Most people have a very common misconception which is that a tree’s roots never venture out beyond it’s canopy. People will literally only water a larger tree as far as it’s branches go and stop. This is far from the truth.
In reality a tree’s roots grow, venture out and settle far beyond it’s canopy. Most tree roots are settled within the top 12” to 18” of the soil. When watering older trees, we recommend that you offer up a deep level of irrigation to the entire area beneath the canopy. You should also venture out several feet past the canopy and water the surrounding areas as well. Never water the area directly around the trunk, this can encourage tree rot.