First, it must be understood that it will take a tremendous volume of water to totally replenish the soil moisture throughout the entire root zone of a large tree. Using a sprinkler irrigation system attached to a garden hose delivering 5 gallons per minute, it would take five days of continuous irrigation to water this one tree. Obviously, it will not be possible to totally replenish the moisture reserve in the entire root zone of a large tree with irrigation. Fortunately, however, wetting even a small portion of a tree s root zone will greatly reduce drought stress. Lawn irrigation typically has little impact on large trees.
Most homeowners irrigate frequently for a short period of time.
While this maintains enough moisture in the upper 3 inches of soil to keep the turf green, it provides little water to tree roots. Unless the turf is shaded, tree roots can not compete with the dense mat of turf roots near the soil surface. Maintaining a large mulched area under a tree or growing a less competitive ground cover, such as ivy, allows trees to utilize irrigation much more effectively. An effective method to reduce drought stress for a large tree is to use a soaker hose of some type. This provides a double soaker with reasonably uniform delivery over its 25-foot length.