Here’s an easy way you can help California native wildflowers thrive

California wildflower blooms aren’t expected to be as big this year, but there’s an easy action you could take to help other native plants grow around you.

A new study from researchers at UC Riverside found that raking away thatch — a tan layer of dead plant debris produced by invasive plants like grasses — can be an effective way to increase biodiversity of native plants.

Why it matters

Advyth Ramachandran,  now a doctoral biology student at the University of Colorado Boulder, was a co-lead on the study. He grew up in Northern California with an interest in learning about the plants that make up our grasslands.

“ Almost none of these species are actually indigenous to California,” he said. “There’s been this huge replacement. It was a real shock to me.”

Invasive plants are slowly squeezing out native plants, and could be made worse by the climate crisis. Over the next 100 years, it’s estimated that 66% of the state’s native species will shrink in numbers.

But the mechanism of how that happens has not fully been understood.

On grass, thatch typically shows up at the base of grass blades.

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Courtesy Izhamwong via Wikimedia Commons under CC BY-SA 3.0

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That’s why Ramachandran and a team of students and professors at the university decided to look into it.

“One of the thoughts is that the reason that these invasive species have been able to outcompete the native species and replace them is because these invasive species produce these layers of dead matter," Ramachandran said.

Invasive grasses, such as the commonly used Bermuda grass, are a large producer of this thatch.

He said the idea is that thatch drowns out native species by smothering them — essentially preventing them from getting light, germinating and growing.

What the research showed

Over three years, the team set up multiple plots on a hill at UC Riverside where thatch was raked away in some, and not in others. Then, they measured what kinds of plants grew afterward.

“ What we found was that indeed the plots in which we removed those dead layers of grass had higher biodiversity,” he said.

A raked plot being surveyed for plant biodiversity in March 2022. In this raked plot, the removal of thatch exposed the soil, which is thought to help native wildflowers to grow.

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Courtesy Advyth Ramachandran

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A plot after it was raked to remove thatch in October 2022.

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Courtesy Advyth Ramachandran

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The results pointed to a specific type of increase. While the raked plots did have more types of species present (by a small amount), the real benefit came from how many of the native plants there were overall.

“ Not necessarily new species appeared,” Ramachandran said. “[But] there were more of them. They could grow bigger.”

How you can apply it

Lupinus truncatus, a native wildflower, at the project site in March 2023.

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Courtesy Advyth Ramachandran

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Ramachandran said the research has big implications for restoration efforts and park management, but that it can apply to residences, too.

The changes you see could vary depending on your land, moisture level and location. But it could be easier than hand-weeding non-native plants and safer than using herbicides.

For example, if you have a landscape with invasive grasses that are producing thatch, particularly if it’s not irrigated, raking the litter away could promote the native species if you have ones already there.

“I’ve done it in my garden,” he said.

So come this spring, get ready to rake a leg in exchange for some beautiful native flora.