Why Tree of Heaven strikes terror in the hearts of LA gardeners

Despite its exalted namesake, the Tree of Heaven is a legitimate nightmare to control.

The fast-growing tree — up to 1 inch a week in some documented instances, according to botanist John Knapp at The Nature Conservancy — is considered invasive in California and more than 30 other states.

It requires little water and can thrive in the poorest of soil amid conditions of total neglect. But once the tree sets down roots, eradication efforts are Sisyphean — just ask Venice resident Jeremy McCreary, who noticed an unfamiliar tree at the start of the year at his family property in the Sierra foothills near Fresno.

"It's so vibrant green and everything else it's like a dry climate," McCreary said. "It really sticks out. I had never seen it before."

He image-googled the young plant's orange-tipped leaves, which led him to the tree with the divine moniker.

Eight months later, McCreary is still locked in battle with his Tree of Heaven, now at 40 feet tall and growing, which has ruptured the septic system on his family's land. The massive plant has exploded into numerous offshoots, each sprinting for the sun.

Trees of Heaven in Highland Park.

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Fiona Ng

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LAist

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What is Tree of Heaven

A native of China and Taiwan, the Tree of Heaven was introduced to North America in the 1700s and eventually found its way to Philadelphia. By 1840, it was sold as an ornamental and shade tree in nurseries. It fell out of favor in the 1900s, precisely because of how quickly and easily it grew — but not before they were put in the ground all over the East Coast.

"The tree of heaven is considered the fastest growing tree in the world, as far as we know," said Knapp, a senior island scientist at The Nature Conservancy.

This relentless reach for the skies is the quality that lent it its name. Though the tree needs little water, moisture supercharges its growth. In Southern California, Knapp said you won't likely find it overtaking areas like the Angeles National Forest, given its need for the sun. But it can become a problem if it gets near a stream or a river.

"So, you know, the L.A. River, if Tree of Heaven is there, they can disperse easily," he said, adding that since it also suppresses the growth of other plants, Tree of Heaven can crowd out native species in an area.

In the L.A. region, Knapp said it's most commonly found as an "urban tree" — sneaking out of a broken sidewalks or other overlooked nooks and crannies — escaping the detection of unsuspecting Angelenos.

Despite its generous canopy, the tree's root system can cause major damage to sewers, pavements and even building foundations.

"It's not a great street tree," said Knapp.

A tree of heaven found in Highland Park.

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Fiona Ng

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LAist

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Why it's so difficult to kill

Danny Sway, who works with me at LAist, has been grappling with a Tree of Heaven. Sway and his wife live in Pasadena and their Tree of Heaven journey started recently, spurred by the first-ever sighting of the invasive spotted lanternfly in California this year.

As the Sways read more about the bug, they learned that one of its host plants is the Tree of Heaven — which looked an awful lot like something that was growing next to their house.

While gardening one day, Sway cut down the plant, which was already the size of a small tree.

"Within a few weeks or months, it started growing smaller plants within a 10 feet radius all around our yard," said Sway.

It's this whack-a-mole nature that makes the tree so hard to eradicate.

"It spreads by its roots and then sends up new trunks. You might see 20 stems, but that might be a single individual that is just resprouting," said Knapp, The Nature Conservancy scientist. "Cutting them only forces them to grow more."

To rid the tree once and for all, Knapp said you'd need to get to its roots. A process that takes patience, perseverance, and "a herbicide application — pretty much the only way to really get rid of mature plants."

Knapp spent time on Catalina Island for research for his master's thesis about two decades ago. The plant population he helped to control was the Tree of Heaven. About half an acre of it, he said, and it took about two years to clear them out.

Leaves of a Tree of Heaven.

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Fiona Ng

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LAist

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"The way that I've have killed it in the past is a method called 'cut stump,'" said Knapp — by applying an herbicide on the cut itself. "So it doesn't get on the ground and it basically gets translocated down into the roots."

That's what the Sways in Pasadena are looking to do next. Experts recommend consulting with an arborist before trying anything on trees.

As for McCreary, he's working with a botanist to professionally take down the 40-foot giant on his family's property in Central California. Next up is to repair the expensive septic line damage.

After this long saga, McCreary said he couldn't help but see the tree everywhere he goes.

"I've been noticing it a lot in L.A. It's kind of all I see now," McCreary said. "But yeah, if you see it around your property, look into it."

How to identify Tree of Heaven

Don't do anything before you have a positive ID. When in doubt, consult an arborist or botanist for assistance.

The Tree of Heaven bears a close resemblance to trees like the Black Walnut and Sumacs, but according to Knapp:

• Its leaves are smooth on the edges except for a couple bumps, or teeth, that stick out on either side at the base.
• If crunched, the leaves have a "nutty" smell, like "rotten peanut butter."
• Its bark looks like the skin of a cantaloupe.
• Check out this video from Penn State University on how you can learn to identify a Tree of Heaven.