ORINDA – Irrigation is crucial for established trees, but in order to be effective, it’s important to follow proper procedure. For example, a common mistake people make with tree irrigation is watering the trunk. Since a tree absorbs water through its roots, watering its trunk doesn’t make much sense. Instead, water should be applied at the outside edge of the tree’s drip line, where the shadow of its canopy is cast upon the ground. It’s also important to provide an adequate amount of water—ideally, the water should soak down about a foot into the soil.
In addition to proper procedure, a great way to maximize the effectiveness of irrigation is to apply a 4- to 6-inch layer of mulch beneath the tree’s drip line. Besides reducing sun and wind evaporation, mulch adds beneficial fungi and bacteria to the soil as it decomposes, which improve tree roots’ ability to absorb water and nutrients. Since mulch decomposes over time, it should be reapplied annually.