When the tree is a sizable one, say 10 to 15 feet tall, it is often more convenient to do the pruning at the time of transplanting before the tree is put into the ground. First trim the ends of jagged roots. Then prune the top by taking out weak branches, those nearest the ground if a clear trunk is desired, those which are too close to a neighbouring branch, any crossing branches, or those which spoil the symmetry of the subject.
Trees with thong-like roots will need to have their tops pruned more severely than those with fibrous roots. The amount of the top growth to be cut off depends on the kind of tree and whether it naturally makes plenty of fibrous roots, such as Euonymus, and hence is easily transplanted, or whether the fibrous roots are sparse, as in Oak and Hickory. In general it is advisable to cut off about one third from the current shoots. Do not cut back the leader unless it is injured. If, after a few weeks of warm weather in the spring, the new shoots do not appear to be thrifty or if there is no sign of any growth, more cutting back is indicated.
If the trees were growing in a nursery, close planting may have been deliberate so that the lowermost branches were killed by insufficient light. Such trees, when planted in the open, are vulnerable to sunscald unless the trunk is protected by wrapping it with burlap or with specially made crepe-paper strips, or the trunk and branches may be sprayed with an anti-transpirant such as Wilt-Pruf. These protectants should be left in place until the head has grown to such an extent that it provides ample shade for the trunk. If the tree has two leading shoots, the weaker should be removed; otherwise an undesirable V-shaped crotch may develop.
It is worthwhile to look over newly planted trees to see if there is any trouble that can be rectified by pruning, paying particular attention to the V-shaped crotches, which are a source of weakness. They are very likely to form on trees whose buds grow in pairs. Sugar Maple is particularly prone to these crotches. The remedy is to remove one of the arms of the V, or if this leaves too big a gap you might get by with shortening the weaker one. Also look for branches which cross and rub each other, and cut off the less desirable one.
If the tree is supported by stakes or guy wires, they should receive attention. Possibly the tree can get along without them, in which case remove them. If they need to stay in place another year, be very careful to avoid having the ties so tight that there is danger of the trunk becoming strangled by its own growth.
Pruning established trees
This varies according to the object in view. If the tree is young and handsome, thinning out undesirable branches when the tree is dormant is the correct operation. Shorten any projecting branches that spoil the ideal outline, and when there are two branches which cross and rub each other, remove the less desirable one. If the tree is already large enough and the foliage is ample to cause dense shade, which for various reasons can be undesirable, the pruning should be done when the tree is fully leafed out in August.
This is preferable to pruning it when it is dormant because it will slow down future growth and immediately let more light reach the ground beneath the tree. Usually this can be done by cutting off fairly large limbs, making the cuts parallel with and close to the larger parent branch to avoid leaving stubs.
Because there are no growing parts on the stubs, there is no reason for sap to flow to their extremities; hence they die. The healing callus makes every effort to close the gap, but it is unable to do so. Meanwhile disease-causing organisms may get to work and decay may extend into the trunk or the large limb.
To do a good job of making a major wound, the cut should be made close to the trunk or to the branch from which it originates.
The removal of a large branch usually requires three cuts, the first about a foot from the trunk, making an undercut by sawing upward until the saw binds. Then cut from above about 1 inch from the first cut to remove the branch. This will leave a stub which can be supported by one hand while it is being cut off parallel to the branch or trunk on which it grew.
The reason for doing it this way is to avoid the possibility of the falling branch tearing off a large strip of bark from the trunk or parent branch. To promote quick healing, the wound ideally should be longer than it is wide. It may be desirable to make the wound in the shape of an ellipse by cutting into the bark above and below with a knife or chisel. If this is done the wound should be protected by covering it with a polythene plastic film or spraying it with an anti-transpirant preparation such as Wilt-Pruf. However, I would advise waiting for a time, before making the wound larger, to see if it will callus naturally.
There are differences of opinion among tree men concerning the desirability of protecting tree wounds made when pruning. The consensus seems to be that some protective substance should be applied, at least to the larger wounds—those 2 inches or more across. The dressing should inhibit the germination of spores of disease-causing organisms, prevent the checking (cracking) of the wood, and at the same time be non-injurious to the living tissue of the cambium. Shellac or a paint made of zinc oxide and raw linseed oil is conveniently obtainable and fairly satisfactory.
Soot or lampblack may be mixed with the paint to make it less conspicuous. Also asphalt paints can be used with good results, or a paint especially formulated for tree wounds may be obtained from garden supply stores.
Pruning mature trees
One of the reasons for pruning trees is to maintain and enhance their beauty. This does not necessarily require a great deal of pruning, because, ideally, the natural shape of the species should be retained as far as possible. This is not always feasible, because of spatial limitations which may require pruning to reduce the size of the tree or to slow down its growth.
