In the world of wildfires, there are basically two kinds of ash: the good kind from burned vegetation that enriches the soil and the very bad ash from urban wildfires that’s created when everyday items like plastics, electronics, couches and tires burn along with people’s offices, homes and stores.

“Ash from a chaparral [vegetation] fire is clean; it contains nutrients like phosphorous and potassium that can be beneficial,” said Garn Wallace, a biochemist and soil scientist whose business, Wallace Laboratories in El Segundo, has been testing California soils since 1990. “But ash from a home that burned risks having heavy metals that came from the construction materials or were used in the paint or furniture. And ash from that house could be toxic.”

Therefore, multiple federal, state and local agencies, including the federal Environmental Protection Agency and state Department of Toxic Substances Control, are working to clean up more than 16,000 homes and other structures in Pacific Palisades and Altadena and have been tasked with assessing, removing and disposing of hazardous materials such as ash around those burned-up structures.

Because of the danger from toxins, Los Angeles County has prohibited residents from cleaning up properties that were damaged or destroyed in burn areas “until a hazardous materials inspection is completed by an approved government agency.”

But what about residents whose homes didn’t burn but whose yards and gardens still got a coating of ash? At present, there don’t appear to be any cleanup programs or prohibitions for properties with ash contamination but no other fire damage. In other words, it appears you’ll have to handle those kinds of cleanups yourself.

It’s best to carefully corral and dispose of ash on your property to keep your household safe. Pets can track potentially toxic ash into the house or lick it off their paws; children can get it on their hands and clothes and even in their mouths. And every time you work in your garden you’re potentially exposing yourself to toxins in the ash such as heavy metals including lead or VOCs (volatile organic compounds) like benzene, a carcinogen that can create serious health issues after long-term exposure.

With this in mind, here are answers from health, soil and gardening experts who’ve studied the subject when it comes to navigating the task of cleaning up ash and other toxins.

How can I protect myself when I work around ash from recent L.A.-area wildfires?

Whether you work with a professional to clean up your yard or take on the matter yourself, you need to stay safe.

At a minimum, wear an N95 mask and sturdy gloves before working in a yard doused with ash to protect yourself from inhaling or absorbing potentially toxic metals or chemicals. Safer still is wearing safety goggles, long pants, long-sleeve shirts and boots to minimize contact with eyes and skin. Remove your boots and clothing at the door and clean them thoroughly so you don’t track ash into the house or leave it on furniture.

Since young children tend to put everything in their mouths, it’s best to keep them and their toys inside until the ash has been removed. The same goes for pets; keep them indoors as much as possible, and when they do go outside, be sure to wipe off their feet and coats so they don’t track it inside or ingest it by licking their paws.

Do everything to keep the ash from going airborne

The Los Angeles County Department of Public Health issued an emergency order Jan. 10 prohibiting the use of leaf blowers and other power air blowers countywide. That order was revised Jan. 23 to prohibit use of those types of blowers in Palisades and Eaton wildfire perimeter areas only.

However, the county’s health department still recommends that people outside the burn areas consider alternatives to the use of power air blowers for removing ash, such as “gentle sweeping followed by wet mopping or HEPA vacuums” so the particles don’t become airborne and easily inhaled.

What’s the best way to remove ash from yards in non-fire areas?

If you’re dealing with ash problems outside the burn areas, researchers recommend dampening the ash first and then either gently sweeping or shoveling as much as possible into plastic bags that can be tightly closed and put in the garbage. Remember to wear personal protective gear while doing this so you don’t inhale the dust.

Gardeners with raised beds who had a lot of urban wildfire ash should consider removing the top six inches of soil as well and disposing of it in plastic bags in the trash. Then add fresh soil to the beds, Wallace said.

Do not put the ash or contaminated soil into green bins or compost piles because it could contain toxins, or at the very least, high alkalinity that could be harmful to plants. Also, make sure the ash is tightly contained in a plastic bag — even double-bagged — so it can’t spill out of the trash and become airborne.

If you have a shop vac with a HEPA filter that can suck — not blow — the ash into a plastic bag, you can try using that on impermeable surfaces such as driveways or patios, or even in garden beds. Just make sure the vacuum doesn’t send the ash flying.

Is it safe for me to eat produce from a garden that was covered in ash?

Yes, as long as you can remove the ash by washing the produce thoroughly, according to Dr. Gina Solomon, chief of the Division of Occupational, Environmental and Climate Medicine at UC San Francisco.

Researchers at UC Cooperative Extension of Sonoma County, who studied the effects of wildfire on soil and produce, recommend removing outer leaves and peels in addition to giving any ash-covered produce a thorough washing.

After a series of urban wildfires in 2017, UC Cooperative Extension of Sonoma County studied the effects of smoke on soil, produce, chickens and egg production in areas that were not adjacent to burned structures.

Dense gray wildfire smoke from the Palisades and Eaton fires blanketed downtown Los Angeles as well as Los Angeles County on Jan. 9, prompting school closures and triggering air quality advisories across the region.

(Allen J. Schaben / Los Angeles Times)

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The department created a webinar and website about its findings, concluding that there was “low concern of health impacts from ingesting produce exposed to the Santa Rosa urban wildfire smoke of 2017.” They determined that the benefits of growing and eating fresh leafy greens such as kale outweighed any long-term cancer risk.

The Sonoma County researchers also concluded that produce must be thoroughly washed before it’s eaten. This is particularly important for produce like root vegetables, which have direct contact with the ground. Peeling vegetables such as carrots or potatoes and removing outer leaves of lettuce or spinach will help remove any contaminants that might be clinging to the food.

