Growing the Desert Garden

Welcome to the Desert Garden, with garden coach Tyler Storey, where we talk about everything having to do with gardening and landscaping in the Desert Southwest. From composting to Cercidium and agaves to arugula — we'll cover everything you want to know to grow your own beautiful Desert Garden.

Monday, July 14, 2008

When Bad Things Happen to Good Trees: Part 1

Even in the Desert Garden, there are times when we could say that no water is better than wrong water.

Last week I was called out to look at a leaning Palo Verde tree. This tree is planted near a drive, on the North side of the house, in an area altogether about 12 by 12 feet; not ideal, but not bad. The tree had been growing well, even vigorously, and was nearing 20 feet in height. Then suddenly it took a dive at about a 20° angle towards the East, partly blocking the walk into the house.

As I looked at the tree, three things were immediately apparent: first, the soil on the West (opposite the lean) was clearly broken upwards, but only for about 12 inches from the trunk. Second, there was a single drip irrigation head right where the roots were pushing up from below, again about 12 inches from the trunk; there were no other emitters in the immediate area of the tree. Third, the soil was visibly saturated on the West and bone dry on the East.

How often was the irrigation system run? Every day for twenty minutes.

A couple of things about trees to keep in mind:

  1. Tree roots have three functions: roots convey water and nutrients from the soil; roots provide storage of sugars and starches; roots stabilize and anchor the tree in the soil.
  2. Tree roots do not "seek out" water. Roots do not have eyes, ears, noses, or any other sensory organ with which to find water at a distance. Roots do, however, proliferate in the presence of water, and only in the presence of water.

The diagnosis was clear: the tree was receiving frequent shallow water in a single small space on the West side of the trunk, and this had resulted in a small root mass; the root mass was probably no larger than 2 feet by 2 feet, probably only 18 inches deep, and predominantly on one side of the tree. The area above that root mass was continually moist and loose. Once the tree reached a certain size and caught the wind just right, over it went.

Palo Verdes are very drought-resistant trees; in this instance, it would have grown more sturdily — albeit more slowly — with no water at all.

The remedy was less straightforward. Once a tree begins to fall, it's difficult to get it back upright, and rarely is this a complete success in the long term. The hard-nosed, unsentimental, and practical response is to remove the failed tree, install a new tree, and re-work the irrigation to avoid a repeat of the same problem. In this instance, we did some judicious pruning to clear the entryway walk and to lessen the canopy weight in the direction of the fall. Next, rather than try to pull the tree back upright, we decided to temporarily support the trunk in its current position and immediately rework the irrigation to begin growing a much wider and deeper root system to support the tree. Any sturdy board with a bit of padding would have worked for a support, but the homeowner wanted the support to look nice, so he promised to build one and get it under the tree that day.

Postscript: A day later the support wasn't in yet, and that evening we were hit with a monsoon-season thunderstorm that dumped nearly an inch of rain in a very few hours. Down went the tree.

The morals of the story:

  • All trees should be watered deeply — to a depth of three feet and as wide as the canopy, or wider — and infrequently;
  • Things move fast in the Desert Garden, epecially when they start to go wrong;
  • Don't let the perfect (or the pretty) be the enemy of the good (with apologies to Voltaire); and
  • You simply cannot say "I told you so" to a man whose tree is laying flat on the ground; he already knows.


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