Purifying the air with plants

Do Plants Purify Air?

Indoor plants
Photo: Huy Phan.

Do a web search on air purification by plants and you’ll find hundreds of articles on the subject. There are some unreliable sources such as home decor magazines and trendy blogs, but also more serious media (such as the Laidback Gardener blog!) that have written about the subject. They often give lists of the best air filtering plants. I got caught up in this myself. I never really asked myself whether or not plants purify the air because it just seemed so obviously true! Today, I must unfortunately announce to you that it is not actually the case, at least not as much as we thought.

Indoor plants in NASA's biohome
Photo: Bill Wolverton.

Ground Control to NASA? What Seems to Be the Problem?

It all started with a NASA study published in 1989, in collaboration with Associated Landscape Contractors of America: Interior Landscape Plants for Indoor Air Pollution Abatement. These compounds are released from many products and materials found in our homes, such as paint and certain cosmetics. NASA astronauts, working in a restricted environment, could be exposed to these VOCs, hence this study.

What the study shows is that some plants have the ability to clean the air of VOCs. After the study was released, the media spread the good news: plants filter air! So what’s the problem, man?

Indoor plant in a plexiglass cube for a purification test
Study on the ability of plants to filter air, done in plexiglass cubes. Photo: Bill Wolverton.


To start with, the study was conducted with plants placed in Plexiglas cubes of approximately 15 and 30 cubic feet (0.4 and 0.8 m3). A small room of 8’x8’x8′ (2.5m x 2.5m x 2.5m) has a volume of 512 cubic feet (15.625m3). With these figures, one would need between 17 and 34 houseplants to purify the air. But an apartment or a house is not a Plexiglas cube and therefore these figures don’t even apply. To date, I’m not aware of any study that looks at the filtering effect of plants in the context of a normal residence. (I see some of you are still thinking about how to get 40 plants into your bedroom.)

Another part of the study showed that roots and soil microorganisms were the most effective in filtering VOCs. The air was forced through activated charcoal in which plants were growing. Again, this has nothing to do with the homes you and I live in! And, let’s not forget that only a few pollutants were tested in the NASA study. What about the others?

Diagram of an air purifier that includes indoor plants
Activated charcoal filter model in which plants grow. The air is forced through the charcoal and the root-bound micro-organisms do the work. Photo: Mark Nelson.

How Does It Work?

Now I’m aware that my houseplants won’t replace an air purification system, but I’m still curious as to how plants transform these compounds. Well, they can absorb VOCs through their leaves and transport them to their roots where microorganisms break them down and convert them into sugars, oxygen and even plant matter!

Real Benefits of Houseplants

But don’t get rid of all your houseplants just yet! They still have well-documented benefits for humans. For example, working with plants reduces stress levels and can relieve people suffering from depression and anxiety. Their mere presence in our environment can improve our attention span. In addition, one study showed that the presence of plants could help us heal faster after surgery. Other studies have found that plants increase productivity and creativity in the workplace.

Sansevieria or mother-in-law's tongue (Dracaena trifasciata)
The snake plant or mother-in-law’s tongue (Dracaena trifasciata) is said to be indestructible. Photo: Larry Hodgson.

Which Plants to Choose?

Although NASA has compiled a list of plants that effectively purify the air, all plants have this ability. The best plants for our health are those that are healthy themselves. Choose plants that will grow well in your home. Here’s a list of plants that can’t be killed if you’re not sure you have a green thumb.

So what do we do with all this pollution? Purifiers or air exchangers do their job well, but the easiest way is to open a window from time to time!

4 comments on “Do Plants Purify Air?

  1. The release of oxygen was all I need to know.

  2. Sad but true. However, the boost to my mental health having a house full of plants is so still the best benefit.

  3. I had bought into the hype too, but not my husband. He knew better I suppose! Great article!

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