Open a window, keep the plant
Houseplants are often sold as air cleaners. A review of 30 years of studies found you would need hundreds of them to match an open window.
A plant on the windowsill is a good thing. It is just not an air purifier.
Where the idea came from
In 1989 NASA tested plants in small sealed boxes. They put one chemical into the box and measured how fast it went away. The plants seemed to clean the air, and the idea spread to every garden centre.
In 2019 two engineers at Drexel University, Bryan Cummings and Michael Waring, looked again. They read a dozen studies from 30 years of research and worked out how much air a real plant can clean in a real room.
What they found
The answer was very little. To clean the air as well as the normal air change in a building, you would need between 10 and 1,000 plants on every square metre of floor.
You would need 10 to 1,000 plants per square metre to match normal fresh air.
The old tests were not wrong. They were just done in small closed boxes for many hours. A home is not a closed box. Air comes in and goes out all the time, and that does far more than the plants.
Why fresh air matters
The US Environmental Protection Agency says that some chemicals are on average 2 to 5 times higher indoors than outdoors. They come from cleaning products, air fresheners, paint, glue, new furniture and more.
The simplest way to lower them is fresh air. Astma-Allergi Danmark advises to air out three times a day: in the morning, in the afternoon and before bed. Open the windows wide for 5 to 10 minutes, so the air can pass through. Do it also when you cook, shower or wash floors.
What we do
- We air out three times a day, also in winter. Cold air is dry, so it works fast.
- We open a window when we clean or paint, as the EPA advises.
- We use fewer sprays and air fresheners. Less in, less to air out.
- We keep the plants, because they are nice to look at. That is reason enough.
