Pruning shrubs and trees

Understanding the task

There is nothing more important in the care of trees and shrubs than pruning. Far too many plants are lost or irreparably damaged by inept approaches to this truly simple art or by disregarding its necessity altogether. Not only is pruning an almost inseparable adjunct to the health and vigor of woody plants, but it is an essential factor in achieving the maximum attractiveness of the landscape. Even though the mechanics of a particular job may require the services of a professional, the home owner benefits by understanding the work which he is paying a professional to do.

Pruning for plant health

Pruning to enhance the health and vigor of a plant entails the removal of dead and dying wood and split or broken limbs, removal of crossing and interfering branches, amputation of stubs which have resulted from the breaking of limbs or from improper cuts in previous prunings, and reduction of the top to offset root injury such as may be caused by transplanting.

Prompt removal of dead, broken, and dying branches not only improves the appearance of the plant but makes early healing of the wound possible, lessening the chance that harmful decay organisms may enter.
To remove dead branches from trees, cut back to the nearest living crotch, with shrubs even to the root, although it takes off live wood. Studs, which retard proper healing, also should be removed promptly, since open wounds provide beckoning doorways for decay organisms.

When a branch crosses the center of the plant or crosses nearby limbs, remove it while it is still young, for crossing branches, as they grow, eventually may rub against one another, causing abrasions that may become focal points of infection. Moreover, removal of crossing branches increases the attractiveness of the plant.

Cutting branches The correct way and incorrect ways to cut off a branch. (A) The cut is made correctly, close to the trunk, and prompt healing results. (B) The cut is made too far from the trunk, with healing precluded. (This incorrect pruning results in a stub (C) which, if not removed promptly, causes (D) decay.

When two branches grow close together, almost parallel, forming a narrow crotch, one of them should be shortened or removed, because a crotch thus formed is more likely to split than when three or four branches lead out from virtually the same point, or two branches separate at a wide angle. It is especially important to avoid narrow crotches when the branches grow upright, for in the case of young tree if such shoots start near the ground and are not checked a double trunk may result. When such leaders are seen to be developing, the one bearing the best distributed branches should be kept and the other pruned away as far as possible without creating too great a gap in the tree.

Pruning the top of a plant to bring its size into line with the ability of the root system to supply plant nourishment, especially moisture, often promotes the vigor of the plant. In general this should be done with newly planted shrubs and trees. Whenever roots have been cut or disturbed extensively, such pruning should be undertaken to preserve the balance between top and roots. It is especially important with collected wild plants, great portions of the roots of which are usually left in the woods from which they were taken. Prune to maintain as nearly as possible the natural form of the plant. It is better to thin out entire branches than to shorten their ends.

If a plant does not show lack of vigor, or root destruction is not strongly indicated, do not prune severely to promote extra vigor. Pruning merely for pruning's sake may damage or destroy a plant, and even when done remedially there is always a possibility that the tree may never recover completely from severe treatment.
The general treatment for cavities in trees is to remove all traces of rotted wood and coat the exposed surfaces with antiseptic and wood-preserving substances. Cavities must not hold water. Sometimes it may be desirable to fill them with sawdust and asphalt, tarred wood blocks, or concrete.

The use of blocks in cavity filling assures that the trunk is flexible. Flexibility is highly important for in the face of high winds a tree must be free to sway and ride the blast. Any point of resistance within the trunk becomes the focus of greatest stress and strain; and if the trunk is too stiff at the filled cavity something often snaps.
The result is that the filling of the cavity loosens, the bark at its margin opens, water seeps in and stands, and a new process of decay begins. Winter may freeze the standing water, causing greater injury, and within a few years the effectiveness of the original cavity is lost and the tree is worse off than when first treated.

Cavity fillings prepared in early spring have actually fallen out the following autumn. A walk along a tree-lined street often demonstrates the effectiveness of various cavity if solid, they will show openings on their sides, but if blocks, they are healing well and the wound is closing.

