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Wednesday, January 16 , 2019, 5:52 pm | Rain Fog/Mist 60º


Joan Bolton: How to Keep Trees Healthy During Drought

Forgo lawns and water-hogging plants, but give oaks and other native trees some winter water

Make like rain and start irrigating your trees.

The two gentle waves of rain that fell this week have been wonderful for washing off dust, freshening the air and moistening the soil. But they only put a dent in a water deficit that’s been building for the past few years. 2013 was one of our driest years on record and both Gov. Jerry Brown and Santa Barbara County have declared a drought emergency.

So why suggest upping your irrigation if we’ve had a little rain, plus we’re in a drought?

Because there’s so much to lose if you lose your trees.

Trees provide immense value to our landscapes. As foundation plants, they supply structure, shade and wildlife habitat, and take considerable years to grow. They are far more deserving of our precious water than thirsty lawns and smaller plants that are easier to replace.

If you lose a 30-year-old tree to drought, you’ll have to wait another 30 years for a new one to grow the same size.

And given the current weather outlook, deep-irrigating your trees over the next few months is the best way to keep them healthy and head off drought stress, especially for our majestic coast live oaks.

If you use a sprinkler to soak your trees, run it slowly, and pull it out toward the edge of the canopy so the water doesn’t strike the trunk. (Joan S. Bolton photo)

“We’re in our third year of much lower than average rainfall,” said Heather Scheck, plant pathologist with Santa Barbara County Agriculture and Weights & Measures. “I already see signs throughout the South County that trees are seriously stressed.”

Those signs include smaller canopies; dry, twiggy branch tips; and leaves that have lost their sheen, are fewer in number and are steadily dropping. Ordinarily, coast live oaks push out most of their growth over winter, then go dormant during summer.

But the drought is restricting their ability to produce new leaves and flowers, which leaves them more susceptible to pest infestations and disease.

Oaks and other mature trees that don’t ordinarily get irrigated face the greatest threat.

What to Do

To see whether your trees are faltering, Scheck advises standing beneath each tree and looking up.

“Do you see a lot of blue sky?” she asked. “If it’s in your own yard, have you done any supplemental watering or has it only had rainfall as irrigation?”

Yet even if you don’t see signs of stress, it’s important to start watering.

“Now is the natural time for the trees to be receiving water as precipitation,” Scheck said. “Ideally, you would imitate natural rainfall as naturally as possible.”

The dead cluster on the left isn’t of much concern because coast live oaks do naturally shed leaves, but the crispy edges on the green leaves in the center indicate the tree is already beginning to suffer. (Joan S. Bolton photo)

Loop a soaker hose around the tree, as far from the trunk as it will reach. That ensures the best coverage throughout the root zone, which extends to the edge of the canopy and beyond. Or use a small, whirly sprinkler in the morning when the air is still, and move it to different spots around the tree every half-hour or so.

Apply the water slowly. If there’s too much pressure, the water may run off rather than penetrate the top layer of earth or even a thick layer of mulch. Water for at least an hour. Wait a few hours or until the next morning, then dig around in the zone to see how deep and far the water has soaked in.

Scheck advises irrigating long enough that the water seeps at least a foot or two into the soil.

“A general rule is that 1 inch of water will penetrate 12 inches of soil,” she said. “But that totally depends on your soil type. The goal is to go deep.

“If you do it too fast, they don’t get the benefit. All we’re trying to do is replace the missing rain, trying to make up what’s missing, not go over.”

She noted that soaking trees is not at all like watering grass. Instead of frequent, shallow cycles, trees prefer deep watering every few weeks. Also, don’t bother to spray the leaves. The water should be directed at the roots, Scheck said.

If you’ve been raking away leaves from beneath your oaks, stop immediately. That loose, thick layer of leaves is marvelous mulch that keeps the soil surface cool and holds in moisture. If you don’t have several inches of build-up already, apply 2 two 3 inches of loose, organic material as soon as possible. Just don’t pile up the mulch against the trunk, as wet mulch against the bark can lead to disease.

What's at Risk

Trees that lie beyond the reach of our drip systems and sprinklers, instead relying on winter rains to quench their thirst, face the greatest peril.

But folks whose landscapes are filled with native and Mediterranean plants and turned off their irrigation last fall might want to deep-soak their plants a few times, too. As might people who put in new plants last fall and have patiently waited for winter rains to water them in.

Hydrating those plants now, at the time of year when they’re programmed to grow, should increase their vigor and enhance their ability to survive voluntary — or mandatory — water restrictions later on.

Likewise, the county is working to shore up its street trees.

Udy Loza, certified arborist for the county Public Works Transportation Division, said he’s ordering several hundred “water gator” bags for young street trees that have no source of irrigation other than rainfall.

The bags, which look like rugged trash sacks, typically hold about 20 gallons of water. They’re pocked with holes that slowly release the water within the trees’ root zones to give them a good, deep soak.

“Up until this last year and a half, we haven’t had a problem,” Loza said. “(Now) we’re really trying to ramp up our watering so we don’t lose our trees ... The public can expect to see the gators over the next month or so.”

Additional Steps

With voluntary water cutbacks of 20 percent now in place countywide, some folks may question why anyone would advise opening the tap even wider.

But stopping watering entirely, without any thought as to the future needs of your plants, may not be the wisest course of action.

Instead, set priorities as to which plants in your landscape are most important. As permanent fixtures that provide long-term beauty, shade, cooling, habitat for wildlife and protect the watershed, trees typically top the list.

Then take steps to ensure the health of your choices. Heavily mulch whatever those are, and water them carefully. Drip irrigation is often the most efficient method, since it applies water slowly, evenly and directly to a targeted area.

To get through the drought, don’t skimp on the “bones” of your landscape.

Instead, let your lawn go dry, along with water guzzlers and other plants that can be most easily replaced when rains do return.

Fill the new gaps with several inches of mulch to prevent the soil from cracking, to dissuade weeds from taking hold and to create a better look than bare dirt.

If you use organic material, such as wood chips, shredded wood or bark nuggets, put the mulch right on the soil. However, if you mulch with gravel, first lay down landscape fabric — not black plastic.

Landscape fabric is porous. It allows moisture and oxygen to reach the earth, but separates the gravel from the soil. Without it, in a few years the dirt is likely to come up through the gravel, the gravel is likely to get smooshed into the dirt, and you’re likely to end up with a gritty mess.

— Joan S. Bolton is a local garden writer, garden coach and garden designer who specializes in colorful, water-conserving gardens. You may contact her through her website, www.santabarbaragardens.com, or email her at .(JavaScript must be enabled to view this email address). Click here for previous columns. The opinions expressed are her own.

To see whether your trees are faltering, stand beneath each one and look up. If you see a lot of blue sky, your oaks may be under stress and will benefit from deep watering. (Joan S. Bolton photo)

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