Garden Myths - Learn the truth about gardening

Kamal Meattle – Plants and Air Purification

In 2014 I wrote a post called A Garden Myth is Born – Plants Don’t Purify Air, which has become one of my most popular posts. A recent comment on that post about a video by Mr. Kamal Meattle has prompted me to write today about another story related to plants purifying air.

Mr. Kamal Meattle has become well known for a short TED Talk video where he talks about converting an office building in New Delhi, into the cleanest building in India. His secret is the use of air purifying plants.

Plants cleaning the air in an office, desk designed by Julio Radesca

Plants cleaning the air in an office, desk designed by Julio Radesca

The Kamal Meattle TED Video

The place to start is with the video which is quoted and discussed in hundreds of places on the internet as proof of the fact that plants purify air. It has been watched by almost 3 million people.

What does the video imply?

  • Plants purify the air by remove formaldehyde and VOCs (volatile organic compounds).
  • Plants produce fresh air.
  • Plants have reduced the incidence of several medical issues by improving the quality of air.
  • Government of India has published a study verifying these facts.

I use the word ‘imply’ here since the video tends to give you a different impression the first time you watch it, than when it is watched and listened to with care.

What does the video actually say?

  • No data is presented to show that plants reduce the level of formaldehyde or VOCs.
  • No data is presented to show that oxygen levels have gone up.
  • 1,200 plants were used in a 50,000 sq ft building that housed 300 occupants.
  • The only study mentioned was done by the India government – no data from it was presented.
  • The term ‘fresh air’ is never defined.

In fairness to Mr. Kamal Meattle this was a mini TED presentation with limited time available, but it is surprising that there is no data presented to support the ideas presented.


If the above video does not run try this link;

Some Back Ground Information About Mr. Kamal Meattle

Mr. Kamal Meattle is the CEO and director of Paharpur Business Center, a company that rents out clean air office space to other companies. Kamal has been active in trying to reduce pollution problems in India and continues to look for new technologies that can be used to solve air quality problems.

Mr. Meattle has received several awards for creating and maintaining a building that meets high air quality standards.

National Geographic reports that “Since January 2013, Meattle’s company has created plant-based air-filtering systems for more than 700 homes in India’s capital. It’s also working to clean the air inside the embassy schools of the United States and Germany”. It is clear that his company is in the business of selling clean air solutions.

Changes Made to the Building

If we return for a moment to the video and try to understand what was done to the building to improve air quality it seems fairly simple. Add 1,200 plants of waist or shoulder height to the building which has 50,000 sq ft. That is a lot of plants, but it is also a big building. It works out to a plant for every 41 sq ft, or one plant per 10′ x 4′ area.

An average home of say 1,500 sq ft would need 37 plants to have an equivalent set up.

The problem with the video is that it does not tell the whole story.

It turns out that many of the plants are located in a greenhouse situated on the roof of the building. The incoming air flows through this greenhouse before entering the building. I think it is reasonable to assume that plants sitting in a sunny greenhouse will have higher metabolism and therefore be much more effective at cleaning air than the same plants sitting in the dark corner of a home. Even a sunny window can’t match the sun provided by a roof top greenhouse.

The real problem however is that the building was also outfitted with a sophisticated air cleaning system for removing chemicals from the air. The incoming air is cleaned by this system before it goes through the greenhouse. The building has both an air cleaning system and plants.

Why was this significant point not mentioned in the video?

The Study by the India Government

I was not able to find the study that looked at the effect on plants on the air quality in the building in question. I checked the Paharpur Business Center website to see what evidence they might have to support their claims – none was found. I then contacted Mr. Meattle and he was very kind in replying promptly. He forwarded a copy of the study to me.

A summary of the report can be found on the PBC web site and the full report can be downloaded from there.

The study does not make any comment about the plants ability to remove pollutants from the air. In fact it does not mention plants. It was never the intent of the study to look at this aspect. Instead the study looked at health issues inside the building and compared them to the general Delhi population.

The study referenced in the video has nothing to do with plants.

Where is the Data?

I had asked Mr. Meattle for information showing that the plants reduced the chemicals in the air. He replied with “There have been many studies done over the years. We are not a research institution and hence these were done for our own interest.” But his company is in the business of selling plant air cleaning systems. One would expect at least some internal data to support their claims.

