Evergreen trees and shrubs retain foliage year-round, distinguishing them from deciduous plants. This unique growth pattern necessitates a distinct approach to pruning. Understanding how evergreens grow and heal is paramount, as incorrect cuts can leave permanent bare patches that the plant cannot easily repair. Pruning is a management tool used to maintain health, control size, and guide development. Since evergreens lack the abundance of latent or dormant buds found on the old wood of many deciduous species, mistakes can be irreversible.
Pruning Timing and Essential Preparation
The optimal timing for pruning most evergreens falls into two main periods, depending on the species and desired outcome. The most common time is late winter or very early spring, just before new growth begins. Pruning during this dormant period minimizes stress and ensures vigorous spring growth quickly conceals the cuts, aiding in a clean aesthetic.
An alternative time for maintenance and shaping is the semi-dormant period in mid-summer, after the initial flush of spring growth has matured. This timing is useful for formal hedges or topiaries, allowing for a second shaping cut without stimulating tender new growth susceptible to winter damage. Flowering broadleaf evergreens, such as rhododendrons, are an exception; they should be pruned immediately after blooming to protect next year’s flower buds.
Before making any cuts, gather the proper tools for a clean, efficient job that promotes plant health. Hand pruners are suitable for small twigs up to a half-inch in diameter. Loppers provide leverage for branches up to an inch and a half, and a pruning saw should be used for any larger limbs. Ensure cuts are made cleanly without tearing the bark.
Sanitation of cutting tools significantly reduces the risk of transmitting diseases between plants. A solution of 70% isopropyl rubbing alcohol is an excellent disinfectant because it is effective against most pathogens and does not cause metal tools to rust. Wiping or spraying the blades with the alcohol solution between plants, especially after cutting diseased wood, is sufficient. Bleach solutions (one part bleach to nine parts water) can also be used, but they require rinsing to prevent metal corrosion.
Understanding Evergreen Growth Habits
The fundamental difference in pruning evergreens lies in their ability to generate new growth from old wood. Most conifers (pines, spruces, and firs) grow from pre-formed buds at the tips of branches and shoots. They have very few dormant buds hidden beneath the bark on older, leafless wood. Cutting back past the existing green needles into this “dead zone” typically results in a permanent stub that will not regenerate foliage.
This growth pattern is influenced by apical dominance, where the hormone auxin, produced at the terminal bud, inhibits the growth of lower side shoots. This mechanism encourages the plant to grow upward, creating the characteristic conical shape of many conifers. When the apical leader is removed or damaged, the hormonal balance shifts, stimulating lateral buds below the cut to grow, leading to a bushier, denser appearance.
Broadleaf evergreens (yews and some holly) and random-branched conifers (arborvitae and juniper) exhibit a different habit. These species often have a greater capacity to produce new growth from latent buds along the stem. This allows them to tolerate harder pruning than whorled-branching species like pine. However, extreme cuts into wood that has been bare for several seasons should still be avoided, as regeneration diminishes with the wood’s age.
The presence of a strong central leader is a defining trait for many evergreens, and its maintenance is important for structural integrity. If the main leader is lost or damaged, the tree often attempts to replace it by turning adjacent lateral branches upward. Gardeners can assist this by selecting the strongest lateral shoot and splinting it vertically to serve as the new leader, ensuring the tree retains its natural growth form.
Specific Techniques for Shaping and Health
All pruning should begin with maintenance cuts to improve the plant’s health. This involves removing any wood that is dead, diseased, or damaged (D-D-D), which can be done at any time of year. Dead wood should be cut back to its point of origin or to a lateral branch junction where living tissue is present. When removing a diseased branch, cuts must be made well into the healthy wood below the infection point, and tools must be immediately disinfected.
For pines and firs, managing size and density is achieved through candle pruning. The “candle” is the new, soft, upright shoot that emerges in the spring before the needles fully expand. By pinching or cutting this new growth back by one-half to two-thirds of its length, the overall yearly extension is reduced. The remaining portion sets buds that create a denser branch structure the following year. This technique is species-specific and must be performed within a narrow window in the spring.
When shaping, the choice between shearing and selective cuts depends on the desired outcome. Shearing uses hedge trimmers to create a formal, geometric shape, typically for hedges and topiary. However, shearing only cuts the outermost foliage. This can cause the interior to become shaded and develop an unproductive “dead zone” that cannot recover if cut back too far.
Selective pruning, or “heading back,” involves cutting individual branches back to a healthy side shoot or bud deeper within the canopy. This method maintains the evergreen’s natural shape while encouraging denser growth throughout the branch structure. It is the preferred method for overall size reduction. To reduce the size of a mature evergreen, never remove more than 25 to 30% of the plant’s total foliage in a single season. This conservative approach prevents stress and ensures the plant retains enough photosynthetic capacity to recover.