Folks, it’s a hot, dry summer here in central New Mexico. No surprise, you say — we live in a desert. Even for our location, though, it’s hot and dry. This creates a little conundrum for us: keeping our landscape plants growing while using water efficiently.
This applies especially to trees because as large plants with lots of leaves, they need regular adequate water for their size and species to remain happy and continue creating positive benefits for your yard and the city as a whole. Call that a biological law and reality. As temperatures go up, trees’ water demand goes up. That is a good starting point to keep in mind — in times of drought, you should water your trees a little more frequently than you would in a year with abundant rainfall.
It turns out that over 90% of the water that comes into a tree simply escapes through the leaves as water vapor; the tree keeps very little water inside to grow. This loss of water vapor provides the “suction” that causes more water to enter the root system. It also cools the leaves and keeps them within comfortable working temperatures. Someone once said trees (and plants generally) have figured out a way to guide the natural movement of water from soil to atmosphere, channeling it through their bodies and using it to grow and function, which is one part of the water cycle. Having trees increases moisture in the air, allowing your swamp cooler to perform better.
Trees “drink” very differently than you and I. We have one fairly large mouth into which all the water goes. However much we need, we have one target to hit in order to drink that water. Trees, on the other hand, take water in through their tiny, young roots out in the soil. Water has to get to a lot of soil in order to hit enough of those “mouths” to matter. A lot of tree irrigation eventually fails because there are only a few emitters (and those are often too close to the trunk). Those few emitters cannot put out enough water to satisfy the tree’s demand, nor do they wet enough surface area. (See examples in the photos below.)
What matters to a tree is the volume of water it has to work with. That volume is entirely dictated by the volume of soil that is holding water. And THAT volume is dictated by the surface area that received and absorbed water. The key is to disperse the water throughout the main root zone and do it in a way that allows the water to soak in where applied and not flow to low spots on the ground (which often are gutters. Science has found that most tree roots are located within the top three feet of the soil surface and quite likely even more shallow in landscapes that have not been deeply irrigated for the life of the tree, which is a common condition in Albuquerque.
To properly water your trees, you will need some sort of irrigation system. It could be a bucket you fill from the sink or a state-of-the-art sensor-controlled automated drip system. But somehow you need to put water on the soil surface in a slow, controlled manner so that it can soak into the soil where it is applied. While buckets and hoses work, their simplicity makes them very labor intensive. In-line emitter drip tubing, laid out in a spiral or concentric circles, does a much better job. Once in place, these drip systems can be set to run for two to four hours at a time, about once a week during the hottest part of the year and less often during other seasons. Irrigation improvements qualify for the Water Authority Treebate. See our rebates here.
The ideal target area to irrigate is both theoretical and grounded to the reality of the site. Imagine a donut shaped area centered around the tree trunk. The trunk sits in the center of the donut hole. The body of the donut begins halfway between the trunk and the edge of the branch canopy and extends some distance beyond the edge of the canopy. This theoretical donut represents the ideal critical irrigation zone.
Now enters site reality — maybe there is a house or driveway or sidewalk covering part of the donut (or all three, with the tree located in a tiny unpaved space). We don’t want to encourage root growth at the house foundation, so don’t water within a couple of feet of it. Similarly, where concrete or asphalt covers the soil, root growth is moisture-limited and concentrated immediately under the impervious cover and under any planned or accidental cracks that allow rainwater to slip through. Ideally, we don’t want to water next to the pavement. The more of the donut that is unavailable for watering, the more often you may need to water the limited areas of open soil. Even so, it may simply not be enough soil volume to support the tree, which will then decline. In that case, replace it with a nice xeric shrub!
Learn more here:
How to Make a Tree Watering System.
Best Practices for Watering with a Drip Irrigation System
