Weather extremes and the prospect of continued global warming require us to understand the special care trees need in the event of drought.
Drought stress develops in plants when the available soil water becomes limited. As this happens, young roots are killed outright, reducing the plant's ability to absorb sufficient water. The soil also becomes hard and compact as it dries, reducing oxygen to the roots. If landscape plants (trees, shrubs, and ground covers, especially evergreen types) do not receive adequate rainfall or supplemental watering, heavy plant loss is likely.
Water trees and shrubs during extremely dry soil conditions. If you have to choose, water your trees and not the grass since grass will turn green again when water is available. For water conservation, it is best to not water your lawn at all. Trees, on the other hand, will show subtle signs of drought, wilting, or dropping leaves. However, they can be seriously injured or die without water.
When watering trees, shrubs, and other landscape plants, remember that they absorb water and nutrients through their roots, most of which are in the upper 1 to 2 feet of soil. The goal is to keep plant roots moist, but not wet. Constantly saturated conditions also can damage roots