June 21, 2018

ALERT! Oaks May Need Extra Water


Property owners might want to give their oak trees a long drink of water, according to the Resource Conservation District of the Santa Monica Mountains (RCDSMM).

Experts have long recommended that homeowners not irrigate coast live oaks (Quercus agrifolia), especially during the warm season. Such watering encourages fungus, which can weaken, and ultimately kill, the evergreen tree. But this year is different, says Rosi Dagit, senior conservation biologist with the RCDSMM.

Coast live oaks are usually resilient, but a third winter of drought has killed many throughout the mountains. Thirsty trees are also more likely to succumb to harmful beetles. How to tell if your oak is under stress? “Look for uniform changes in color from green to light brown,” says David Whitney, a deputy forester with the County of Los Angeles Fire Department.

You might also notice oozing or staining on the truck or numerous twigs that are turning brown and falling off, adds Dagit. These may indicate increased beetle activity. A certified arborist or the County forester can let you know whether your oak is infested.

Homeowners can mimic late-spring rainfall using a 100-foot soaker hose, set on slow drip, for 24 hours once a week. Lay the soaker hose around the tree’s drip line, or just inside the drip line. If the tree shows signs of recovery after a month, stop watering. “Do not place the hose at or near the base of the tree or allow water to soak the trunk,” says Dagit. “Doing so will benefit pests more than it will help the tree.

“Despite our warmer weather, it’s not too late in the season to water these trees, says Whitney. “We’re not going to save every oak in the Santa Monica Mountains, but for certain trees in people’s yards, this could be beneficial.”

Coastal live oaks are keystone species in the Santa Monica Mountains. Some experts say having a mature oak tree as the focal point of your yard can add $5,000 to $30,000 to the value of your home.

The RCDSMM works with landowners to conserve natural resources throughout the Santa Monica Mountain. District biologists offer consultations on sustainable landscaping. For information, call (818) 597-8627; or e-mail: keepyourgreen@rcdsmm.org.