Saving trees in time of drought
02/22/2014 12:00 AM
02/21/2014 6:01 PM
Sacramento likes its status as the “City of Trees.”
We say hello to stately elms and wave at friendly palms. We worry over heritage oaks and nurture weeping cherries.
We love their shade, their fruit, their beauty. And when it comes to sharing our water, trees become our priority.
The worst drought in generations has many homeowners concerned about the oldest – and likely most valuable – plants in their landscapes: trees. It takes a few months to grow a lawn, but many years to grow a mature tree.
“Everybody’s asking about trees,” said sustainable-landscape expert Cheryl Buckwalter, executive director of EcoLandscape California.
Experts at local water districts have been flooded by calls from residents.
“About 70 percent of our (residential) water use is for landscapes,” said Vicki Sacksteder, water resources analyst for the San Juan Water District. “If we ask people to cut back, we need to give them some options.”
Sacksteder remembers California’s killer drought in the 1970s that threatened even unthirsty valley oaks. “Some people just stopped watering,” she said. “A neighbor’s redwood trees died in a matter of months. Then, (those trees) became a fire danger.”
Some issues are rooted in old choices. Trees that were meant to grow in locations with lots of water are forced to cope with urban landscapes; that includes hot spots caused by concrete driveways. Or trees are planted in lawns where they never develop healthy, deep roots due to constant shallow irrigation.
“We have large old sycamore trees lining our street,” said homeowner Robert Meagher of Sacramento. “I have been told these trees do not have ‘tap roots’ and depend on getting large amounts of water from roots in the top few feet of soil. My tree’s roots spread out under my entire front lawn.”
What will happen to the sycamores if the lawns don’t get watered?
“Don’t these trees depend on significant amounts of supplemental landscape irrigation – particularly during droughts – to stay alive?” Meagher asked.
Sycamores are one example of many trees that need a helping human hand during drought. More than 7 million trees are part of the Sacramento region’s urban forest and very few of them grew totally on their own. Historically, the Sacramento region had few native trees except for valley oaks and trees that grew along waterways.
“The vast majority of (our) trees have been planted by hand, not nature,” said Ray Tretheway, executive director of the Sacramento Tree Foundation. “People, businesses and local governments planted these trees to cool summer temperatures, clean the air, shade neighborhoods and save energy. ... This remarkable hand-planted urban forest is a defining feature of our region. But that forest needs water to live.”
The foundation put together drought-minded tips on care of both young and mature trees. It’s not the same for both.
“Young trees benefit most from frequent irrigation,” said arborist Roger Poulson. “Their roots are still developing. They need consistent moisture in the root zone.”
Young trees are at the greatest risk during drought, he said.
“Younger trees that have been in the ground for a year or two haven’t gotten a chance to establish roots widespread and deep,” Poulson said. “The ideal way to irrigate a new tree is like a new lawn.”
Mature trees – those that have been growing for a few years in one spot – benefit from deep infrequent irrigation. This method trains their roots to spread out and down.
The results of shallow watering can be seen vividly after a storm, Buckwalter noted. Battered by wind, huge trees fall down for lack of support; their roots are too weak to hold them up during or after a big storm when the ground may be saturated, too.
“Go out after a windstorm and you’ll see all these trees planted in lawns that fell over,” Poulson said. “Probably 90 percent of those that fell over were because of improper watering.”
This drought has further stressed big trees and leaves them susceptible to disease, pest infestation and other life-threatening danger. It’s not just the tree that can get hurt; falling limbs and trunks also are hazardous to people and property.
“You don’t want to set up trees for failure,” Buckwalter said. “Water trees by hand. Look at the canopy of the tree; that’s important. The roots go out as far as the branches.”
Lawn trees face a combination of challenges. Fed a steady stream of sprinkler water, they’ve grown accustomed to shallow irrigation. They have no need to stretch their roots down or out in search of moisture. But even in abundance, they may not be getting all the water they need.
“They’re always competing with lawn for water,” Buckwalter said. “They’re not getting deep watering from sprinklers. Instead, water them s-l-o-w-l-y with a hose. Let it soak in. Then, take a (soil) probe and see how far the water reaches.”
Ideally, that water should reach down a foot or more.
“Dig a hole,” Poulson said. “Dig deep; at least 18 inches. That’s the root zone (for many trees). If it’s still moist 18 inches deep, the tree will find that water.”
Some trees are just thirstier than others. Birches, coastal redwoods, red maples and magnolias need regular irrigation even in normal rain years. Ornamental flowering trees as well as all fruit trees need deep watering, preferably twice a month.
“It will affect the fruit if there’s no water,” Poulson said. “For example, improper irrigation in citrus will make the fruit very pithy.”
Sycamores can get by on twice-monthly irrigation. “They’re actually pretty tough,” Poulson said. “They grow naturally near stream beds and need some supplemental water, but they’ll survive.”
Coastal redwoods are more problematic.
“I’m seeing more problems with them lately because they’re not getting enough water,” Poulson said. “People think redwoods are drought tolerant because they’re California natives, but they grow (naturally) in a foggy, constantly damp environment near the coast where they get lots of moisture. They need more water than they’re getting in Sacramento.”
Native to the Sierra, incense cedars naturally need less water, he noted. “To be a native in this part of California, you pretty much have to be drought tolerant.”
Many older trees have tapped into the underground water table, Poulson noted. But during drought, wells have drawn off that same resource. As the water table drops, the tree’s roots are unable to reach that moisture. So even trees that usually need no extra water may need some irrigation.
“You need to monitor the situation and stay in tune with your trees,” he said. “Some will get by on practically nothing. A lot of well-established trees will be just fine – as long as the drought doesn’t go on too long.”
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