He did send me a picture of their current air quality, but it shows that both inside the building and outside the building have total VOC levels of 0 ppb. The zero value for Dehli is not correct. I’ll give them the benefit of doubt and assume the VOC’s were not being monitored.

There seems to be no data to show that the plants are removing chemicals from the air.


I want to be very clear about what we know and don’t know.

I have no doubt that the building in question has supplier air. I also believe the Mr. Meattle has done a good job of finding ways to clean the air in his building and that he firmly believes that plants play a big role.

The plants do remove CO2 and add O2 to the air. Although this is good for human health, it is not the question being asked here. This post is all about removing organic chemicals like benzene and formaldehyde.

The building was set up in 2008, the TED video is dated 2009 and it is now 2016. In that time it would have been quite easy to test the level of organics in the building, with and without plants. If done through a university the results could be published in a peer reviewed journal.

One is left wondering why such a simple test was not done?

The National Geographic reported that John Girman, former senior science adviser at the U.S. Environmental Protection Agency’s Indoor Air Division, said “a 1,500-square-foot house would need 680 plants to duplicate NASA-like benefits, and the result would be an indoor jungle” .  Interestingly, in my previous report on the NASA study I figured that a 1,500 sq ft home would need 350 large plants or 750 small plants.

The work by Mr Meattle is interesting and worthwhile, but the currently available data does not support the idea that plants clean the air.


  1. Can Houseplants Really Clean the World’s Smoggiest City?
  2. Photo source, used by permission; Julio Radesca

10 Wasp Myths That Will Surprise You

Wasps are feared and hated. Granted they do sting if you disturb them but that is no reason to fear them. In this post I will look at 10 wasp myths that will surprise you. Armed with this new knowledge I hope that you will learn to either like wasps or at least hate them less.

As a general background review of wasp facts have a look at Understanding Wasps – They Are Not Evil!

Paper wasp nest being built - 10 Wasp Myths That Will Surprise You

Paper wasp nest being built

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Dynamic Accumulators – Are They Beneficial to the Garden?

Dynamic accumulators are plants that accumulate higher than average nutrients in their leaves. Some people grow these plants and then either mulch with them or compost them so that these extra nutrients are made available to other plants. This is particularly popular in permaculture circles, but it is also used a lot in organic gardening.

On the surface this sounds like a great idea. Use plants to fertilize your other plants. How can you get more organic than this.

In this post I will look at the pros and cons of using dynamic accumulators to try and understand how beneficial they are to gardens.  In the process I’ll also uncover some myths about dynamic accumulators.

Dynamic accumulators - Is it worth growing them?

Dynamic accumulators – Is it worth growing them?

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Canada 150 Tulip – Confusion About Cultivar Names

Canada will celebrate its 150th birthday in 2017. To mark this celebration, Canada is launching a special tulip called ‘Canada 150’. The white and red colors of the tulip mimic the colors in our flag.

Where did the Canada 150 tulip originate? There are several stories floating around about its origin but much of this is not true. Canadians have been told that the tulip is only sold through a Canadian hardware stored called Home Hardware and is available in limited quantity. So it should be no surprise that ‘imposter tulips’ have been introduced into the Canadian market place. People will do anything for a loonie (the common name for our $1 coin).

Tulip 'Canada 150' aka Tulip ‘Carnaval de Rio’

Tulip ‘Canada 150’ is the same plant as Tulip ‘Carnaval de Rio’

Follow me as I try to unravel the mysteries of the special Canada 150 tulip and learn more about the confusing world of naming plant cultivars.

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Comfrey – Is it a Dynamic Accumulator?

Comfrey (Symphytum officinale) is probably the most popular dynamic accumulator. Permaculturists swear by it, and organic gardeners use it frequently. Thousands of web sites make all kinds of claims for it and if you believe the claims everyone should be growing comfrey to add nutrients to compost, mulch soil, and make plants grow better.

All of these benefits are derived from the fact that comfrey is one of the best dynamic accumulators – or so people claim. It is time to have a closer look at this miracle worker.

Comfrey dynamic accumulator

Comfrey – Is it a Dynamic Accumulator?

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