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LADWP on Tree Care: Part 2

May 27, 2024

The Buzz has written a lot about trees over the years, so when LADWP held a special webinar last week on “How to Keep Your Trees and Landscape Thriving During the Drought,” we signed up right away…and found the information to be a great summary of various tree topics we’ve covered one at a time over the years, along with some new information.

Yesterday, in the first segment of our two-part coverage of the webinar, we summarized the session’s introductory information on the drought and LADWP’s efforts to conserve water. Today, in part two, we share more specific information on the importance of trees to the city’s water conservation efforts, and how to properly care for trees so they can both survive the drought and help us survive, too.

Also, as Rachel Malarich, Los Angeles City Forest Officer, explained in the webinar, this information is especially key for homeowners…because although the city cares for street trees, and trees in medians, parks, and other public spaces, about 90% of our urban forest lies on private property, including the yards of single family homes. So it’s up to all of us to care for the city’s trees, which one of the webinar’s other speakers, Rachel O’Leary, Executive Director of LADWP’s City Trees, said “are absolutely one of our best defenses against climate change right now.”

Currently, according to City Trees’ O’Leary, there are about 10 million trees in Los Angeles, which constitute one of the most diverse urban forests in the nation. And to more carefully track our trees, she said, the city is currently working on a citywide tree inventory and mapping project, which will make locating and caring for our trees much easier. (One part of this inventory, an interactive map of park and street trees is now available here – – and it’s a great tool for looking up and identifying any specific tree you might be interested in.)

One complicating factor in caring for the city’s trees right now, however, said O’Leary, is that some people think that while we’re cutting back on other kinds of landscape watering during the drought, we should also stop watering our trees. But O’Leary said healthy trees and water conservation actually go “hand in hand,” and for long-term environmental resilience, we absolutely do need to keep planting new trees, and to keep watering and caring for those we already have.

In fact, O’Leary said, trees actually help protect our water supply by providing shade (which helps to lower urban temperatures), capturing and filtering pollutants out of storm water, keeping water from evaporating as quickly, and reducing other kinds of heat effects (including preventing heat-related deaths). So trees are an absolutely critical part of our urban infrastructure, and we need to water and support them in every way we can…especially during the drought.

In addition to their environmental benefits, O’Leary said, trees are also important for the city’s social equity. She noted that the densest, healthiest tree canopies have always been in our wealthiest neighborhoods, while more underprivileged neighborhoods tend to have fewer, or no, trees. And the environmental effects are clear, she said, as illustrated in this series of photographs from National Geographic magazine, moving from from wealthier areas on the northern end of Vermont Ave. toward poorer neighborhoods further south on the same street.

So the city wants all residents to have equal access to trees, and provides several programs for people throughout Los Angeles to acquire new trees, including free tree adoption events, free street trees, and even one program that actually delivers up to seven new shade trees directly to your door for free.

If you do want to plant a new tree, said Cristina Basurto, a certified arborist and City Trees’ Community Organizing Manager, it’s important to start with tree selection – to plant the right tree, in the right place, for the right reason.

Also among the biggest considerations when choosing a tree, Basurto said, are your Sunset Climate Zone (keeping in mind, too, that with global warming, our climate zones are shifting a bit), how much sun and water it will need, and what your soil is like. (Our urban soil, Basurto said, is often very compacted, which affects permeability and water retention.)

Basurto also noted that it’s important to plant new trees at the proper depth – not too deep (burying too much of the trunk base) or too shallow (leaving the roots exposed). A well-planted tree, she said, should have its “shoulders” (roots) below ground, to prevent drying out the tree, and its “neck” (trunk base) above ground, to prevent trunk rot.

Basurto said that when trees are young, it’s important to watch and “listen” and get to know them…and they will tell you what they need.

Also, she said, one good general practice is that new trees should be planted with a cleared basin around the tree, with a raised berm of soil to help hold water.

New trees also need about 3-4 inches of mulch around the root zone, Basurto said, with the area around the trunk left clear, to help preserve moisture and nutrients, prevent weed growth, and protect the roots from extreme temperatures.

At the same time, however, Basurto said it’s important not to use so much mulch that you create a “mulch volcano,” which can cause root rot and other problems.

And, of course, the city of LA also provides free mulch for your trees – see, or scan the QR code below, for details.

Basurto said a healthy mature tree is one with a trunk too big to wrap your hand around, and which can’t be pushed from side to side. But while mature tree care is different from care of young trees, Basurto said it’s not true that mature trees need to be pruned every year to be healthy. In fact, she said, trees should not be pruned more than 20% per year, and you should never “top” a tree, which causes immediate injury to the tree, weakens its growth, and can actually kill it.

Providing further information on watering for mature trees, O’Leary said established trees, 3-5 years old, need less frequent watering than young trees, and some varieties can even go a month between waterings.

But just as with young trees, O’Leary says the process start with observation…and she recommends that people “have morning coffee with your tree,” to watch it carefully and see how it’s doing.

When it is time to water a mature tree, O’Leary said, deep root watering is key, wetting the soil 6-12″ deep all around the root zone (you can check it by probing with a screwdriver or shovel after watering). Also, said O’Leary, infrequent deep watering is actually better than frequent light watering, which can lead to weak roots. But it’s also important not to over water the tree.

O’Leary said there are many good ways to water trees, even during the drought. First, of course, there is hand watering with a hose or bucket, which is still allowed at any time, on any day, and is not subject to the city’s mandated watering schedules. Just pour the water into the berm you’ve created around the tree base, and let it filter down into the soil. In general, apply about 10-15 gallons per watering when using a bucket. (You can also widen the berm over time, to make room for more water as the tree grows.)

Tree watering bags are also helpful for both young and mature trees, said O’Leary, and the bag helps keep water from evaporating as it drains into the soil around the tree’s root zone.

Soaker hoses, too, can be used at any time, even during the drought. The porous material of the soaker allows water to seep out slowly along the length of the hose, and – like the methods above – targets the water delivery and prevents evaporation better than sprinklers.

Similarly, you can also make your own DIY drip-irrigation device by poking holes in the bottom of a 5-gallon plastic bucket, then filling the bucket and placing it inside the tree berm to drain slowly by itself.

Finally, there are several options for obtaining water for your trees, in addition to your garden hose or sprinkler system. For example, you can collect rain water (especially at this time of year) in a rain barrel or trash can. And when it’s not raining, you can put a bucket in your shower to collect unused water as it’s warming up before you step in.

Also, as mentioned in yesterday’s story about the DWP webinar, the city operates several recycled water fill stations, where you can bring your own containers to fill with water for landscaping and other non-drinking uses. (The closest of these to our area is at the LA Zoo.)

For more information, you can download the free Dashboard Earth app from City Plants and other community sponsors. The app will help you learn more about tree care during the drought, register your existing trees, learn when and how to water them, connect to resources like free mulch…and much, much more.

Finally, as the introduction to the app says, “Hundreds of millions of trees have died during previous drought seasons” and “we can’t let it happen again.” So yes, please do keep watering your trees during the drought – it actually helps protect our endangered water supply.

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