Native and established trees generally don't need any supplemental water. But should the weather turn particularly dry, they just might. Be sure to water them correctly.
By definition, established trees — those that have been in the ground for two or more years — seldom need supplemental water other than natural rainfall.
If they do need watering, say for an extended drought of five to six months, then there’s a correct way to do it.
When that time comes, keep these things in mind:
- The dripline of the tree is the key watering area. This is where the tertiary roots — those that absorb the most water and nutrients — are located.
- When watering a tree, the emphasis is on infrequent and deep. Infrequent means once every 30 to 40 days in the absence of effective rainfall – that is, a ½ inch over several hours. If we have a “good rain” then supplemental water is not needed. Deep is a slow watering that penetrates the top 6 to 10 inches of soil. Generally, for our area this is 1 inch to 1 ½ inch of water per application.
- Applying 2 inches of mulch beneath the tree 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. The more roots, the less supplemental water required. Trees that have been properly planted and established seldom need supplemental water.
Fortunately, we rarely have years like 2011-2013 where supplemental water for trees was truly needed. Then again, this is not an established tree’s first drought and there will be many more in the future. If we treat our trees well, there is minimal chance of them dying.