The "What Can I Do?" page of the new Minneapolis climate plan offers immediate steps people can take to cut the pollution super-heating the planet. Switch out gas appliances for electric ones. Take the bus. Eat less meat.
Minneapolis says planting a snake plant will clean your home's air. It won't.
Houseplants have clear benefits, but scrubbing indoor air is not one of them, many scientists say.
August 1, 2023 at 8:51PM
But grow a snake plant at home to filter the air?
That suggestion in the 100-page plan has some researchers shaking their heads. "Unsubstantiated Facebook rumor" and "persistent myth," said two when asked. Another recommended the suggestion be removed.
It turns out the hardy snake plant suffers from an overgrowth of hype. It's a bit of a potted star on the Internet and Facebook, where it's promoted as a top plant for cleaning indoor air: "Snake plants are extremely good air purifiers! Ask NASA!" said one posting from July.
No one disputes the appeal of the snake plant. They're great houseplants. A succulent native of West Africa and possibly part of Asia, sansevieria trifasciata is a member of the asparagus family. Many varieties have tight clusters of swordlike leaves jutting up. It lives for years.
Houseplants have psychological benefits, bringing more nature inside. And snake plants in particular have a long history. In some cultures they're used to treat ailments; in others the fibers have been used to to make baskets, ropes and bowstrings. For some, the plant has cultural significance as a plant that can ward off evil and bring good luck — which humans particularly need now.
It's true that all plants soak up carbon dioxide, the top atmosphere-heating greenhouse gas.
But unless you're willing to live with nearly 700 snake plants, their overall effect on air quality and carbon dioxide is negligible.
The snake plant was among a group of houseplants studied by the University of Georgia, which reported they soak up only about 0.8 grams of carbon a day. That's a small fraction of the amount a person exhales in a day (about 300 grams) or what's emitted by burning a liter of gas (about 640 grams), the study said. It would take 400 plants "to offset a single human." Estimates of how much CO2 humans breathe out vary greatly and can range to more than 1,000 grams.
Much of the current ballyhoo about snake plants seems linked to a 1989 NASA study. With an eye to people being sealed in a space chamber, it studied the ability of more than a dozen houseplants, including the snake plant and gerbera daisies, to remove volatile organic compounds such as benzene and formaldehyde. They plants "demonstrated the potential for improving indoor air quality," it concluded. The study didn't look at carbon dioxide.
The Associated Press ran a story in May correcting a misinterpretation of the NASA study circulating on Facebook about the plants providing lifesaving oxygen.
But pushback actually started much earlier. Just a few years after the 1989 NASA study was published, the U.S. Environmental Protection Agency commented on it at length, according to a 2017 blog by the American Lung Association. It said the small, sealed conditions used don't translate to the real world and you'd need 680 plants stuffed into a typical house to get the pollution reduction rates noted. "This does not seem practical," the EPA official noted.
Researchers at Drexel University in Philadelphia reached similar conclusions. Potted plants have a "negligible impact" on loads of volatile organic compounds in indoor air, they concluded in their published findings, "Potted Plants Do Not Improve Indoor Air Quality," in the Journal of Exposure Science and Environmental Epidemiology in 2020.
They don't do any better at cutting carbon dioxide, said co-author Bryan Cummings, a research scientist in civil architecture and environmental engineering at Drexel. In an interview, he said houseplants just don't meaningfully reduce either volatile organic compounds or carbon dioxide. You'd need hundreds of them in a room to make a dent.
"We need to reforest millions and millions and millions of acres of land to meaningfully affect the climate," he said. "Adding a couple of snake plants in the home, it's not going to be significant.
"There are other ways I would modify your household if you want to be climate conscious," Cummings said. He pointed to switching out gas appliances.
His study made another interesting finding: that it's not the plant itself that's so important in removing volatile organic compounds, but "the microbial community which resides within the rhizosphere/soil system of the plant."
Susan Arnold, an associate professor in the division of Environmental Health Science in the University of Minnesota School of Public Health, agreed that potted plants are not an effective method to cut carbon dioxide.
"I would consider removing that recommendation," she said.
According to the city of Minneapolis, the source of the recommendation was Girma Hassen, chair of the Oromo Culture Institute of Minnesota, who served on the climate plan's steering committee. In an interview, Hassen said he actively worked on the plan for a few years. He said the snake plant has no cultural significance to him. He was responding to information he found doing his own research, he said.
When told about research finding that a few plants don't actually clean indoor air, he provided a 2018 article from the website of a company in India that sells houseplants: "Snake Plant: Everything You Need to Know." That article, like others, refers to the NASA study and calls the snake plant an "Air Purifier Approved by NASA."
He said he stands by his recommendation. "People have plants in their home because those plants clean air in the room," he said. But he acknowledged he's not an expert and the plants aren't a specialty for him.
"Like anybody else, I just learn," he said.
When the city was asked to comment, Patrick Hanlon, deputy commissioner of the Minneapolis Health Department, and Kim Havey, director of sustainability, issued a statement saying that in creating the new city Climate Equity Plan they took suggestions from diverse communities. They said research shows plants are "beneficial for people's well-being" and can improve air quality inside homes.
And since people have to spend more time inside during heat waves, indoor plants help with "climate resiliency," they said.
"The foundational underpinnings of the report have little to do with the suggested strategy on page 81 of placing a snake plant in your home put forward by our friends in the Oromo community," said city Health Department spokesman Scott Wasserman.
He said the climate plan was thoroughly reviewed by a range of experts and stakeholders.
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