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Master Gardener Journal  


S P E C I A L   F E A T U R E



Summer Tree Care: a Life or Death Issue

by Lenora Stewart,
Master Gardener & Certified Arborist



Proper summer care can be a life and death issue for trees in the low desert. Native trees are "built for the desert," with genes that contain information making it possible for them to withstand drought. Some trees native to other deserts and regions also have strategies that make it possible to survive here under adverse conditions. However other, non-native trees are simply ill suited to our area, and are therefore prone to problems. So when choosing a tree, it's important to know something about its needs.

At the present time we are experiencing a drought. This means that you will need to provide water to insure that your trees have enough moisture stored in their leaves, branches, trunks, and roots to sustain them during the summer months, when they are is growing and expanding, and transpiration is occurring. Otherwise, trees can be thrown into stress. Then if further stresses occur, on top of those caused by drought, the health of the tree can be compromised.

One thing that can really stress a tree is pruning. Regular pruning is NOT necessary. Keep in mind that trees grow and produce leaves and branches for a reason. I'm not saying that it is NEVER necessary to prune, but too often pruning done for the wrong reasons. If you prune to keep a huge tree small, perhaps you planted the wrong tree. Or it could be that you are overwatering and overfertilizing, causing the tree to grow too big too fast.

Pruning during the summer deprives the tree of leaf area that it uses for shade as well as food production. There are many trees that have been thinned and pruned to the point that they provide no shade-even to themselves! That kind of excessive pruning exposes the tree's bark to intense and massive amounts of sun. Just as you would sunburn if you stood out in the sun all day without proper covering, so does the tree!

Heat is an issue in itself. Decomposed granite under or around trees absorbs and then reflects the heat and sun. This makes it even more intense! Block walls, glass, structures, and water surfaces all reflect and/or absorb heat, and can stress nearby trees!

In order for trees to have enough water, don't wait until the tree is dying to water it. Water deeply but infrequently all year. During the winter you can water less often, but water deeply far enough out from the trunk to get water to the entire root system. Remember: the largest percentage of the roots are at the drip line. Watering once every 4 weeks during the winter may be enough. During the summer, the same tree may need to be watered every 7 days or so. A drip system with one or two emitters next to the trunk of the tree that comes on every other day for 30 minutes is okay when the tree is newly planted, but watering should be reevaluated once the tree has been in the ground for a month or two. After that, assess and adjust the watering every few months.

Another important consideration is how trees are staked and tied. It is not always necessary to stake and tie newly planted trees! If it is necessary (to keep the tree from falling over), do so with the idea that as soon as possible stakes and ties should be removed. Many, many times they are installed and never checked again! The ties become tight around the trunk of the tree, cutting off much of the life-giving fluids that flow up and down the vascular system just below the bark.

So, be aware of your trees during the summer. Keep in mind that it is extremely hot out there, and there are many ways that trees are stressed. Since trees grow more rapidly during summer months and ties can become tight and strangle the tree, check those stakes and ties frequently. Make sure that your trees get nice LONG drinks when they get water. And especially during the summer, resist the urge to prune-AT ALL! Think like a tree!

Maricopa County Master Gardener Volunteer Information
Last Updated April 29, 2003
Author: Lucy K. Bradley, Extension Agent Urban Horticulture, University of Arizona Cooperative Extension, Maricopa County
© 1997 The University of Arizona, College of Agriculture and Life Sciences, Cooperative Extension in Maricopa County
Comments to Maricopa-hort@ag.arizona.edu 4341 E. Broadway Road, Phoenix, AZ 85040,
Voice: (602) 470-8086 ext. 301, Fax (602) 470-8092