Native and established trees generally don’t need supplemental water. But during prolonged drought, occasional watering may be helpful — but only if it’s done correctly.
Established trees — those that have been in the ground for two or more years — seldom need supplemental water other than natural rainfall.
But during an extended drought of five to seven months, they will require some additional water. Just remember there is a right way to water them.
Keep these things in mind:
The dripline of the tree canopy is the key watering area. This is where the tertiary roots — those that absorb the most water and nutrients — are located. Water the area approximately halfway from the dripline to the trunk and move the same distance beyond the dripline.
When watering a tree, the emphasis is on infrequent and deep. Infrequent means once every 20 to 30 days in the absence of effective rainfall — that is, a ½ inch over one-two days. Deep means slow watering that penetrates the top six to eight inches of soil. Generally, for our area this is 1-¼ inches to 1-½ inches of water per application.
Applying no more than two inches of mulch each May and September beneath the canopy and beyond the dripline helps reduce the amount of supplemental water necessary. Mulch reduces water evaporation and cools the soil, which in turn encourages root growth. Trees that have been properly planted and established seldom need supplemental water.
Fortunately, we rarely see years like 2011-2015 where supplemental water for trees was truly needed, but we may be reaching that time again.
On the other hand, this is not an established tree’s first drought and there will be many more in the future. Look at our Natural Areas! If we treat our residential trees well, there is minimal chance of our trees dying.
By Mark A. Peterson, a conservation project coordinator for San Antonio Water System. With over 30 years of experience as an urban forester and arborist, Mark is probably the only person you know who actually prunes trees for fun. When not expounding on the benefits of trees and limited lawns, you’re likely to find him hiking San Antonio’s wilderness parks or expounding on the virtues of geography and history to his friends.