categories that dictate how they respond to being cut. Species like pine, spruce, and fir are known as terminal bud growers, meaning they only produce new growth from the terminal buds located at the tips of their branches. These plants cannot generate new shoots from old, bare wood.
Pruning terminal bud growers requires a technique called “candling,” which involves pinching or cutting the soft, newly emerged growth—the “candles”—by about half their length in the spring. This encourages the remaining bud tissue to branch out, resulting in denser growth. Because these species lack latent buds on older wood, cutting back past the current year’s needles into a bare section of a branch creates a permanent dead spot that will never fill in with foliage.
In contrast, evergreens such as yews, boxwoods, and arborvitae are classified as lateral bud growers and have latent buds beneath their bark. This structural difference allows them to tolerate much more severe pruning, including being cut back into older wood that appears bare. Latent buds are activated by the removal of the outer foliage, prompting the plant to generate new shoots and readily fill in gaps. This makes lateral bud growers excellent choices for formal hedges and topiary, as they can be heavily sheared and reduced in size without permanent damage.