Air-purifying plants sound like something out of science fiction, so maybe it shouldn’t come as a surprise that we know about them thanks to a NASA study. In the 1980s, a team led by Bill Wolverton, PhD, determined that plants are capable of removing volatile organic compounds from sealed environments. Obviously, those findings were important for aerospace professionals—a typical spacecraft has a significant amount of weird compounds bouncing around inside of it—but the NASA Clean Air Study also had important implications for typical American households. We decided to look into the practical side of the science: Can houseplants really improve indoor air quality, and if so, to what extent? Are certain plants better than others?
How Volatile Organic Compounds Affect Indoor Air Quality
First, let’s take a quick step back: Volatile organic compounds (better known as VOCs) are a problem because they’re thought to cause various ill effects, including fatigue, allergic skin reactions, headaches, nausea, and even serious problems like central nervous system damage. Some are known carcinogens, per the Environmental Protection Agency. There’s even evidence that VOCs cause something called sick building syndrome, which occurs when the occupants of a building become mysteriously ill. Unfortunately, we basically invite these pollutants into our homes: VOCs can be emitted by certain paints, flooring, furniture, computer printers, aerosol sprays, and hobby supplies. So, how do air-purifying plants get rid of VOCs? Do they chow down on them, Little Shop of Horrors style? (Not quite.) To find out how air-purifying plants do their jobs, we reached out to Wolverton, who’s continued to research plants’ effect on indoor air quality since his groundbreaking work with NASA. He’s also written several books, including his most recent, Plants: Why You Can’t Live Without Them. “Plant leaves produce negative ions as they emit water vapor during the process of transpiration,” Wolverton tells us via email. “Plants with the highest transpiration rates produce the most negative ions. Negative ions have the ability to destroy airborne molds and bacteria. Negative ions are charged particles that attract dust to their leaves. This is why dust often accumulates on their leaves.” “So, in essence, the negative ions are pulling dust particles to the leaves and reducing the amount of dust particles that are suspended in the air,” he continues. “This same mechanism assists in the removal of VOCs from the air. The transpiration process pulls air down to the plant roots. VOCs in the air are brought down to the root zone, where microbes biologically break them down and utilize them as a source of food for themselves and their host plant.” We’d love to simplify that as “Yes, plants chow down on pollutants, Little Shop of Horrors style,” but it’s a bit more complicated than that. There is some evidence that micro-organisms surrounding the plants do most of the heavy lifting. In any case, plants do seem to eliminate VOCs, but scientists disagree as to the extent of the effect. Majbrit Dela Cruz of the University of Copenhagen has also studied how potted plants remove VOCs. “In our group, we have not investigated homes or offices, but there are a few other studies that show that plants remove VOCs in real-life conditions,” Dela Cruz tells us. “Unfortunately, there is not much research that has investigated removal of VOCs by plants in real-life conditions. At the moment, I would say that it’s impossible to make a general statement to what extent plants can improve our air.” Wolverton, on the other hand, strongly believes that houseplants can affect indoor air quality (IAQ), and not simply by producing oxygen. “Most homes do not use mechanical ventilation, and interior plants can be very effective in improving IAQ in energy-efficient homes,” he writes. “While at NASA, we conducted a study in a tightly sealed structure that we termed the ‘Biohome.’” “Through sophisticated analytical instrumentation, we showed that interior plants could remove most of the chemicals within this structure that was laden with indoor air pollutants.”
Are certain air-purifying plants better than others?
All of that research is fascinating, but it doesn’t really help us choose between a Boston fern and a peace lily. “I’m often asked the question Which plants should I choose for my home and how many?” says Dela Cruz, shortly after we asked her those exact questions in that exact order. “This is not possible to answer.” To be clear, Dela Cruz does believe that plants improve air quality, but she didn’t want to recommend specific plants, simply because she believes that researchers need to study the issue in greater detail before offering advice. “People wonder how difficult it can be to quickly test a lot of plants,” she writes. “It may not be difficult to screen a number of plants to see if they have a potential to remove a few compounds, but to investigate if they can remove hundreds of compounds over a long time period (which is what they should be able to do in real-life conditions) will take a lot of time.” Wolverton, however, isn’t shy about making recommendations. His company’s website notes formaldehyde (a common and potentially harmful VOC) removal rates for a number of different potted plants in potting soil, so if you’re looking for specific air-purifying plants, these are the plants Wolverton recommends based on his research.
Boston Fern (Nephrolepis exaltata Bostoniensis)
The Boston fern showed the highest removal rates in his study: 1,863 micrograms per hour. While you probably won’t be measuring micrograms of VOCs, it’s good to know that this easy-to-care-for fern is at the top of Wolverton’s list. If you get one, don’t forget to keep this baby humid—it thrives in damp soil!
