[T]here’s nothing especially wrong with Wolverton’s 1989 study. Its results “fall right in line with other stuff that’s been measured in the literature.” But taking its results at face value significantly overstates the power of plants, he said. Wolverton measured whether houseplants could remove VOCs from an airtight laboratory environment. But a home is not a hermetic chamber. It has open windows and doors, drafts and leaks, and much more clutter.

Recently, Waring and his colleagues reanalyzed all 195 studies that have examined whether houseplants can filter the air. They found that some types of plants can remove higher amounts of VOCs than others. But once you factor in the effects of working in a large room, none of the plants are able to do much.

Waring told me to imagine a small office, 10 feet by 10 feet by eight feet. “You would have to put 1,000 plants in that office to have the same air-cleaning capacity of just changing over the air once per hour, which is the typical air-exchange rate in an office ventilation system,” he said. That’s 10 plants per square foot of floor space. Even if you chose the most effective type of VOC-filtering plant, you would still need one plant per square foot, Waring said.