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Oaks need water in drought

“Give an oak a chance,” said Mariposa County Master Gardener Coordinator Kris Randal, for whom oaks are a passion. That chance includes giving them some water during our record drought, contrary to most previous advice.

She and Greg Giusti, a forest and wildlands ecology advisor for Lake and Mendocino counties, are offering guidelines for keeping oaks from dying of thirst.

“If we consider what is being asked of the trees in this drought, it gives us pause to rethink our approach,” said Giusti. “In some parts of the state, oaks are being deprived of water for as long as nine months, creating extreme water stress.”

Here is the advice of the two oak experts: give oaks a good soaking once a month during the driest season. This should be done around the “drip line” of the tree – the area directly below the outstretched branches, not near the trunk. A soaker hose is good for this.

Let the water run (but not run off) until the water has penetrated 12 to 18 inches into the ground.

You can test this with commercial devices or simply use a long probe such as a screwdriver: If it comes up with signs of moisture at the tip, you’re good. The preferred time to water is early morning or late afternoon-night, so less water evaporates.

Randal emphasizes that it is important, especially with oaks, to let the soil dry out completely between waterings because oaks are susceptible to a root fungus that grows in warm, damp soil.

Infrequent but deep watering is the key.

“Obviously, an irrigation plan can be considered only if one might not have water to spare or if not under severe water rationing,” said Giusti.

While oaks are strong organisms that a single pest or disease usually cannot kill, said Randal, extreme water stress, combined with attacks from such enemies, can weaken them to the point that death is possible.

But don’t be too quick to morn. If your oak leaves are turning brown or falling, wait. In severe drought, oaks can shut down their leaf systems to save water.

“Always wait till spring,” said Randal. “If your tree leafs out, it’s still alive. And in this drought, give it extra time to leaf out.”

Other trees in your yard should get the same treatment, but with different schedules and water amounts.

“If you have a favorite tree, that’s the one to choose,” Randal said. She cited shade trees, special decorative trees or trees meant to make a statement.

More information on watering for mature and young trees is available online at saveourwater.com/trees, which has advice and a link to how-to videos.

Mariposa County Master Gardener

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