Extension Highlights: Pruning

EDITOR'S NOTE: This is the second of a two-part series about tree pruning.

Reduction of height and width may be necessary for several reasons.

Limbs may interfere with the roof or the side of the house; or the root system may be attacked by cotton root rot and it will be necessary to reduce the top and sides to compensate for root damage.

Before reducing height and width, there is one important rule to remember: Always attempt to cut back right to a side branch.

A cut made next to a side branch discourages development of numerous new limbs.

If a cut is made between side branches, this will encourage developments of new limbs.

This will result in the witches' broom effect.

Deciduous shade trees will often have a lopsided appearance especially when young.

One side will grow more rapidly than the other and if not corrected it will affect its normal shape.

When trees are dormant, they can be cut back to achieve a more even balance.

Again, it is necessary to cut back to side branches when bringing the lopsided portion back to the normal routine.

Making proper pruning cuts

Rapid healing of pruning wounds is dependent upon where the cut is made.

When removing limbs never leave short shrubs.

These often die back and serve as an entrance for organisms.

Mulberry and other trees produce a corky ring of growth where a limb originates.

The pruning cut should be made toward the outside portion of this "collar." If a tree does not produce this characteristic collar, then make the cut flush to the limb where it is growing.

Treating wounds after pruning

Pruning wounds should not be sealed with pruning sealers, as new research indicates the tree gives off healing compounds to heal itself.

Mulberry, chinaberry, California pepper, cotton wood and other soft wood trees are highly susceptible to disease invasion, so pruning cuts should be painted with a Bordeaux paste, a fungicide.

Caution: Do not use house paint or tar emulsion preparations on tree wounds.

They may not seal the wound or they may actually injure tissue that promotes healing.

Pruning or ruining

There is an old saying among professional gardeners in connection with tree pruning, "if in doubt, don't prune." Nature has a unique way of allowing trees to develop natural forms.

When this natural form is destroyed, trees will act accordingly.

If one limb is removed from a tree, there should be a reason for doing so.

Anyone who prunes for the sake of pruning, "because everyone else is" will undoubtedly cause problems that will be difficult to correct in later years.

Why not to "top":

eight good reasons

• Starvation: Good pruning practices rarely remove more than one quarter to one half of the crown, which in turn does not seriously interfere with the ability of a tree's leafy crown to manufacture food.

Topping removes so much of the crown that it upsets an older tree's well-developed crown to root ratio and temporarily cuts off its food making ability.

• Shock: A tree's crown is like an umbrella that shields much of the tree from the direct sun rays.

With the protection suddenly removed, the remaining bark tissue is so exposed that scalding may occur.

There may also be a dramatic effect on neighboring trees and shrubs.

If these thrive in shade and the shade is removed, poor health or death may result.

• Insects and disease: The large stubs of a topped tree have a difficult time forming callous.

The terminal location of these cuts as well as their large diameter prevent the tree's chemically based natural defense system from doing its job.

The stubs are highly vulnerable to insect invasion on and the spores of decay fungi.

If decay is already present in the limb, opening the limb will speed the spread of the disease.

• Weak limbs: At best, the wood of a new limb that sprouts after a larger limb is truncated is more weakly attached than a limb that develops more normally.

If rot exists or develops at the severed end of the limb, the weight of the sprout makes a bad situation even worse.

• Rapid new growth: The goal of topping us usually to control the height and spread of a tree.

Actually, it has just the opposite effect.

The resulting sprouts, often called water sprouts, are far more numerous than normal new growth and they elongate so rapidly that the tree returns to its original height in a very short time and with a far denser crown.

• Tree death: Some old trees are more tolerant to topping than others.

Some species do not sprout readily after severe pruning and the reduced foliage most surely will lead to the death of the tree.

• Ugliness: A topped tree is a disfigured tree.

Even with its regrowth it never regains the grace and character of its species.

The landscape and the community are robbed of valuable asset.

• Cost: To a worker with a saw, topping a tree is much easier than applying the skill and judgment of good pruning.

Therefore, topping may cost less in the short run.

However, the true cost of topping is hidden.

These include reduced property value, the expense of removal and replacement if the tree dies, the loss of other trees and shrubs if the succumb to changed light conditions, the risk of liability from weakened branches and increased future maintenance.

For more information, please contact the University of Arizona, Mohave County Cooperative Extension office at 753-3788.