Gardeners can soak their produce in a solution of one cup white vinegar to nine cups clean water to better remove the ash and then rinse the produce thoroughly under running water to remove the vinegar.

If the food is too delicate for a good washing — say, tender lettuce leaves — “then it might be time to discard that produce “and take a trip to the farmer’s market or grocery store [to buy a replacement],” Solomon said, especially for people who are more vulnerable to toxins such as children, people who are pregnant or people with underlying health issues.

Wallace had one proviso: If the fruit or vegetables have been scorched or damaged by fire, it’s possible toxins or heavy metals have embedded in the food, and it should be discarded. “If the leaves are still green and the plant looks healthy, the produce should be fine,” even if it’s dusted with ash, “but if it’s scorched, it could contain metals that won’t wash off,” he said.

Don’t eat fruits and vegetables that have been scorched in the urban wildfires, such as these lemons roasted in the Eaton fire, because they could be contaminated by toxic smoke, biochemist Garn Wallace said.

(Jeanette Marantos / Los Angeles Times)

How will ash affect my plants?

Ashy coatings can stunt growth by blocking sunlight to the plant. Wash ash off your plants with a garden hose as soon as possible or hope for a good rain to keep the plants healthy. (On a side note, Solomon said ash is corrosive, so it’s a good idea to rinse it off your vehicles as soon as possible too to keep it from damaging the finish.)

When washing off your plants, try to keep the water on your soil. That might add more contaminants to your soil, but it’s better than spreading the toxins by flushing it down drains or gutters, according to the South Coast Air Quality Management District.

Is my soil safe for planting a new vegetable garden?

This question is harder to answer, said Wallace, whose lab is one of the few in Southern California that tests for heavy metals in soil as well as nutrients and alkaline levels. (Labs that perform similar tests include Alluvial Soil Lab in Anaheim, Pinnacle Laboratory in Lawndale, Vert Environmental in Placentia, LA Testing in Huntington Beach and Babcock Laboratories in Riverside.)

A light dusting of ash probably won’t do much damage to your soil, said Wallace, but a thick layer could raise the alkaline levels above eight, making it difficult for plants to grow, and lace the soil with heavy metals such as lead. In that case, the safest bet is to test your soil to see if its PH is too high (that means an alkalinity over eight), or if it’s tainted with contaminants.

Test prices range between $100 and $200, depending on what the tests entail. Wallace Laboratories, for instance, charges $100 to test for PH levels, salinity, fertility (nutrients in the soil) and trace heavy metals such as lead and arsenic. One two- to three-cup sample of ash can provide information about soil contamination for an entire neighborhood, Wallace said. “The results should not vary much from house to house,” he said.

Wallace said officials are most likely to find high levels of lead in the ash because many of the buildings that burned, especially in the Eaton fire, were old enough to have used lead-based paints.

Like most large cities, many parts of Los Angeles already have issues with lead contamination in the soil, he said. “Up until the late 1950s, the city had people incinerate their trash in their backyard. Every older home in West L.A. has an incinerator footprint where it burned trash, and it’s full of lead,” Wallace said. Also, lead was used in paints and gasoline for automobiles until the 1970s.

The bad news about lead is that it binds to soil particles, he said. “It will not wash away.” The hopeful news is that lead doesn’t move much, he said. It tends to stay near the surface, in the top six inches of the soil, so it’s relatively easy to remove.

Wallace said he tested his soil when he purchased his house in Westwood many decades ago and discovered it had lead contamination. He had hired contractors to install a swimming pool. But he instructed them to first scrape about six inches of soil off his entire yard and dispose of it, then dig an additional two feet in the pool area and use that soil to create planting beds around his yard.

He also regularly adds compost to his planting beds, he said, because studies have shown that those organic materials can dilute lead in the soil.

Tim Becker, horticulture director for the Theodore Payne Foundation, said he tested the soil in his West Adams yard a few years ago and discovered it had lead concentrations of around 65 parts per million, near the state limit of 80 parts per million. But after researching lead contamination, he decided to go ahead and plant some vegetables.

Wildfire smoke from the Palisades and Eaton fires blanketed Los Angeles County with soot and ash, as seen from the Kenneth Hahn State Recreational Area in Ladera Heights on Jan. 8.

(Allen J. Schaben / Los Angeles Times)

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Research such as this 2016 study by the University of Washington indicates the risk of lead poisoning is low in urban gardens because, with the exception of root vegetables, plants take little lead into their stems and leaves. “Runner beans, tomatoes, peppers, cucumbers … those things are still safe to eat,” Becker said. “But I don’t plant root vegetables like carrots or beets, nothing could cause cross contamination of the soil or consuming soil directly.”

Becker said his bigger concern is about children playing in contaminated soil. “Consumption of soil [by children] is the biggest risk for lead,” he said. “You have to do your homework and decide what’s right for you. You can always raise food in potting soil in containers or raised beds.”

What else can I do to improve my soil quality?

Research has shown that certain plants such as yarrow, mugwort and sunflowers can draw heavy metals and other contaminants from the soil in a process known as phytoremediation.

After all this oppressive smoke and gray ash, this sounds like an easy and excellent balm for many local communities. Tall rows of cheerful sunflowers can provide badly needed food and refuge for insects and birds while magically and majestically improving the soil.

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Published January 25, 2025 3:00 PM PST