Pruning

This time of year lies betwixt the two tree pruning seasons. Non-native trees should be done already and the desert adapted trees' time is coming up in April and May.

Proper pruning enhances a tree's chances to grow and mature properly. Poor pruning leads to tree problems resulting in quickly seen affects or many times long term problems. Discussions with noted arborists in Arizona support the supposition that the leading cause of tree problems and the shortened life of trees is directly linked to improper pruning.

Pruning removes limbs from trees. The limbs sport leaves and the leaves should be considered the center of the tree's life. All other parts of a tree, or plant act as support systems to the leaves and in return all the energy for all the other parts to grow is manufactured in the leaves. Roots supply the raw materials. The limbs hold the leaves up to trap light energy.

Removing leaves reduces the overall energy levels within the tree. And by the act of removing a limb the tree reacts to heal the wound and replace the missing parts. This action draws down the stored energy reserves and the long term affect is shortened life.

Proper pruning is more art than science. Keep in mind that if limbs need removing for safety (near roofs, blocking stop signs, etc.) or health (broken or diseased limbs) it should always be done and anytime of the year. For any pruning including the above or for heigth reduction or thinning out you should always keep these few rules in mind. If you follow these rules your completed job will look unpruned to the casual observer and the tree will be healthier.

Rule number 1: Never remove more than 1/3 of the tree's total leaf canopy in one year. If more pruning is needed then save some for next year. This is the most common mistake on younger trees but older trees also get butchered.

Rule number 2: Always remove a limb back to where its connected to its parent limb or trunk. Or cut it back to where another limb gowing from it.

This cut back to a side limb has the caveat that its diameter must be at least 1/3 the diameter of of the part removed. This rule alone should shoot holes in the poor practice of 'stub' pruning seen so frequently on mulberry trees. Following this rule prevents stub pruning from ever getting started. If, hoever your tree is stub pruned you can not correct and are stuck with annual butchering.

Rule number 3: Two thirds of the trees foliage should be lower than the rest. Trees in nature guide this rule. Rarely is seen a tree with most of the foliage in the to 1/3 of the tree nor do trees look like a large beach umbrella with a single trunk and flat spreading top. This is a common look after many people finish with trees. Most trees in nature form a silohette pattern remenescent of a mushroom's shape. This should be the model to guide pruning efforts.

Rule number 4: 80 to 90% of all wood removed should be done with 5 or fewer cuts. In other words a few selected cuts are much better than many small cuts. This demands more pre-cut planning and visualizing what will be left before making the cut.

And finally, Rule number 5: Topping is not acceptable pruning except for safety reasons as under power lines. If bids for pruning use the term 'topping', you'd be wise to get more bids. Topping is simple and usually results in a profusion of shoots rendering the tree more sussecptible to wind damage. A tree with proper heigth reduction pruning will still maintain the look and shape of the tree, just shorter.

Keeping these rules in mind and remembering that one definition of a tree as 'a self-pruning plant

Written by Terry Mikel, College of Agriculture and Life Sciences, the University of Arizona, 602-470-8086.
Material originally appeared in Arizona Republic
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