06/05/2022
DO YOU KNOW HOW TO WATER YOUR BIG TREES?
Last year Spokane experienced a triple-digit heat dome from June 26 through July 2. Hundreds of our wonderful urban trees were damaged because homeowners failed to give large landscape trees any additional water, or they applied water too often and not deep enough, or they watered close to the tree trunk and not at the dripline where trees take up the majority of their water. In other words, much of the damage could have been prevented.
As climate change continues to worsen, extreme heat events are expected to become more frequent and more deadly to humans, animals, and plants. Learning how to apply supplemental water in the summer will become ever more essential for our landscapes.
According to the WSU Spokane County publication linked below: “Roots of established trees typically extend further and reach less deeply than is often thought (or commonly taught). It is not unusual to find roots of a tree extending 2 to 3 times beyond the horizontal reach of its branches. In most soils, tree roots will not extend more than 3-4 feet in depth. Soils provide insufficient oxygen beyond that depth.
The goal of deep watering is to achieve pe*******on of water to a depth of at least 3 feet. Use the dripline, the outer perimeter of the tree’s branches, to determine the area outside of which watering efforts should be concentrated. The finer, non-woody, “absorbing” roots (those directly responsible for moisture and nutrient uptake) are usually found in this outer area.
The use of sprinklers or soaker hoses is not advisable to attempt deep irrigation. They can result in shallow flooding that impedes oxygen and carbon dioxide movement through the soil, causing a
suffocating effect. Watering or “feeding” tubes can create vacuoles in the soil that result in root death. The best deep-water application device is the simplest: the bare end of a garden hose.
Set the hose end down at the dripline. With close observation, adjust the rate of flow out the hose to match the rate of acceptance by the given soil (to avoid runoff or puddling). To achieve pe*******on
to the desired depth, more time will be required for clay than for sand. In loamy soil, water will pe*****te at about 6 inches per hour. That comes out to about 6 hours per entry point. Use a
probe, sampling tube, or shovel to make the initial rate and time determination. A manifold device multiplies the end of the hose and eases the effort and time involved in deep watering.”
For more information please read the following:
DEEP WATERING — WSU Spokane County
https://s3.wp.wsu.edu/uploads/sites/2076/2021/06/C092-Deep-Watering-of-Trees-21.pdf
TREE CARE GUIDE — Denver, CO
https://www.denverwater.org/residential/efficiency-tip/tree-care-guide
Graphic courtesy of the Denver Water Department
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