Pruning plant for form

If a plant does not fit its surroundings, attempts to prune it severely to proper size and shape usually produce disagreeable results; it is better to dig the misfit out and put an appropriate plant in its place. Pruning for form means the light trimming that is needed to maintain the natural outline of plants in informal plantings and the frequent and severe pruning and shearing that is required to shape plants to formal design, as is the case with hedges.

In naturalistic plantings remember that the plant is most attractive in its natural form, although it may sometimes need some help to attain and emphasize its characteristic shape; this may entail the removal of wild-running branches, or thinning to reduce the number of branches.

Evergreens in informal plantings often require light pruning to maintain their natural outline in the artificial situation to which they are removed. Moreover they may become scraggly and open, al- though they grew compactly when young. To cure this, the longer branches may be cut back at appropriate forks inside the crown, thus checking the fastest-growing shoots and allowing the remaining limbs to branch out and make the plant denser. If taller growth and maintenance of symmetrical form is sought, however, the central upright shoot must never be cut away.

If the leader has been destroyed, however, it is possible to develop a new one. Tie firmly to the main axis of the plant a strong, light pole reaching a foot or more above the point at which the new leader is needed. Select from the branches at the base of the destroyed leader the strongest, best placed one, and tie it to the pole in as upright a position as possible. Eventually it should become set in this position and aligned as the main axis of the tree.

When evergreens grow too large for the space in which they stand, they may be held within limits by removing the leaders and pruning the side branches back to the nearest crotch, but the gardener must remember that if this treatment is applied repeatedly the plants will become highly formal, losing their natural outline characteristics. Care must be taken not to remove too much foliage since with many coniferous species new foliage does not develop on the parts of branches at which needles have died.

Except when used in highly formal designs, deciduous shrubs should be pruned merely to maintain the natural shape and outline. Unless the plant must be tailored to fit a set pattern, its natural appearance is most desirable.

With hedges, smooth formality is achieved by shearing them once or twice a year, and even more frequently. Informal effects are obtained by cutting away branches that are growing too far out of line. These should be cut away at a crotch.

Pruning for flowers

Woody plants may be pruned to achieve a maximum of bloom or to develop larger clusters or greater size and quality of individual flowers. Those grown for flowers should generally be pruned after they have finished blooming and before new flower buds form.

Spring-flowering plants form their flower buds in late summer or early fall of the year before they bloom. Summer and autumn flowering plants form their flower buds early in the year in which they bloom. Thus, spring and early summer flowering plants are pruned while in active growth, and late summer and autumn flowering plants may be pruned any time after blooming and before growth starts the next spring. Hardy late bloomers may be pruned at any time in this period, but the tender ones are best left unpruned until spring. Tender plants which are pruned may suffer winter kill farther back from the ends of cut branches than from uncut ones.

Flowering trees and most shrubs require the removal only of weak or crossing branches and of wood which no longer bears flowers freely. Shrubs which develop several shoots from the ground demand the removal of the older ones from time to time, the intervals being governed by the kind of plant, its age, and the conditions in which it grows.

Removing the older branches or the stem to the ground helps to keep a flowering shrub young and vigorous and to maintain it within bounds. In some species no shoots are allowed to grow more than 7 years old, others 10 years, while in many only 5 years is allowed. This control is determined by the flowering habits of the species, the best age of the wood for flowering, and the objective effect sought by the landscape designer. Whatever the governing factor, controlled age of shoots is a practical form of shrub rejuvenation.
When to Prune. The time for pruning may be considered in terms of results.

Winter pruning

Wounds remain dormant and do not heal until spring. In the process of healing they also induce the formation of adventitious buds near the wound. These buds sprout and develop into wood growth, a process which gave rise to the maxim, "If you want wood, prune in winter." Winter pruning also involves a double operation, since winter kill cannot be anticipated and a second pruning must be undertaken when the tree begins to sprout and reveals winter injuries.

