Air-purifying house plants a potty idea — rather just open a window

Since Nasa published a paper in 1989 claiming that houseplants can soak up pollutants, people have increasingly invested in greenery to clean their air.

But analysis suggest it could take more than 1,000 plants a square metre to gain a benefit any greater than simply opening a couple of windows.

The problem lies in the fact that Nasa conducted its tests in sealed containers that do not mimic the conditions in most people’s homes or offices.

The space agency was primarily concerned about keeping the air fresh for astronauts in biospheres or space stations, and helping to combat “sick building syndrome”.

Nasa found that plants such as English ivy, bamboo, gerbera and peace lilies could remove benzene, formaldehyde and trichloroethylene.

Even today, garden centres recommend the plants for their air-cleaning properties.

However, an evaluation of dozens of studies by Drexel University in Philadelphia found that house plants have little impact at all.

In fact, natural ventilation is better at cleaning the air.

“This has been a common misconception for some time.

“Plants are great, but they don’t actually clean indoor air quickly enough to have an effect on air quality,” Dr Michael Waring, associate professor of architectural and environmental engineering at Drexel’s College of Engineering, said.

The team also calculated the “clean air delivery rate” for plants in the studies they analysed, and found that the rate at which plants dissipated the compounds was well below the usual rate of air exchange caused by the movement of people coming and going, opening doors and windows.

Many of the studies showed a reduction in the concentration of volatile organic compounds over time, which is probably why people have used them to extol the air-purifying virtues of plants.

But the team’s calculations showed it would take up to 312 plants per 0,093m² of floor space to compete with the aircleaning capacity of a building’s air-handling system or a couple of open windows.

In contrast, Nasa’s sealed experiment recommended one pot plant per 9.3m².

Waring said: “This is certainly an example of how scientific findings can be misleading or misinterpreted over time.

“But it’s also a great example of how scientific research should continually re-examine and question findings.”

The research was published in the Journal of Exposure Science and Environmental Epidemiology .