Testing If House Plants Clean Air – Here’s How Many You Need

I recently built an air quality sensor to test the air in my home and I found that it was much worse than the air outside. There is a growing body of research that shows similar trends for homes across the planet. All of this made me wonder, can we really use plants to clean the air in our homes? So, I spent a couple of weeks running an experiment where I collected over 10,000 data points to see if plants really can clean the air in my home. 

Testing If Houseplants Can Clean Air Experiment

The experiment was pretty straightforward. I built a clear box and put a plant in the box with an air quality sensor and sealed it off. To seal it off I used bubble wrap, because when the weight of the boxes presses down on the bubble wrap, the bubbles form a perfect seal by wrapping around the box. Next, I put another air quality sensor in a separate box and sealed it off as well so I had something to compare the plant box to. Last, I started the sensors and programmed them to collect air samples every five minutes for five days. If the air quality in the plant box improves more than the air quality without the plant, we can say that plants do in fact clean air. In this experiment I also tried putting multiple plants in one box and using a grow light and i’ll explain why in a moment. I also visited a plant nursery to see what the air quality was like in a place that had hundreds of plants in it for many years and i’ll get to that in a moment as well. If you want to build an air quality sensor like this one yourself check out this tutorial

Before we get to the results, here’s a quick note on the importance of air quality. Poor air quality in the home is caused by molecules such as benzene, formaldehyde, and many others. These molecules are found in everything from furniture to paint, so you probably have many of them in your home right now. These molecules are capable of causing many different human health issues, so if we’re going to depend on plants to clean air in our homes we need to be sure they can actually clean air.

Can Houseplants Really Clean Air?

Let’s go to the results. In the first experiment with just one plant, the air quality in the plant box got worse, but the air quality in the empty box got even worse than the plant box. Air quality is measured in ppm or parts per million which is basically a measurement of the number of particles of something in the air for every 1 million particle sampled. For example, if there are 20 ppm of carbon dioxide in the air it means for every 1 million air particles 20 of them are carbon dioxide. Going back to the experiment, the air quality in the empty box got worse by 42 ppm while the air quality in the plant box got worse by about 22 ppm. This means less particles of pollutants were detected in the plant box after 5 days, even though they started at about the same point. 22 ppm really isn’t that much so I decided to take it a step further and put a second plant in the box and run the experiment again to see if the air quality would continue to improve. This time the air quality in the empty box got worse by about 20 ppm but the air quality in the plant box improved by about 20 ppm. This is interesting because the first experiment with one plant improved the air quality by about 20 ppm and the second experiment with two plants improved the air quality by about 40 ppm. It’s as if each plant was improving the air quality by about 20 ppm. 

But it doesn’t stop here. One of the last things I tried was increasing the amount of light. The room I ran the experiment in only has one little window on one side of the room, so once it got dark, I put a grow light on the plant box for about 10 hours for each of the five days to add to the sunlight the plant was already getting. One of the reasons why this is important is that plants remove particles from the air through photosynthesis, so more light should mean more photosynthesis, which should mean more pulling pollutants out of the air. Not only that, but grow lights use blue and red light because they help plants grow the fastest. This is why indoor agricultural farms use blue and red light. When I put two plants in the plant box with the grow light something really interesting happened. The air quality in the plant box improved for the entire first day and probably would have continued to improve but the box started to fill with humidity, which may have been caused by the grow light. While it’s hard to say exactly how much the air quality would have improved it seems it would have improved by another 20 parts per million. 

So what does all this mean for your home? Well, to get a similar result in a bedroom that’s just 10 feet by 10 feet with standard eight foot height, you would need about 533 plants just to improve the air quality by about 20 parts per million which really isn’t that much.

But wait, what about the plant nursery? What was the air quality in the plant nursery and was it better than the air in my home? This nursery has hundreds if not thousands of plants in there year round, so if anywhere is going to see improved air quality from plants it’s going to be this place. The air quality in the plant nursery was over 150 parts per million better than it was in my home, which is way better than the 20 parts per million I estimated plants could do, but still may not be enough to properly clean the air in your home. In other words, if I ran the experiment longer and controlled for humidity it’s possible i’d get similar results. So overall it does seem that plants have some ability to clean air but they probably shouldn’t be the main way of cleaning the air in your home. Instead, you’ll need to focus on other means of filtration, for example from open windows, filters, and air purifiers.

If you’d like to check out some of the other experiments I’ve tried, check out this article next.

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