Guidelines for Pruning Conifers

From How To Prune Coniferous Evergreen Trees by D. McConnell, R. Mahoney, W. Colt, and A. Partridge, U. of Idaho Cooperative Extension

Before pruning, consider your objectives, such as the desired size, shape, and density of the tree. At times, no amount of careful pruning will control the plant to your satisfaction. In such a case, removal and replacement with a different plant may be the best treatment. The dense growth characteristics of juniper, arborvitae, and similar species produce a dead interior zone where the twigs and buds are killed from severe self-shading. The dead zone limits the extent of pruning. If it is exposed by severe pruning, new shoots will not develop from the exposed area. The result is a deformed and unsightly plant.

After locating the dead zone, look in the live zone for limbs that can be completely removed or for limbs that are dead, diseased, or broken. If a branch is to be partially removed, make sure to leave a green shoot near the cut or else the limb will die. The green shoot will produce vigorous growth during the following growing season.

The growth habits of pines differ from the other evergreen species mentioned above. Pines do not develop a prominent dead zone because their open crown does not cause severe self-shading. Some lower and inner branches, however, will periodically die from self-shading and normal growth habits. Pines characteristically produce branches in groups, or whorls, an important fact to consider in proper pruning.

Again, before pruning, consider your objectives for the tree, especial concerning the size and shape. Small pines are often pruned to produce a pyramidal, Christmas tree form. Pruning will shorten the space between the whorls of a pine, producing a fuller, more compact plant. Begin by cutting back the central leader at the top to an 8- to 12-inch stub. This cut should be just above a well formed bud. If possible, select a bud on the north side of the branch in order to form the straightest growth. South-facing buds tend to grow outward rather than upward.

Next, prune the side branches around the top until they are 4 to 6 inches shorter than the central leader. Continue pruning the remaining side branches in a manner that will produce a uniform pyramid shape. If the leader of a tree has been broken, a side branch can be trained to become the new leader. This process would occur naturally but usually results in two or more branches competing with one another as multiple leaders. To prevent this, cut back the remnant of the main stem to a point just above the uppermost whorl of branches. Prune one of the branches to a length of 6 to 10 inches. Gently bend the limb to an upright position and hold it in place with a stake and string. Finally, prune the other branches in the whorl back to restore the pyramidal shape of the tree.

Pruning pines will stimulate bud development from the needle bunches below each cut. These buds will increase the density of the tree by producing more limbs. The branches of larger pine trees will respond in a similar fashion. Be sure to prune only the newer growth, leaving green needles on the cut branches to produce more buds. When pruning larger evergreen trees, it is often desirable to remove lower branches in order to improve access around the tree. As much as one-third of the crown of full-crowned evergreens may be removed without affecting the vigor of the tree. The lower crown, however, should only be removed when absolutely necessary. The fully crowned tree is obviously superior in beauty and utility.

When removing a heavy limb, follow a three-cut process as follows. Make the first cut 1 to 2 feet away from the base of the limb on the underside of the branch; this cut should be made through approximately one-third of the branch. Make the second cut from above, just outside the first cut; it should completely sever the branch.
Finally, make the third cut just outside the limb collar, parallel to the attached limb or to the tree trunk if attached there. When making this third cut, support the stub. This process will permit the basal cut to be made smoothly, without the risk of binding a saw or peeling the bark.

In larger evergreen trees, remove any dead or broken branches and any branch stubs. For branches that noticeably swell where they join the main stem, make the final cut at the point where the branch begins to flare. This leaves a smaller cut surface that will heal more rapidly. Also, any branches that appear crowded should be thinned to favor a single, stronger branch. Strong branches can be identified by the wide branching angle between the trunk and the limb.

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Tip of the Season: The winter is a wonderful time to enjoy your landscape from a different perspective. It is also a great time to examine your trees and shrubs and make some pruning decisions. Timing is important: spring flowering shrubs bloom on last year’s wood and are pruned soon after they bloom. Summer flowering shrubs bloom on new wood so are pruned before they bloom, while they are dormant, during the winter until early spring. Spring blooming trees are different and are pruned while they are dormant. Unless you prune severely, they will still flower in the spring.