Evergreen refers to a group of plants that retain their foliage during winter. Most evergreens have a strong central branch leader, which requires little pruning except to control plant height, increase the density of branching, or to shear into special shapes.
Proper identification and growth habits are necessary before pruning or the natural shape and beauty of a plant can be destroyed. Evergreens can be grouped on the basis of whether they have whorled branches (pines, spruces, firs, and Douglas-fir) or random-branching patterns (yew, arborvitae, hemlock, cedar, and juniper). New growth extends from buds that were formed the previous year on the tips of twigs. However, a few random-branched species are capable of generating new growth on both old and new wood portions of the branch.
Prune all evergreens, except pine, before new growth starts in the spring or during the semidormant period in mid-summer. When pruning, follow the general branching pattern to maintain the natural shape. Remove dead, diseased, or broken branches anytime. When shearing, begin in late spring or early summer when new growth begins. This allows cuts to heal and new buds to form for next year. In most cases, selective pruning (one branch at a time) is better than shearing. Shearing creates a formal, geometric shape that looks out of place in a natural landscape and becomes more difficult to maintain as the plant increases in size. (Pruning paints are not necessary since pitch quickly seals the pruning wound.)
Occasionally, an evergreen may lose its leader. Sometimes a new leader develops from a latent (dormant) bud, or one of the uppermost branches will dominate and become the new leader. If no leader develops naturally, tie one of the topmost branches upright, training it to become the new leader. Shorten surrounding lateral branches to reduce competition.
Pines (Pinus) Pine needles are arranged in clusters or bundles, which are fastened to a twig in a sheath. The number of needles in a cluster varies from species to species, but usually they are in bundles of two, three, or five. Most pines produce their buds on the terminal tips of their shoots and not along the stems. This results in one flush of growth per year. New shoots are called candles.
- Prune pines in the spring as new growth emerges.
- To produce a compact, uniform plant or to maintain a plant shape, pinch one-third to one-half of each candle when it expands in the spring. Do not prune back into woody stems; new growth will not develop from these areas. Shearing is not recommended.
- When older pines are overgrown, the only option usually is to remove an entire branch.
Spruces have individual, angled needles with brown pegs at the base of each needle. The pegs remain on the twig after the needles drop, resulting in a rough twig. Buds are scattered along the twigs of the newest growth. Cones are long and pendulous. Although spruces need very little pruning, bottom branches may die with age and can be removed.
- For a formal shape, prune new growth in the spring. Shear in late spring, after new growth has expanded.
- To reduce the size of a branch, cut back to a lateral branch or a visible dormant bud. This can be done at any time.
- To repair a broken leader, cut off the broken branch and tie one of the shorter side shoots upright onto a splint, training it to become the new leader. Remove the tie after one year. If two leaders develop, remove the weaker one.
- Prune firs as you would a spruce. Douglas-Fir (Pseudotsuga)
Although not a true fir, the overall form is similar to spruces and firs. Douglas-fir has flat needles and smooth twigs on pendulous branches. Cones have distinctive bracts extending beyond the scales.
- Prune as you would a spruce.
Arborvitae (Thuja) The needles of arborvitae are flat, frond-like fans. Cones are distinct, half-inch clusters. Arborvitae comes in many different forms and sizes that should be maintained when pruning. Arborvitae will withstand heavy pruning and shearing because new branches develop from concealed buds in the branch crotches. Prune in early spring or mid-summer.
- When heavy pruning is necessary, prune before new growth begins in early spring so that new growth conceals pruning cuts.
- To lower the height (no more than 20 percent) of a plant, cut back to a lower branch crotch, making cuts only into live wood. To regain the natural shape of the plant, balance lower limbs by lightly pruning branch tips.
- Older arborvitae growing in shade will develop a dead zone that is incapable of regenerating new growth. Do not prune into this area.
- Oriental arborvitae (Thuja orientalis) is slow growing and responds best to shearing new growth only.
This diverse group of plants includes spreading, upright, pyramidal, and creeping habits. Junipers have two types of needles, one scalelike and the other prickly and sharp. Both types are often seen on the same plant. Fruit is a distinct, light blue, berry-like cone. All junipers develop a dead zone in the center of the plant because of insufficient light. New growth will not develop from this area unless green needles remain. Severe pruning is not recommended.
- To correct the shape, prune before new growth starts in the spring; lightly prune side branches to reduce their size and to bring the plant back into scale.
- Prune spreading and creeping junipers by selectively cutting back to vigorous, lateral side branches. Do not shear in a formal manner.
- Overgrown specimens can be lowered up to 20 percent, but cuts must be above the dead zone.
- When shearing junipers, care should be taken to leave some new growth on the plant to avoid pruning back into the dead zone. Shearing should take place in the spring when plants are actively growing.
Needles are glossy, dark green, and arranged spirally in pairs along erect stems. Fruit is a fleshy, red berry. Yews range from spreading ground covers to various-sized trees and shrubs. Yews are slow-growing, long-lived plants, which produce two flushes of growth per year. New growth will develop on old wood, making yews very tolerant of heavy pruning or shearing.
- To maintain size, prune in late winter or early spring, before new growth begins. Prune again in mid-June.
- Annual shearing should be done after new growth has expanded. Follow-up shearing should continue throughout the growing season. To avoid stimulating new growth late in the season (thus preventing winter injury), do not shear yews after August.
On hemlocks, small, flat, dark greenneedles are arranged spirally around the stem. Cones are small and pendulous. Hemlock grows as a tall tree, but can be pruned or sheared as a hedge.
- Prune as you would a yew.