How and When to Water Your Trees and Shrubs
If you have mature trees and shrubs in your yard, you're in luck. You don't have to worry about watering them in most cases. New ones need water after you've planted them for about a year to become established. Rain does most of the work, but it helps to give even your mature trees and shrubs a good soaking now and then in the summer and for the first few years after planting.