Many trees, especially coniferous evergreens, when grown as specimens in the open with no competition with other plants, normally are clothed with their branches from the ground up. This may not be desirable in a home landscape because the owner may want to utilize the ground beneath the tree either for planting shade-loving subjects or for an outdoor living area.
High-headed deciduous trees with a clear, clean trunk of at least 6 feet are desirable for shade and also for street planting. This may require the removal of branches below the head. In some cases it may be necessary to spread the pruning over several years because otherwise the trunk may suffer from sunscald.
Before you start to prune a tree it is advisable to study it thoroughly. There should be a reason for every cut that you make when pruning it. It is always safe to cut off any dead branches, also those which have been injured by wind. When two branches get together so that they cross and rub each other, one of them should be removed. If this cannot be done without spoiling the symmetry of the tree, the branches may be fastened together at the point where the bark is being abraded. This can be done by boring a hole through both stems and inserting a stove bolt of suitable length.
The head and the nut should be countersunk. Treated in this way, the branches are held rigidly together and grafting will take place, which will remove the danger of spores of disease-causing organisms obtaining access to the tree through the wound. If the tree is not growing compactly, shortening the branch tips will force into growth buds that otherwise remain dormant. If there is an opening caused by the loss of a limb, it may be possible by pruning adjacent branches to direct the growth in that direction.
If the pruning is done in such a way as to make a well balanced tree while it is young, there will be but little need of pruning as it approaches maturity. V-shaped crotches usually are weak and whenever possible should be eliminated by cutting out the weaker of the branches. It is an impossibility to avoid all V-shaped crotches in trees such as Sugar Maple, and it may be desirable to cable two branches together and put a bolt through the tree toward the base of the crotch.
The time for pruning is late winter or very early spring. There are exceptions, however, with the trees which "bleed" profusely when they are cut toward the end of the dormant season. Among these "bleeders" are Sugar Maple, Birch, Walnut, Yellowwood, Beech, and Hornbeam, which should be pruned in September or October.
The tools required are lopping shears and a pole pruner or pole saw. The latter may be useless to shorten flexible branches because they wobble so freely that it is almost impossible to keep the saw in one cut. If you cannot do the job with these tools, it is advisable to get professional tree men to do the work.
When large mature trees are in question, pruning them is usually a job for a professional, even if his price does seem a bit steep. But it is better to pay it rather than a hospital bill, or for a funeral director, for you or a member of your family. It is as good as a circus to watch these tree men work on large trees. They are as agile as Tarzan and know exactly how to get around in the tree and the importance of using safety equipment. If, however, it is a case of removing a branch not too far from the ground, you may be able to do it yourself. Do not forget there is a right way and a wrong way of cutting off the branch.
Trees sometimes grow too large
There is nothing static about trees. At times they may grow too large in the positions they occupy. This is most often seen in plantings near the house or in foundation planting. Usually this trouble is caused by selecting wrong planting material. It is not unusual to see forest trees planted in situations where a height of 6 feet, usually less, is desirable.
For a while these trees can be kept down by annual pruning, but ultimately the time will come when it is necessary to remove them and start all over again from scratch—this time choosing slow-growing varieties that do not rapidly grow out of bounds. Sometimes the problem can be solved after a fashion by pollarding—either annually or at intervals of two to five years.
Old devitalised trees may sometimes have their vigour renewed by cutting off up to one third of their top growth when they are dormant. Good judgment is necessary to insure that enough is cut off to be of benefit but not so much that it results in the production of a thicket of sappy water sprouts. In general, the cuts should be made close to branches pointing in the direction in which you wish the trees to develop.
Trees sometimes garrote themselves. When wayward roots grow around the trunk, or around other roots, expansion by subsequent growth often results in strangulation. Sometimes the tree is able to free itself from its own snare by breaking the offending root. I have such a one on my own place, but in this case the root was comparatively small and only a small part of the circumference of the trunk was involved, so that the vigour of the tree was not greatly impaired. Often, however, prompt remedial surgery is required when injury is first noticed.
Sometimes the condition develops below the surface. If the tree is not healthy and there is no other known cause—insect pests, fungus disease, gas, or a bad soil condition—girdling roots should be suspected; especially if, in addition to symptoms already mentioned, the trunk does not flare naturally at the base; in the top picture the "flare" has not yet been affected. If girdling roots are the cause of the trouble, carefully digging away the soil near the trunk should disclose them so that they can be dealt with.
Girdling roots may occur on naturally regenerated trees, but more often in those which have been transplanted. In the first case, the roots may have been diverted from their normal outward-spreading course by an obstruction in the soil which set it on the wrong tack. In transplanted trees, cramming the roots in a hole too small to allow for proper spreading may be a source of later trouble.
It is well to look critically at the root system when transplanting a bare-root tree, and if any of the main roots look as though they are bent on mischief, cut them out if they can easily be spared; otherwise manipulate them and hold them in place by short stakes driven in below the soil level. By the time the stakes decay, the roots probably will be fixed on an innocuous course of travel.