Irrigating Oaks in the Drought

Jul 15, 2015

Irrigating Oaks in the Drought

Jul 15, 2015

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To water or not to water….an oak. That's the question. If only Shakespeare could answer our questions as eloquently as in his plays. In a state where the motto has become “brown is the new green” as people allow irrigated lawns to die, more and more folks are concerned over the potential loss of oak trees in their garden. These trees not only provide shade and aesthetic appeal they also can provide tremendous real value to a piece of property. In some cases, fixture oaks have a sentimental story…a place where a wedding occurred; or a child once had a swing hanging from its branches; or even memories of planting an acorn with a child and watching the sprout grow into a magnificent tree.

The extraordinary drought has caused many to reconsider the mantra of “don't water oaks” as excessive water can lead to the development and spread of root pathogens that can weaken or even kill oak trees. But if we consider what is being asked of trees in this drought it gives us pause to rethink our approach to providing water to insure that these trees will survive. In some parts of the state oaks are being deprived of water for as long as nine months, in some cases even longer, creating extreme water stress in trees. Stress provides an opportunity for other pests and diseases to expand and further stress the oaks. Ultimately, trees will succumb to the multiple stress impacts brought on by the drought.

Though against all past conventional wisdom we are now suggesting to those concerned and asking about their “fixture” oaks that a once-a-month irrigation be provided during the dry months in an attempt to sustain the trees until the onset of winter rains. Obviously, this can only be considered if one might have water to spare or is not under severe mandatory water rationing.

The once-a-month irrigation should be directed and concentrated below the drip-line of the tree. This is the area directly below the branches. Sufficient water should be provided to insure percolation down to 12-18” below the soil line.

It's important to allow the soil to dry out completely between irrigations to reduce the risk of root diseases. Moderation is the key to this strategy and should only be considered a stop-gap measure until the drought conditions have abated.


By Gregory A Giusti
Author - Past County Director Lake & Mendocino Counties, Advisor:Forests & Wildland Ecology - Retired/ Emeritus Status
By Richard B Standiford
Editor - Cooperative Extension Forest Management Specialist, Emeritus