Pruning Myths

By Marilyn Loser

Pruning can affect a tree's longevity, health, and resistance to storm damage. Many myths surround the trimming of a tree. General tree myths were covered in the June 10 column.

Myth: Prune back the crown of the tree to compensate for any roots lost during transplanting.
Fact: Trees should not be pruned when planting except to remove broken or dead branches. The crown of a young tree should not be cut back to compensate for root loss. Little pruning is necessary in the first three years after planting unless the tree has a double leader. In that case, remove the weaker stem.

Myth: Topping (the removal of the upper portion of a main stem) reduces the hazard potential of tall trees, can improve the health or structure of trees in poor condition, does no harm to healthy trees, and does not damage trees when performed correctly.
Fact: Topping is always a serious injury to the tree and usually results in serious, long term structural consequences regardless of technique. Negative impacts include 1) serious decay at the topping cut and poorly attached regrowth increasing the likelihood of branches breaking, 2) reduction of the tree’s energy producing capacity decreasing its ability to resist insects and disease, and 3) increased crown density requiring frequent maintenance for re-topping or restructuring.

Myth: Pruning trees invigorates them.
Fact: Pruning, particularly severe pruning, often results in the stimulation of dense, vigorous sprout growth. However, this production of vigorous growth consumes much of the tree’s limited energy, weakening its natural defenses.
The benefits of pruning are many, but there is always some negative impact from the loss of foliage. Reduction of the foliage mass, however small, means a reduction in the tree’s capacity to photosynthesize, thus reducing the energy available for all its life processes.

Myth: Making pruning cuts close to the trunk or parent limb will help the tree heal.
Fact: Trees do not heal in the sense human beings do.  They do not replace lost tissue; they cover injuries, such as pruning cuts, with new layers of wood. To minimize decay and promote closing of wounds, do not penetrate the tree trunk but retain the “branch collar” (the slightly raised areas surrounding the base of most branches.)

Myth: Paint pruning cuts to seal out insects and disease.
Fact: Research has shown that common wound dressings do not inhibit decay, do not prevent insect entry, and do not bring about faster wound closure. In fact, many of the commonly used dressings slow wound closure and seal in moisture, leading to infection.

Myth: When a tree has lost a significant portion of its root system such as in construction damage, the crown should be cut back to compensate for root loss.
Fact: Following root loss, unpruned trees seem to respond better than pruned trees. Obviously, any removal of branches will reduce the capacity of the tree to produce food in the leaves. Although the tree will probably lose some branches as a result of the root damage (if the tree survives the trauma), it is best to let the tree decide which ones. Pruning should be limited to hazard reduction at first. Later, after the tree has responded to the damage, further pruning may be in order.

Myth: If I prune a lot off my trees I won’t have to prune as often.
Fact: It is the reverse. When you prune a lot off your tree it encourages new growth at the areas where the limbs were cut. The tree may send off a flush of growth which is a shock response to the improper pruning. This will produce more growth which generates a higher need for pruning. If your trees are properly pruned it won’t be necessary to prune them more often, the trees will be more pleasing, you will enjoy more benefits from the trees, and you will save money from not having to prune your trees so often.

“God has cared for these trees, saved them from drought, disease, avalanches, and a thousand tempests and floods. But he cannot save them from fools.” John Muir, American Environmentalist