My husband recently increased the time on each irrigation station to compensate for the hotter, windier days. This was essential for the 50-year-old trees, mostly cottonwoods and pines, which were started when the lawns were put in decades ago. Since tree roots grow where water is, all these old trees have roots throughout the lawns. Tree roots, especially those of cottonwoods, extend out from the trunk four to five times the height of the tree, which means pretty much everywhere we have lawn. If I water just enough to keep the grass alive, it’s not enough for the trees. The longer run time helps. People sometimes remove their lawn in the interest of saving water. Conserving water is admirable and I applaud it. But, when there are established trees in or near the lawn, grass removal and subsequent cut off of all lawn irrigation can cause trees to decline and/or die. Someone might think putting one or two drip emitters near the trunk of the tree to water it will be enough, not realizing how far away from the trunk the roots extend, that absorbing roots are not near the trunk in established trees, or that a couple of emitters can’t provide enough water. If you have already removed lawn around old trees, an option is to wind soaker hoses in concentric circles out to the dripline and beyond — wherever the tree was getting water before — and run them or multiple drip emitters for hours at a time for a deep soak. A better approach might be to remove the lawn out to the dripline of the tree canopy, add a two-inch to four-inch layer of mulch and put a dozen or more emitters in that area, but trees may still suffer. The best way to completely remove grass would be to do it gradually. Start one year by winding soaker hoses or adding multiple spray emitters under the tree and out to the dripline. Train the tree with deep watering from those alternative sources for a spring, summer and fall while you gradually reduce and then finally eliminate the lawn watering when the trees go dormant. This will allow the tree to develop absorbing roots wherever you are deep watering. After the trees have gone dormant, remove the lawn. Do remember to continue to water the trees through the remaining fall and winter, especially after the shock of lawn removal. Deep watering is always best for trees. If possible, make sure your trees are on their own drip system rather than a lawn system and add more emitters each year as the trees grow. Ideally, keep grass away from under the tree’s canopy. JoAnne Skelly is Associate Professor & Extension Educator Emerita at University of Nevada Cooperative Extension. Reach her at skellyj@unr.edu.
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