Overwatering damage to trees and shrubs is an overwhelming problem usually as the result of the misuse of underground sprinkler systems.
Plants need water to survive. Insufficient amounts or too much water will cause plants harm and can be fatal. The roots of a tree must pick up oxygen from the soil as well as water. If the soil is saturated with water, there is no room in the soil for oxygen. This is why it is important to know how to properly water your trees and shrubs.
The symptoms of overwatering show up slowly over time. Growth is slowed. New leaves are yellowish and smaller than normal. Leaves may wilt. Roots will shut down and may die. If the Overwatering continues over many years, you may see die-back in the tops of your trees or early fall colouration.
How Much and How Often
Let nature help out. Try to supplement natural rainfall; do not try to replace it.
If your sprinkler system is on every night for 15-20 minutes, your trees may be slowly drowning from the lack of oxygen. Long, deep watering is best for trees. Usually an all night watering (8 to 10 hours) once per month will be sufficient. Frequent light watering is not beneficial. It is important that the soil dry out between watering. Shrubs need to be watered every two weeks. Use enough water to saturate the soil (8-10 inches) and then stop. To make sure you have soaked the ground deep enough, dig a hole 5 inches deep and check the soil moisture.
To check the water conditions of the root environment, dig a hole underneath the crown of the tree. Soil moisture is adequate if the soil can be made into a ball with little pressure. Injured trees need more frequent watering, usually once every 3 weeks.
The Right Methods and Equipment
Do not water a mature tree at its base. This does very little good and can cause root crown rot. Instead, use a sprinkler to cover the area under the branches. We have found that a soaker hose turned upside down is the best. A rotating sprinkler will work well, however, during the day a large amount of the water will evaporate before reaching the soil. Or learn to program your sprinkler so you can modify the program as needed and have an on/off switch installed.