Q. Our Acacia and other trees in our neighborhood in Mesquite, Nevada, have leaves that are turning yellow. Is this from all the heat we’ve had or too much watering?
A. This extended heat wave requires you to water more often. But water long enough to wet the soil deeply. Avoid watering daily, particularly trees and shrubs. It is not needed if you water deeply. It is better for the plants if you don't. Instead, increase the number of minutes so that you can avoid watering every day.
Healthy plants can handle the heat. Leaf yellowing is not because of heat but because of either dry soils or soils that are continually wet. Continually wet soils can occur from daily watering. Watering desert adapted plants every day may cause their roots to “suffocate” from too much water.
Watering less often, but with larger amounts of water, forces roots to grow deeper and harvest water from greater soil depths.
Plants are lazy. Plants require more energy to harvest water from deep in the soil than from the surface of a soil. If water is applied to the surface every day, these lazy plant roots “slurp” up the surface water and hardly touch the deeper water, if there is any.
If water can be found deep in the soil and the surface of the soil begins dry, tree roots will be forced to grow and harvest water from these deeper, wet soils. This deeper growth improves anchoring of the tree and reduces “blow over” during high winds.If you are going to make a mistake when overwatering, make the mistake of giving the plant too much water rather than watering daily.