Young trees

Some plants are sold as one-year whips--young trees with long stems and few or no branches. Most trees, however, are sold as two-year, three-year or older specimens on which structural branches have already begun to develop.

Prune at planting to remove only broken or damaged branches or roots, to remove branches that will not be suitable to form the main framework, or to shape the plant to a somewhat symmetrical form. Do not prune back the central leader of the tree unless you want no leader, as with certain small flowering trees or plants you wish to be multiple stemmed.

Early pruning to direct the growth of young trees is very important if mature trees are to function as expected in the landscape.

The growth habit of a plant and its landscape use determine how and to what extent the tree must be pruned. Trees with a central leader and a conical shape, such as conifers and some deciduous species, need little or no pruning. Trees with irregular growth habits, poor branch structure or vigorous laterals, such as sugar maple, may need considerable pruning.

Prune a young tree only enough to effectively direct its growth and to correct any structural weakness.

Branches selected for permanent scaffolds must have wide angles of attachment with the trunk for greatest strength (Fig. 12). The position of a limb on a trunk remains the same throughout the life of the tree. How high above the ground the first permanent branch should be depends on the tree's use. The lowest branch can be a few inches from the ground in trees used for screening or windbreaks, or 6 to 12 feet above the ground in trees over a street or a patio. Vertical branch spacing is important in many species for future dominance, structural strength and appearance of the tree.

On mature trees, closely spaced scaffolds may break up in storms more easily than more widely spaced ones (Fig. 13). Closely spaced scaffolds will have fewer laterals, resulting in long, thin branches with little structural strength. Major scaffold branches should be spaced at least 8 inches and preferably 10 to 24 inches apart vertically (Fig. 14).

Radial branch distribution should allow five to seven main scaffolds to fill the circle of space around the trunk. With radial spacing, branches radiate from the trunk like spokes on a wheel. Because no one limb is directly over another, they do not compete for light (Fig. 14).

Direct plant growth by pruning during the growing season as well as when the tree is dormant. During the growing season, pruning is usually confined to temporary shoots and branches that will not become permanent branches. Heading back the growing point or completely removing a shoot will reduce its competition with the leader or shoots selected for scaffold limbs. Remove or prune shoots that are too low, too close or too vigorous in relation to the leader and shoots selected to become the scaffold branches (Fig. 15).

During the growing season, heading back the tips of vigorous growing, temporary branches may be necessary to keep them in bounds and reduce competition with the leader and permanent branches.

A tree at planting may not be tall enough for the selection of any permanent lateral branches. If laterals are present below the height where the lowest permanent branch is wanted, they should be handled as temporary laterals. After two or three years, when the trunks of small trees are 2 or more inches in caliper, you can begin to reduce the number of temporary branches. Over the next two or three years, remove the largest temporary branches at each pruning to minimize the size of the pruning wounds (Fig. 16).

Mature trees

You can improve tree health and appearance by removing limbs that are dead, weak, diseased and insect infested. This also reduces sources of future infection and infestation. The steps for removing limbs 3 inches or larger are illustrated in (Fig. 17A).

Large limbs must be cut with a saw. The recommended procedure is to remove a large limb in two steps involving three cuts. Make the first cut on the underside of the branch 1 to 2 feet from the crotch. The undercut should penetrate at least one-third of the trunk diameter. Make the second cut 1 to 3 inches farther from the crotch than the first. The limb should split cleanly between the two cuts without tearing the bark on the trunk.

You can then make the third cut at the crotch with less chance of the bark's tearing and leaving a jagged cut surface. The position of this cut is important to ensure rapid healing of the wound.

Many trees form ridges on the top and bottom of branches where they are attached to the trunk (Fig. 17A and 17B). These are called shoulder rings. Pruning cuts should be made between the center ridges of these rings. The cut will not be flush or parallel to the trunk but will be out from it slightly, with the lower edge of the cut farther away from the trunk than the top.

Such a cut will form a smaller wound than a flush cut, and callus tissue will form rapidly to cover the wound. Callus tissue should develop uniformly around the edge of the wound (Fig. 17B).

Often shoulder rings are not present at branch attachments. The cutting position can be approximated by envisioning a line connecting the point bisecting the top angle of the crotch and a similar point bisecting the lower angle of attachment.

The structural features of a tree may be emphasized by moderate thinning to reduce density. The structure of dogwood, ginkgo and others can be maintained in the landscape by moderate thinning out.

Homeowners often attempt to control the size of trees by pruning. It is best to prune the tree as it begins to reach the desired height. Delaying pruning until the tree is much larger than you want it makes pruning more difficult and pruning cuts harder to hide, and it encourages excessive regrowth.
 

Thinning-out pruning can be used to reduce the height and spread of a tree (Fig. 18). Cut branches to lower laterals (drop crotching). Some limbs may be removed completely. A thinned tree retains its natural shape and is less subject to vigorous watersprouts than a headed or topped tree (Fig. 19).

Topping (heading back) is, unfortunately, the most common method of reducing tree size. It is more rapid than thinning, but the results are, in most cases, much less desirable. Regrowth is vigorous and upright from the stubs. The new branches form a compact head and broom-like terminals, and they may be weakly attached to older branches.

Bleeding of pruning wounds can be heavy on certain trees, such as birch, dogwood, sugar maples and elms. Bleeding of susceptible trees can be minimized by making small cuts--less than 3 inches in diameter--and pruning in summer. Bleeding is much more likely if severe pruning is done just before growth begins in the spring. Bleeding doesn't harm the tree, but if it is heavy and persistent, it may injure the bark below the pruning cut and cause slow callusing of the lower wound.

If large limbs need to be removed, or if you can't reach the limbs that need pruning, secure the services of a professional landscape manager. Landscape managers are trained in the art of pruning to retain the natural beauty of trees.

Protecting pruning wounds

Applying an asphalt emulsion or other materials to pruning wounds to protect them is of doubtful value. The purpose of these emulsions is to protect the cut surface from wood-rotting organisms and to prevent checking as the wood dries. When exposed to the sun, however, the coating often cracks. Moisture from rain, sprinklers or dew can then enter the cracks and accumulate in pockets between the wood and the wound covering. That moisture makes the wound even more susceptible to wood-rotting organisms than one with no wound cover application.

In some situations, for aesthetic reasons or for maximum protection, the practice may be justified. Allow the wound to dry before applying the coating to improve chances for good bonding. Examine the coating several times the first year and re-treat if the coating has cracked.

Split trunks, crotches or limbs can often be mended by restoring the damaged part to its original position and holding it there permanently. Professional landscape managers should be consulted to install bolts, screw rods or cables in trees when this work is necessary.