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Pruning Trees
by Dr. Oneida Cramer

The shade of the old oak tree comes under the scrutiny of arborist, Sam Hill of Partners Tree Care, who cringes when he drives around so many Dallas neighborhoods with obviously over pruned trees.

?There are a couple of different ways you can over prune a tree,? Hill said. ?But the most common one is to take all the interior growth out?strip all the green foliage so that there is just a tuff at the end of the branch.? Allowing more sunlight to reach the grass or to highlight the trunk of the tree are reasons for the excessive pruning; but the extra light can sometimes cause sunburn on the tree itself, especially on the trunk and major limbs. Red oaks are particularly susceptible to sunburn, as are maples, pear trees, and any tree with a thinner bark. On the other hand, the thick bark on live oaks and cedar elms give these species some immunity.

?Taking out the inner foliage concentrates all the forces right out there on the tip,? said Hill. ?Instead of making trees safer by pruning, we tend to make them less safe with improper pruning.? For instance, the wind against the length of a defoliated branch, which can?t move so easily, tends to cause a great deal of breakage. And over thinning the lateral branches in the limb causes the plant to redirect its growth hormones out to the very tips. So, the limbs elongate even more and become even more vulnerable.

Trees die from three broad reasons, according to Hill. (1) Environmental degradation includes the problem of pollution, too much soil on top of the roots, chemical spills, and environmental injury. (2) Mechanical failure takes place if the tree is blown over or loses a large part of its canopy. (3) And parasites, mostly fungal rather than bacterial and viral, can cause major infestations.

Arborists minimize inoculation of oak wilt, for instance, by avoiding any pruning in oaks from February 1 to June 15 because of the presence of the beetles that transmit oak wilt during these months. Other than this window of restrictive activity, pruning healthy trees can be done almost anytime during the year, according to Hill. But for weaker trees, Hill suggests waiting until winter. Pruning to train growth should begin in young tree and include an objective plan for fifteen years. Check the web page at the Florida Chapter of the International Society of Arboriculture, ( for a pruning timetable.

Proper pruning is supposed to improve trunk and branch structure, remove or shorten low limbs, and thin the canopy for better airflow and health maintenance of trees in the urban setting. Trees in the wild have done just fine evolving for millions of years without the need for pruning or fertilizing, as we know it. But the difference between the trees in the wild and those in the yard is the homeowners? desire to grow plants under their shade trees. And pruning makes this cohabitation possible.

?We use shade trees to accomplish two goals,? said Linda Tycher of Linda Tycher & Associates, Landscape Architecture. Number 1--to accomplish the proper shading of the residence, which means, in some cases, letting in sunlight and warmth, and in other cases, blocking out extreme weather conditions. The second way to use shade trees is to create a sense of place and a design framework on landscape that sets the stage as an outdoor room.

?It?s an art,? Tycher said. ?You have to have the knowledge much like interior design.? Whether starting with a new yard or adding to a mature yard, the elements of design should be considered whenever planting new trees, shrubs, or bedding.

?You have to establish mechlins-how the beds are going to curve and how the shapes of the beds are before you can place trees,? said Tycher. ?A lot of times, people just come in and plant trees. And that?s really not a good idea. Its more important to design the garden as a whole.? Think of the eventual height and spread of the tree ten fifteen years ahead. And consider that some ground covers or beds may bring about a tree?s demise. For example, Shumard red oak, which cannot tolerate over watering, may die when circled by beds of impatience because the impatience?s requirement for water far exceeds the tree?s tolerance. Bald cypress, in contrast, requires lots of water. So, landscape architects plant bald cypress on the down side of a slope in a lower area, not on a hillock or burr where water runs off quickly. Do a bit of research and learn the requirements of your trees. Then try to create a landscape that?s also an appropriate habitat for the vegetation.

Consider choosing shade trees that are indigenous to this area. Among the many trees acclimated to this climate and soil, Tycher recommends a few of her favorites, the red oak, live oak, cedar elm, Chinese pistache, native pecan, and bald cypress. She also loves in ornamental trees the redbuds, Japanese maples, dogwood, and of course, the crape myrtles. The soft look of the southern wax myrtles and the blooms of the vitex trees are also beautiful. When planting the sweetgum, a tree with magnificent fall color, Tycher stresses the need to be careful about getting the just right acid-sandy soil. One very popular tree in the area, the Bradford pear, Tycher tends to avoid because of its lollipop shape and dense foliage.

The practice of stimulating the growth of foliage through fertilizing recently came under heated debate during the Ohio Chapter of the International Society of Arboriculture held in May, according to Hill. Plant pathologists presented research that fertilizers, rather than endowing trees with the ability to resist insect invasion as once believed, actually made the trees more appealing to predatory insects.

All creatures on earth require the same basic elements for optimum growth, Hill said. And nitrogen is one of those basic elements. Soil enriched with nitrogen fertilizer stimulates the plant to grow foliage also enriched with nitrogen. And when insects eat the nitrogen-enriched plants, they too become nitrogen enriched, thus leading researchers to conclude that fertilizing the soil ultimately fertilizers the insects.

Fertilizer also suppresses the plants? ability to resist disease infestation because the fertilizer directs the bulk of the plants? limited supply of energy towards growth, leaving little energy left for the two other important life processes--reproduction and defense against disease.

Thus, the meeting concluded that the current recommendation, 2 to 6 lbs. nitrogen/1000 square feet of root zone, tended to cause people to over fertilize their trees. And so, they drew up a new recommendation--1 to 2 lbs. nitrogen/1000square feet of root zone. Hill recommends using the slow release fertilizers, such as Osmocote, or contacting an arborist, who has access to other slow releasing compounds.

-by Dr. Oneida Cramer
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