|B. Rosie Lerner|
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Evergreens require a bit different manner of pruning than other landscape plants. Although a plant is not likely to die from improper pruning, it is important to note that most evergreens cannot replace lost growth the way that deciduous plants can. So while other landscape plants might be able to outgrow an errant pruning job, evergreens can suffer permanent disfigurement.
Individual plants should be assessed for pruning needs. Evergreens that have been sheared into formal or artificial shapes require frequent pruning. However, many evergreens may rarely need pruning.
As with other plants, the first objective of pruning is to remove any dead or damaged wood. Prune back to a branch that is pointed in the direction that you want the new growth to go, always making sure to cut back into healthy wood.
The term evergreen is used to refer to many different kinds of plants and all are not pruned in the same manner. Trees such as spruce and pine have very different pruning requirements than shrubs such as yew and juniper.
Some evergreen shrubs should be thinned occasionally to prevent lower branches from dying back due to heavy shade from upper growth. You can improve light penetration to overgrown shrubs by using a technique known as thinning. Remove selective branches at their point of attachment, rather than giving a "haircut" to several branches at once. Proper thinning should not mar the plant's natural beauty and does not stimulate excessive new growth.
The best time to thin evergreens is in late winter or early spring before new growth begins. Light pruning may be needed later to shorten branches, especially if shrubs are in formal shapes or hedges. Broad-leaved evergreens that flower in spring should be pruned after they have bloomed. Spent flowers should be removed to prevent seed formation and encourage new growth. Overgrown, broad-leaved evergreens that have become bare at the bottom can be rejuvenated by pruning several of the oldest branches to the ground each year in early spring. This practice encourages new growth at the base of the plant. After repeating this procedure for several years, you'll have a completely rejuvenated shrub.
Pine, spruce, and fir trees generally require less maintenance pruning than other evergreens. Pruning is generally limited to removing dead or damaged branches close to their point of attachment or just beyond a healthy branch. These trees produce all of their yearly growth in condensed shoots called "candles." To encourage more compact growth, the tips of the new candles can be cut back halfway, before the needles unfold. Candling usually occurs between late April and mid May, depending on the weather. Cutting the shoot tips after the needles have developed will result in a misshapen plant, as these trees cannot replace their growing tips. To preserve their natural beauty, pine, spruce and fir trees should be planted where they will have ample space to grow naturally.