Pruning Needled Evergreens
Needled evergreens that are not grown for hedges or topiary usually don't need much pruning other than to remove dead, diseased, or damaged branches. When removing these branches, cut back to their point of origin on the main stem or to a healthy lateral branch.
Keep in mind that junipers, arborvitae, chamaecyparis, hemlocks, pines, spruce, and firs generally do not have live buds on old wood. Therefore, pruning to control shape or size should be light and confined to a portion of the new growth. Never cut shoots back into the old leafless wood.
Most needled evergreens should be allowed to develop their natural form. They should not be sheared except to create formal shapes since shearing results in a very dense shell of needles at the outer regions of the plant and causes excessive shading of the interior regions. This in turn leads to premature dropping of inner needles creating what's often called a dead zone in the center of the tree. The above mentioned evergreens do not regenerate new branches or needles from old wood to fill in the dead zone.
Corrective pruning of pines, spruce, and firs should be done while the trees are still young. Once they are overgrown, corrective pruning cannot be done without destroying their natural shapes. If the main stem of young specimens of these trees have unusually long internodes, which creates a very open plant, pinch off about one half of the new growth on the lateral branches in early June before the new needles have lengthened. This will promote more branching and a denser plant. However, this pinching should only be done once or twice and not routinely every year since it may lead to excessive shading of the interior of the tree. To restrict the upright growth of these trees, similar pinching of the terminal growth may be done. If a young tree should develop more than one leader or terminal shoot, remove all but one. If a leader is damaged, it can be replaced by tying one of the branches in the top whorl to a vertical brace.
Low-growing and creeping junipers can sometimes become overcrowded. In that case, remove entire branches by selective thinning, or cut back stems to lateral branches pointing outward. Do this in early spring and do not leave stubs. If some pruning is needed because of winterkill or disease, cut out the affected shoots as just described.
Of the needled evergreens, yews and hemlocks are the most tolerant of shearing, which is why they are so often used for evergreen hedges. Shearing of these should be done in spring after most of the growth has occurred, but be careful not to cut back into the dead zone with hemlocks. Since they produce live buds all along their stems, yews can be cut back as far as desired. However, if hard pruning is needed to rejuvenate an old plant, it should be done prior to new growth in spring.
Written by: Ron Kujawski