The good, bad and ugly truths about LA tumbleweeds and their role in fires

It was Jan. 11 — the first Saturday after the two huge L.A. fires broke out.

The city was thick with haze and smoke; ash was twirling in the air, and somehow, despite it all, our myth-making sunset still shone through.

I was heading home to El Sereno that afternoon, made a turn, and slammed on the brakes.

Tumbleweeds are trippy to look at, but they heighten fire danger in SoCal.

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Fiona Ng

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LAist

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Tumbleweeds, tumbleweeds, tumbleweeds

Fifty to 100 tumbleweeds had parked themselves along Multnomah Street, extending to the hillside above.

Many were over 5-feet-2 inches tall — in short, taller than me.

The street looked like an alien landscape.

My neighborhood isn't the only one to be besieged by these rolling dead plants of unusual size fueled by Santa Ana winds. In 2023, my colleague Yusra Farzan documented giant tumbleweed sightings in a number of Southern California cities.

5-foot tall tumbleweeds gather along the side of a street in El Sereno.

(

Fiona Ng

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LAist

)

A short history

Russian thistles, better known as tumbleweeds, arrived in South Dakota in the 1870s most likely via a shipment of flaxseeds from Russia that was contaminated with the invasive seeds.

"Then those tumbleweeds just spread across the western United States and they've found a great home here in California," said Mark Hoddle, an invasive species expert at UC Riverside.

Yes, it's a living, breathing plant

You can think of the tumbleweed existing in two stages.

First, as a living plant.

When "it's healthy and still alive, it's got, I think, a rather attractive green color to it, but it's very prickly, kind of like a thistle,  but if you have long pants on, you can pretty much push through it OK, and it won't cause too much damage," Hoddle said.

But toward the end of the summer and into early winter, it turns into the post-apocalyptic zombie version we have all come to marvel and chuckle at.

"When the plants finish growing and it dries out and the strong winds come up, the dried up part that's above ground snaps off from the roots. And then as it's tumbling along, it's releasing seeds," Hoddle said.

As many as 200,000 seeds, he said, citing research. From there, the cycle begins all over again — but now in even more places.

"All those seeds need to find is a little patch of moist ground, and then they're pretty much established there for a long time," Hoddle said.

In California, Hoddle added, the weeds thrive on land disturbed by agriculture or off-roading. Those activities create crevices and cracks where seeds can drop in and germinate.

More worrisome is the absence of a natural predator that could check its growth.

"In parts of the native range in Europe, for example, there are insects that feed on [different parts of] these tumbleweeds," he said. "That combined feeding pressure reduces the vigor, or the aggressiveness, of tumbleweeds."

Researchers have long been searching for "natural enemies" to feed on Russian thistles in California, but according to Hoddle, the task has gotten trickier.

That’s because the different types of tumbleweeds that have established themselves here have hybridized — something that's thought to be unlikely to happen in their native habitat.

That means, a new kind of natural enemy might be needed.

" There's been a lot of work going into figuring out, well, you know, where did those tumbleweeds come from?" he said. "Can we possibly find areas back in the native range where those hybrids exist naturally and that the insects have evolved to feed on them?"

And a coalition of scientists from state and federal governments, as well as from academia — like Hoddle, who specializes in locating biological controls to invasive pests — have banded together for the mission because the humble tumbleweed has become such a problem.

"When we have a lot of fires, like we've seen in Southern California recently, these invasive weeds, like tumbleweeds, can really amplify fire risk," Hoddle said, because they provide more fuel for fires to burn hotter.

" They've changed the fire ecology of the state enormously. And that's just one weed. We've got heaps of these weeds," he added.

When I returned to Multnomah Street this week, just a few stragglers remained on the sidewalk, awaiting a breeze and a chance to tumble.