Although we are still in the throes of winter’s fluctuating freezing temperatures and, therefore, not at the best time to prune your trees, we thought we’d get a heads up on preparing you for pruning once temperatures even out (and after the first year of tree growth).
The type of tree should always be considered when pruning as this influences the method used to shape the tree and the tools needed. Trees native to climates with hardwood forests typically grow vertically as they compete for sunlight. Desert-adapted trees, however, compete for water so they tend to grow nearly as wide as they are tall, often developing branches that can extend to the ground. This growth pattern should be considered when pruning desert-adapted trees. The main purpose of pruning a tree is to encourage healthy growth and to enhance the natural form of the tree. Regular pruning can prevent damage during monsoons and proper tools and method will ensure that the tree heals quickly to prevent insect infestation and damage to the tree.
Ideally the best type of pruning is periodic light thinning rather than infrequent, major pruning. The general rule to pruning desert-adapted trees is 80:20. No more than 20% of tree foliage (or the main canopy) should be removed at one time and 80% of the area pruned should be new growth on the outer third of the canopy. (Refer to the left diagram).
Regular pruning will help you notice dead or diseased branches that need to be removed. It is generally better to frequently remove small branches than to occasionally remove large ones. Fortunately, most desert-adapted trees need minimal pruning if they are placed in areas where they have room to grow and will not obstruct walkways or other plants and trees.
We recommend pruning your tree only after the first or second year of growth. If a tree is pruned too early or too much is removed, you run the risk of removing branches that are needed for photosynthesis for the tree and you could end up starving the tree. As much as 60% of all photosynthesis for the Blue Palo Verde happens on the surface of its young branches. As the tree grows, first remove branches that cross each other (rub against each other) or are starting to obstruct walkways or other plants. Also, remove any dead or diseased limbs. If you are pruning to influence the shape of your tree and are uncertain about how to trim it or what to remove, first seek the advice of a certified desert landscaper or an arborist. You can always post questions on our forum here and our Arborist will answer them.
When pruning, use sharp tools for cleaner edge cuts that reduces the time needed for the tree to heal. Also use the correct size pruners or saw for the thickness of the branch being removed. Refer to the drawing on the right for different types of pruning tools. The angle and position of pruning cuts will significantly affect the rate at which the tree will heal. Improper cuts will increase the chance of tissue dieback and insect infestation as it takes longer for the tree wound to close. Cuts should be made near the branch bark ridge but not beyond it (refer to the diagrams below). Do not leave short stumps sticking out, a common mistake. Prune directly above a bud or lateral branch at about a 45 degree angle (refer to diagram 2 below), as this will ensure correct and speedy growth of the cut branch and healing of the tree wound.
If you are pruning a tree with thorns make sure to wear protective gear like eyewear, long sleeves, and sturdy leather gloves. Also use long handled pruners not only make the cuts but to pull the cut branches out and away from the tree.
Remember, when it comes to pruning if you are in doubt about how or what to prune, wait. You can always remove later but can never add back.
Below are some useful references for additional information, diagrams, and tips. If you have questions about pruning, please post them on our Ask the Arborist forum here and our volunteer Arborist, Erik, will answer them.
Erik the Arborist, on our forum: http://vpaaz.org/STForum
http://www.aridzonetrees.com/AZTimes%20Horticultural/Pruning%20Practices%20for%20Desert%20Trees_2002.htm (diagrams used in this blog)
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