PUBLICATION DATE: February 05, 2016
WATER TREES DEEPLY BUT INFREQUENTLY
By Ginger Easton Smith
County Extension Agent
We have certainly experienced some extremes in rainfall over the last several months! Since it has been dry for more than a month, it is time to water trees. The key to watering all plants in the ground is to apply the water infrequently, yet very thoroughly. This encourages deep and healthy root growth. Watering for short periods of time encourages shallow rooting which can lead to more drought damage.
Plants use water for basic functions such as photosynthesis and can’t live without it. During an extended drought, small feeder roots die and plants can’t absorb as much water, even after the soil is re-moistened. Worse yet, energy reserves are used to replace the lost roots.
Drought might not (although it might) kill a tree outright, but the stress makes it more susceptible to serious secondary insect and disease infestations, such as boring beetles and Hypoxylon canker disease, in both the current and following years.
Proper watering is one of the most important factors in tree health. The most common watering mistakes are watering too frequently and watering too lightly (shallowly). Both can result in tree injury, but I have seen many more plants damaged by overwatering than by under watering.
Deep water trees every three to four weeks, and shrubs once a week if we don’t get 1” of rain.
Irrigation systems designed to water turf do not sufficiently water trees–they need additional water. Water slowly and deeply in one or two applications so water doesn’t run off. Use soaker hoses, a regular hose, or a hose end sprinkler.
The general rule of thumb for trees is 5-10 gallons of water per inch of trunk diameter; use the lower end for healthy trees, and the higher end for stressed trees and those with roots covered in turf or groundcover, or located next to paving. Add enough water to wet the top 8-12 inches of soil. This may take several hours or more depending on how its applied, and you’ll need to use a screwdriver or metal rod to determine how deep the soil is easily penetrated (dry soil is very difficult to penetrate).
Most of a tree’s feeder roots, which absorb moisture and nutrients, are in the upper one or two feet of soil. On an established tree, roots extend out at least twice as far as the drip line. For a tree which has been in the ground less than two years it will be considerably less, check to see how far the roots extend.
When watering, cover as much of this root area as possible, beginning two to three feet from the trunk (do not water the trunk!), and going at least a foot beyond drip line if possible. It is better to wet a small area to 8-12 inches deep, than to only wet the surface couple inches over a large area. For more information, download “Tree Watering Tips–Caring for trees during extreme drought”, or watch a video by the Texas A&M Forest Service, at http://texasforestservice.tamu.edu/main/popup.aspx?id=14964, then scroll down to Watering Tips.