‘A forest on caffeine’? How coffee can help forests grow faster

Waste left over from the coffee-making process can jolt destroyed forests back to life.

Just like us, forests move faster with a little coffee in their system.

A recent experiment tested whether coffee pulp, a leftover of the coffee growing process, could help bring Costa Rica’s rainforests back to life. Researchers from the University of Hawai'i at Manoa tested two plots to see how the coffee waste would affect deforested land, covering one parcel of grass with about 20 inches of the pulp and leaving the other untouched.

At each site, land had been exploited for years, either to grow coffee or raise cattle, and was eventually abandoned. It was dominated by invasive grasses, primarily an African species called palisade grass, used to feed grazing livestock. The grass can reach 16 feet tall when not trimmed by grazing animals, preventing native rainforests from easily regrowing.

After two years, the plot of land given a boost from coffee showed a dramatic improvement. Eighty percent of the plot was covered by young tree canopy, some trees already 15 feet—including tropical species that can grow as tall as 60 feet—versus just 20 percent in the untreated plot. In the coffee-fueled plot, trees were also four times taller on average, soil samples were more nutrient-rich, and invasive grasses had been eliminated.

The results were published in the journal Ecological Solutions and Evidence.

Not only does it give coffee producers a sustainable way to dispose of their waste, she says, but it also speeds up the timeline to bring back destroyed forests.

“It’s an amazing win-win situation,” says Rebecca Cole, a study author and ecologist from the University of Hawai'i at Manoa. “It takes tropical forest hundreds of years to grow back. To have [such] tall trees in only two years is really spectacular.”

More research needs to be done, Cole acknowledges, to understand the long-term impacts of coffee pulp and whether it causes any unforeseen pollution.

Still, says Cole, “This really was like a forest on caffeine. I think it’s really promising.”

Looking for a win-win 

Coffee beans are the seeds of a fruit called a coffee cherry that, when picked, looks like a bright red or yellow cherry. To get coffee beans, producers remove the fruit’s skin, pulp, and other filmy bits. They then dry and roast the remains to make the grounds that end up in your morning cup. Approximately half the weight of a coffee harvest will end up as waste.

In Costa Rica, says Rakan Zahawi, a study author and director of the Lyon Arboretum at the University of Hawai’i at Manoa, coffee producers typically take all that leftover coffee residue to storage lots where it’s left to decompose.

In the early 2000s, Zahawi visited a similar restoration project using orange peels.

“The difference was night and day,” he says of forests treated with oranges and those left untouched, “There was a huge difference.”

The idea stuck with him when he began working in Costa Rica and took notice of the waste generated by the country’s large coffee industry. If the excess coffee pulp could be put to good use somehow, Cole and Zahawi thought, everyone involved—the coffee producers, land owners, and environmentalists—could benefit.

“Essentially it’s a major waste product that’s expensive to process, and they give it away for free,” says Cole. Rather than paying for the waste to be composted and stored, the only cost to the researchers was renting dump trucks to shuttle the pulp.

How and why it works 

The idea works like this: spread a foot and a half of the coffee pulp on an area covered in pasture grasses and the foliage underneath will smother and cook until it’s asphyxiated, dies, and decomposes.

“You essentially kill all the roots and rhizomes of the grasses,” says Zahawi.

Zahawi and Cole found that as the decomposed remains of the grasses mix with the coffee’s nutrient-rich layer, it creates a fertile soil. That, in turn, attracts insects, which attracts birds, who then drop seeds into the plot, as does the wind.

Then comes the rebirth.

“It looks like a mess for the first two or three years, and then there’s this explosion of new plants coming in,” says Zahawi. “It’s so nutrient rich they’re sort of growing on steroids.”

The key, they found, was to pile on the pulp—using a thick enough layer of pulp in an area flat enough for it not to wash away, and in a climate with a dry period that allowed the coffee to really bake. Essentially, it became like a very successful compost heap.

“If you stick your hand in this gook, it’s really hot—not scalding but hot enough to smother [the grass],” says Zahawi.

A plastic tarp spread across a field and pinned down by weights would also kill the grasses. But “then you have all this plastic waste,” says Zahawi. And new, fertile soil would still need  to be brought in to attract new plants.

Cole says the most common way to restore forests is to plant trees. But compared to just dumping coffee byproduct and letting nature do the planting, it’s labor intensive and expensive.

“I was kind of skeptical it was going to work. I thought we would just have a greener patch of grass,” she says. Instead, they got the beginnings of a new rainforest.

Roadblocks and needed research

While Cole and Zahawi’s experiment with coffee pulp successfully jump-started forest growth, there are downsides.

“Coffee pulp is really stinky,” says Cole, who was raised on a Costa Rican coffee farm. “I grew up with the smell but a lot of people find it pretty offensive.” 

It also attracts a lot of flies and other insects that, despite attracting seed-dispersing birds, are pests for nearby humans.

“There’s also some concern that it will have negative effects on watersheds. There can be some contamination,” says Cole. Coffee pulp contains nutrients like nitrogen and phosphorus that can negatively impact streams and lakes, causing excess algae growth, for example. The pulp may also contain traces of pesticides used during production.

While this experiment was carried out away from water sources, Cole says their future research will look at the potential impact on surrounding areas.

Previous work using orange peels to regrow forests in Costa Rica was met with some backlash. When orange juice maker Del Oro began a partnership with a local protected area to spread truckloads of peels on former cattle pasture, its local competitor, TicoFrut, alleged the program was simply a way to dump waste. The program was stopped by Costa Rican authorities, who sided with the competing juice company.

A promising future for forests?

Dan Janzen and Winnie Hallwachs, a married team of tropical ecologists at the University of Pennsylvania, weren’t surprised by the ecological success of Cole and Zahawi’s reforestation experiment; Janzen forged the relationship between Del Oro and the protected area in 1996 for the same purpose and introduced Zahawi to the concept.

Two decades ago, he saw similar success.

Six months after the orange peels were distributed, Janzen said the small one-hectare plot “looked and smelled horrible.”

“[One and a half] years later it was all gone, and in its place were no invasive African pasture grasses, but a marvelous species-rich patch of broadleaf plants growing from deep black loam soil. Basically, we had fertilized the place very intensively. We were sold,” Janzen writes over email.

He thinks coffee pulp may escape the same fate as the failed orange peel project, saying it’s “less tangled in thorny political issues,” and grown by more small producers rather than two large competing companies.

In addition to researching the long-term impacts, Cole is interested in testing other agricultural by-products. As long as the crop waste is nutrient-rich and not harmful to human health, she would expect similar results.

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