Wednesday, January 27, 2016

Pruning the Trees in Your Landscape by Peter Drake

Photo courtesy thegardenerseden.com
Accustomed, as we are, to regard trees as an integral part of our home landscape, we would do well to remember that the trees we commonly enjoy usually need our help to continue their life here. 
Beyond the willows and cottonwoods that have found homes along the rivers, streams and irrigation ditches, our Colorado Front Range foothills region is not generally hospitable to the varieties of shade and ornamental trees we’ve come to enjoy so much.  This broader climate zone still wants to be what it was before Euro-American colonization and settlement: a high plains desert, covered with durable grasses and low shrubs, and intensely vulnerable to climatic extremes which can split bark and easily kill top-growth, both new and old—as was graphically demonstrated in the November, 2014 and Mother’s Day, 2015 hard freezes.

Understanding this, we can develop a more holistic, care-taking attitude toward the trees in our yards and on our streets: We need to take the time to ensure they are receiving the consistent care necessary for healthy, even growth.  

Pruning, regularly and carefully, is a component of this consistent care.  It is as vital to a tree’s health as appropriate watering, fertilization and mulching, and it should be used as part of a care strategy involving all of these other components—both to ensure enduring aesthetic value, and proper safety of the people and property around the tree.  In what follows, we will review, step-by-step the best pruning practices for most shade and ornamental trees in our Colorado Front Range landscape.

Practice 1 - Observation: Long before you take snips, saws or loppers in hand, give the tree you intend to prune a thorough assessment.  Often, the best results are gained when you assess a tree repeatedly—perhaps three or four times a year, at different seasons, with leaf cover and without.  

Ask yourself the following: (1): Do any limbs or sections have abnormal swellings or blotches that could indicate the presence of a gall, canker or other fungal or bacterial disease in the tree? (2) Are there any limbs or sections which appear obviously dead, or distressed (prematurely browning leaves, split and peeling bark); (3) Are there any structurally unsound areas of the tree (such as water sprouts or other suckering growth; limbs that are growing so closely that they are either fusing, or rubbing, together; or areas within the trees where major limbs are forming either too narrow, or too broad, a “V” shaped crotch) which render the tree as a whole much more vulnerable to weather-related damage?  Assuming that any disease and distress is localized within the tree, and not indicative of a larger, tree-wide condition (you should always ask yourself whether your tree is afflicted with a more comprehensive, longer-range condition) both disease and structural issues can be gradually corrected through pruning.

 Practice 2 – Timing:  While most species of tree can be productively pruned at any time of the year, heavier pruning (the removal of significant, structural limbs) should wait for the winter dormancy period—which is to say: when the tree has stopped all growth and has shifted to storing its energy within is base root mass.  Assuming consistent weather patterns of chilling and warming, the best period in which to prune your tree falls between February and April. 

Pruning during this dormancy period can help ensure that your tree does not waste energy in new growth which is left vulnerable to weather extremes.

Practice 3 – Cutting Only What You Absolutely Have To: It is easy to continue cutting into a tree, once you have started.  Resist this impulse to ensure that your tree retains enough top-growth to bud, leaf out and continue its healthy lifespan through the spring and summer seasons.  

For disease or damage, focus only on what wood specifically looks diseased or damaged, cutting back only as far as it takes until you reach healthy-looking wood.

For reducing the density of the crown of your tree, focus only on sucker and/or waterspout growth, as well as limbs growing so closely together that they are in danger of rubbing or fusing.  Cut (as much as is possible) only the limbs that are less dominant, leaving the stronger limbs to preserve the structure and crown shape of your tree.

Practice 4 – Make Proper Pruning Cuts: Ideally, you should not be pruning out any limbs or branches over two inches in diameter, as this will minimize open surfaces on the tree that could be subject to decay.  Of course, incidents of disease or damage rarely involve ideal conditions, so your pruning cuts must be made in such a way as to preserve the “branch collar” (the junction of the trunk growth rings with the branch growth rings) and the “branch defense zone” (a mass of cells which activate the growth of wood over the pruning cut) as much as possible, for the tree to heal itself as swiftly as possible.

Depending on the species of tree, the branch collar will be more or less evident, but will show itself as a low ring of bark, jutting out from the trunk or parent limb of the branch to be cut, and extending all the way around the base of the branch.  

A three-step pruning cut is generally the best approach to prune off a branch or limb cleanly, without excessive damage to the branch collar, or branch defense zone: A first cut, underneath the branch, should be made 12 to 15 inches out from the branch collar; a second cut should then be made on the top of the branch, two to three inches beyond the first cut—which should allow the branch to settle and prevent bark tearing away from the underside of the branch.  Finally, a third, final cut can be made just outside the end of the branch collar.
Diagram courtesy Plantalk Colorado

By following these general practices, and adjusting them, as necessary, to the particular needs of the species of trees in your landscape, you can be better assured that your trees will have a full, healthy lifespan for your greater, shared enjoyment.

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