Early spring pruning

Healing is fast when pruning is done at this time but there is an excessive development of adventitious buds resulting in sucker growth not only around the wounds but within the entire tree because of the great circulation of food in the sap and the general urge of growth characteristic of spring. There is also the likelihood of "bleeding," or excess flowing of sap, with some species, which not only wastes valuable nutritive substance prepared by the plant but provides a possible attraction for injurious insects and fungi which may become serious. Maples especially are bleeders, but wounds on trees with resinous sap, such as coniferous evergreens, do not bleed and often the dried sap provides an effective covering for the wound.

Late spring pruning

This is an excellent time for pruning since wounds heal well. Care must be taken, however, not to remove too much foliage since this may expose the base of the tree, depriving it of the natural shade which provides an umbrella over the sur- rounding earth, decreasing evaporation of soil water and protecting against drying out. Exposure caused by removal of too much foliage often causes a severe shock to some species of plants.

Summer pruning

Wounds may heal slowly but few if any adventitious buds form in the new callous tissue developing around the cuts. Moreover, the extra food within the tree system is utilized more readily for the production of flower buds instead of wood buds. Again, too much foliage must not be removed, but more may be taken off at this time than during the late spring pruning period for it is during the hot spells of June and July, especially if they are dry months, that such excessive stripping of foliage is serious.

Fall pruning

This is the best time in many ways since the pruning does not shock the tree severely. Limbs that are weak or bad may readily be removed; they may be lost anyway if weighted heavily with snow or ice during the winter. Wounds may harden and heal slightly, but they do not heal completely before spring. While adventitious buds form, their development is not in as great quantity as results from winter pruning. The disadvantage of fall pruning is that a second pruning will have to be undertaken the following spring to remove winter kill.

How to prune

Although it can be used only on comparatively small branches, a sharp knife is the best instrument for pruning. Pruning shears crush the branch and slow the healing process. Two-bladed hedge shears are better than pruning or clipping shears. Saws are necessary for bigger cuts, but only fine-toothed ones should be used.

A properly made cut heals most promptly. In cutting twigs make a diagonal stroke starting just about even with the lower edge of the bud and ending just above it. If the cut is too close to the bud, the branch may die because the adjacent parts dry out. If too much wood is left above it, the wound cannot heal and the twig beyond the bud dies.

If you are removing some of the current season's growth to control a vigorously growing plant which has no side branches to which to cut, make the cut toward a strong bud pointing in the direction which you desire the new growth to take.

In removing stubs or larger limbs, make the cut at a crotch almost paralleling and near to the supporting branch. The cut should be made through the collar, or swelling, at the base of the branch; if the cut is made beyond the collar the wound in many cases will not heal.

Be sure that bark is not torn away from the tree by the removal of branches. This may be avoided, in the case of a larger limb, by making four cuts, the first two to remove the limb and the other two to remove the stub which remains. Determine the place at which the final cut will be made, the spot at which the stub will be removed. Then make the first cut 1 or 2 feet out on the limb from the lower side, the distance depending on the size of the limb. This cut should go about halfway through the limb. Make the second cut 3 or 4 inches out, from the top side. When this cut reaches a sufficient depth the limb will break off and no bark will be torn from the tree. Next, make the first cut to remove the stub by cutting through the bark into the branch, from the lower side. Then make the final cut from above, in line with the preceding cut. If these two cuts are properly made and meet, the stub comes off without tearing the bark below. To handle the stub with greatest ease, make it as short as may be done safely to prevent tearing of the bark when the branch is being cut. It may be necessary in some cases to split away the stub a portion at a time to make its support easier as the operation nears completion.

Tearing of bark also may be prevented in removing a limb by propping up the limb or supporting it with a rope. Stubs must be removed because they are harmful to the health of the plant, rotting quickly and allowing decay to enter trunk or limbs.

Unless bleeding of the wound forces a delay, cuts should be treated with a protective material as soon as they are made. One of the best is ordinary shellac, applied generously and immediately around the cut edge of the bark and covering the edge about an inch each way. House paint, creosote, or some good preservative should then be applied to the central surface of the cut, overlapping the shellac but not reaching the bark. Repaint the cut surface whenever necessary until new bark grows over the cut surface.

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