Whether it's keeping a large-growing species in scale or giving a shaggy tree a trim, smart pruning can improve a tree's appearance. Some trees show their attractive bark or flowers more effectively when pruned. Cut off water sprouts and suckers for neatness.
Diseased branches can sometimes be removed before they infect the rest of the tree. (Be sure to dip the pruning blade in a 10 percent bleach solution between each cut to avoid spreading disease.) Dead or broken branches can be removed before insects burrow inside to make a home.
Pruning also alleviates potentially hazardous situations. Trimming branches that threaten power lines avoids serious problems, but leave this task to the pros. Large dead or dangling branches should be removed, as well as branches that could interfere with vehicles or lawn mowers. Branches that contact the house on windy days should be cut before they cause damage.
Wrong: Don't cut too close to the trunk. Flush cuts are too large and delay the sealing of the wound.
Wrong: Don't cut too far from the trunk, leaving an ugly stub which can give insects an entry point. The wound cannot seal until the stub is removed.
Right: Make the cut just outside the branch collar (the swollen area where the branch meets the trunk). The branch collar contains chemicals that speed the formation of callus tissue that seals the wound.
Larger branches are best removed in three steps.
1. Make a shallow cut on the underside of the branch, about 4-5 inches from the trunk.
2. Cut the branch off about 2-3 inches from the initial cut. When the weight of the unsupported branch causes it to fall, the initial cut keeps the bark from peeling down the side of the trunk.
3. Make the final cut, removing the remaining stub. Make this cut just outside the branch collar: the slightly swollen area where the branch and trunk are joined together.
Narrow, V-shape junctures are inherently weak and are subject to breaking off in wind or ice storms. To prevent V-shapes from causing problems, remove one of the stems while the tree is young.
Make your first cut 4-5 inches above the union of branches, then make the finished cut about 1/4 inch above the union. On larger limbs that were pruned too late, cut one side back to a lateral branch so that the other side begins to dominate.
Some trees naturally tend to form narrow, V-shape junctures, but not all require corrective pruning. Native elms, hornbeams, serviceberries, hickories, and Osage orange trees are generally strong enough or small enough that little corrective pruning is needed for structural purposes, except to remove crossing branches that might rub.
Others, particularly maples, flowering pears, ashes, and light-wooded willows and basswoods, should be watched closely and given early training so they avoid structural problems as they grow larger. Bradford pears are notorious for developing weak angles because too many limbs often form at one point on the trunk. If these limbs are thinned early when the trees are still small, many more can be saved from storm damage.
The following is a list of trees that tend to form V-shape junctures:
As a survival instinct, some trees sucker up from the ground after they are felled. When multiple stems grow, they become more prone to storm damage, and the natural shape of the tree is compromised.
To prevent this, save the straightest stem and remove all others. If you want to grow trees in clump form for aesthetic reasons, make sure the multiple stems are well spaced and that they spread away from one another so they will not rub as they grow larger.
Forked trunks are less stable than a single trunk and often grow together, leaving a hollow cavity where insects and rot can further weaken the tree. The tree will eventually split, or one of the trunks will break off.
To prevent this, remove one of the forked trunks while the tree is still young. Cut as close to ground level as possible, making the cut at a slight angle so rainwater drains off the stump. Take care not to damage the bark on the remaining trunk.
When cutting back stems, avoid making the cut halfway between buds. This leaves a long portion of the stem to wither and die, which is unsightly and invites insects and disease.
Instead, make the cut about 1/4 inch above a bud. Choose a bud facing the direction you wish new growth to follow, and angle the cut in the same direction.
Too many branches bunched together are unsightly, and can cause problems. Plus, smaller, undesirable branches interfere with the development of larger branches.
Thinning these lateral shoots will let the remaining branches get better air circulation, water, and sunlight. This is especially important with trees that tend to form multiple crotches at a single point on the trunk, creating a weak zone.
When a branch breaks off in the wind or is cut too far from where it joins the tree, a stub remains. This dead remnant prevents a protective callus from closing the wound and provides insects with an entry point. Once insects make inroads, moisture and rot can take over.
The discolored wood in the stub shows the damage the tree sustained as rot spread. When cutting off an old stub, be careful not to cut into the swollen callus tissue forming at the base of the stub. It's needed to seal the wound.
Applying a seal over pruning cuts or even broken branches is no longer necessary. Allowing a wound to breathe is the best way for it to heal faster.
Dressings sometimes retard the growth of callus tissue (the swollen area) and may trap moisture. Most arborists now use tarlike wound dressings only for special purposes. Some insecticidal wound applications might be used, for example, to discourage beetles from visiting and possibly spreading oak wilt disease. Other products may be used to inhibit regrowth, or suckering, from the pruning wound. Some applications may allow regrowth, but at a reduced rate. These plant growth regulators are frequently used when pruning trees under power lines. The treatment allows the tree to regrow, but lengthens the time before another pruning cycle is necessary.