Dwarf Date Palm (Phoenix roebelenii)
The dwarf date palm comes in second in Wolverton’s tests, with a removal rate of 1,385 micrograms per hour. If you’re feeling tropical vibes, this is the plant for you. It’s an easy plant to love, but make sure you’ve got space: They can grow to between 6 and 12 feet tall.
Bamboo Palm (Chamaedorea seifrizii)
If you’ve got a low-light space, the bamboo palm might be your best bet for air-purifying plants. Wolverton notes that this plant removes 1,350 micrograms of formaldehyde per hour. Though it’ll get tall like the dwarf date palm, it’s a little more low maintenance.
Dracaena Janet Craig (Dracaena deremensis ‘Janet Craig’)
The dracaena Janet Craig may be the perfect houseplant: It’s easy to care for (sensing a theme?), its colors are beautiful, and Wolverton says it removes 1,328 micrograms per hour. Get yourself a Janet.
English Ivy (Hedera helix)
We all know English ivy. Though it’s usually grown outside, give it some bright light and something to climb up (or down), and it’ll be perfectly happy purifying the air of your abode. Wolverton notes that its removal rate is 1,120 micrograms per hour, too.
Weeping Fig (Ficus benjamina)
It’s a tree! Inside the house! And though it has a sad name, the weeping fig will bring joy (and a decrease of 940 micrograms of formaldehyde an hour) into your house. Though its natural habitat is the rainforest, it’ll work well in your house too—provided that you leave it alone.
Peace Lily (Spathiphyllum ‘Clevelandii’)
Not quite a gardener? Start with a peace lily. It’s not actually a lily, it’s hard to kill, and it’s pretty. Plus it’s on the NASA study’s list and Wolverton’s list as a household air-cleaning plant, thanks to its removal rate of 939 micrograms per hour.
Areca Palm (Dypsis lutescens)
You haven’t seen a plant on Instagram if you haven’t seen an areca palm on Instagram. This big palm, with a 948 microgram removal rate, will cover up a bare corner or wide wall easily. They can live for up to 10 years, so be ready to commit. (Wolverton does note on his site that these removal numbers come from chamber-sealed studies, not in a real house where “conditions could vary significantly.” So he recommends doubling up if you’re looking to buy one—or more!—of these air-purifying plants.) Regardless of contradictory research about VOC removal, having plants within the home is a great way to reduce carbon dioxide and increase the amount of oxygen, which is beneficial on its own. If you’re looking to get started, Wolverton writes on his website, “I recommend at least two good-sized plants per 100 square feet of space within a home. Of course,” he notes, “if the homeowner can maintain more plants, then it is even better.” Plant ladies, unite! When choosing any new air-purifying plant, keep these tips in mind:
Remember that some plants are toxic to pets and humans.
According to the National Resource Center for Health and Safety in Child Care, examples include the morning glory, lily of the valley, iris, foxglove, and hyacinth. Flowering plants, in other words, tend to be poisonous, whereas plants like the Boston fern, jade plant, and snake plant (ironically) tend to be safe. Research any new plant before bringing it into your home, regardless of how cute it looks on your kitchen table.
Suit your houseplants to your lifestyle.
Your new plant can’t purify the air if it’s dead. Some of the HealthyWay crew aren’t natural green thumbs or used to sticking to watering schedules, which is why we picked up a cast iron plant (Aspidistra elatior) in our office; it got its name because it’s incredibly tough! Other hardy options include the jade plant and spider plant. Boston ferns aren’t too tough to care for, either, but they require plenty of light and high humidity.
Finally, if you’ve got allergies, avoid blooming plants, as they can produce pollen.
Wolverton also suggests taking a few extra steps to eliminate standing water. “It is best to cover the potting soil with a layer of porous material, [for instance] aquarium gravel, hydroculture pebbles, etc.,” he writes. “This allows the surface of the plant container to stay dry, and therefore, [it] will not grow mold.” This might also boost the plant’s air purifying powers to some extent. “I recommend that people with allergy sensitivities grow their plants in hydroculture,” Wolverton writes. “In hydroculture, plants are grown in pebbles instead of soil and the container is sealed. Therefore, you eliminate the problem of standing water in the drain tray when using potting soil. Our studies show that plants grown in hydroculture are more effective in removing VOCs because the air can more easily travel to the plant’s roots through pebbles than in compacted soil.” If you’re concerned about VOCs, the best way to keep them out of your home is to stop them from entering in the first place. Choose low- or no-VOC paints, renovate with low-VOC construction materials, and buy higher quality furniture (secondhand where possible—it’s better for the environment, and antiques beat IKEA any day). With that said, a few houseplants will certainly improve air quality, and although the extent of the effect is debatable, we’re pretty happy with our cast iron plants and Boston ferns. Plus, we get to tell our houseguests about “biofiltration.” That’s certainly worth a trip to the gardening center.