Deep water for trees health |

Deep water for trees health

by JoAnne Skelly
Fall watering is more about keeping the trees alive than the lawns.
Kurt Hildebrand

The nights are freezing, but the daytime temperature were in the mid- to upper 70s this week. When the temperatures vary from freezing at night to warm days, it’s hard to know how much to water.

A neighbor asked me if I was turning off my sprinklers yet for the year. This requires draining all the lines on the in-ground sprinklers and draining and blowing out the drip lines. I also disconnect and drain all hoses, and put them away.

I’m not quite ready for shutting everything down. The trees are still in leaf and there will continue to be warm days for a little while. However, I have backed off the watering frequency, basing watering on daytime temperatures and winds. I disconnect the hoses, hose-end sprinklers and driplines from the faucets every night to prevent them from freezing. I water later in the day as well. My focus is to deep water the trees, soaking the ground to a depth of 15 inches or more. With deep watering I can irrigate once every 10 days as the weather cools.

I use a soil probe to test the depth of water infiltration, but a long piece of rebar or a long screwdriver will also work. I insert the probe into the soil hours after watering, once the water has had a chance to soak in deeply. I push it into the soil in a few spots around a plant to see how far it goes in easily and to determine the extent of coverage. If I meet resistance, it indicates the soil is dry, unless I have hit a root. I measure the distance the tool penetrated and water more if necessary to reach the right depth.

The goal with watering now is provide trees enough water to fill up their vascular systems for storage until there is enough precipitation, either rain or snow, later in the season to wet the soil deeply. Once the deciduous trees have lost their leaves, if nature doesn’t provide water, I will irrigate once a month throughout the fall and winter whenever the ground will absorb water. This means I drag hoses around or re-winterize the irrigation system each time I water. Monthly watering is especially important for evergreen trees, which continue to transpire water through their needles during the cold seasons, particularly when it’s windy or sunny. In addition, any newly planted trees and shrubs will need monthly irrigation too.

JoAnne Skelly is Associate Professor & Extension Educator, Emerita, University of Nevada Cooperative Extension. She can be reached at