Do Houseplants Actually Improve Air Quality?
Have you heard that houseplants improve air quality? Is this real, or just another houseplant myth? In this article, gardening expert and houseplant enthusiast Madison Moulton looks at if there's actually science to back up these claims, or if it's just another gardening myth.
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When new indoor gardeners are looking for a new plant to add to their collection, one of the most common questions I get asked (after which houseplant grows best in low light) is, which plants can purify the air in my home?
There has been some confusion around this topic in recent years. One quick internet search will return side-by-side results naming it both true and a complete myth. Some claim the results are undeniable, while others believe there is no truth to it at all.
So, I put my science cap on to find out what the current research tells us – not only in these controlled experiments but in our own homes.
The Short Answer
The widespread belief that houseplants improve air quality is typically traced back to the NASA Clean Air Study of 1989. This studyh showed that several houseplants can remove harmful compounds from the air in closed environments.
However, later studies have explained that the effectiveness of plants in cleaning the air in our homes is much lower due to size and airflow from simple things like open windows.
Although plants don’t purify the air in our homes as well as they do in controlled environments, there are still many reasons to grow them.
The Long Answer
Unfortunately, like most things, there isn’t really a definitive answer to the question. To trace the various studies on houseplants and air quality, we have to return to where it all started: the 1980s.
Where Did the Idea That Houseplants Improve Air Quality Start?
Although the suggestion that houseplants can purify the air likely didn’t start with NASA, they certainly popularized it.
In 1989, researchers at NASA conducted a study to assess ways to clean and purify the air in sealed environments. In the introduction, the paper explains the rise of indoor air pollutants in the 1970s. This led to a phenomenon called ‘sick building syndrome.’
In sick building syndrome, people reported allergy-like symptoms, such as itchy eyes, respiratory congestion, drowsiness, or headaches. The main pollutants referenced are construction materials used in the building’s construction or materials in the building and people themselves – especially when large crowds are packed into tight spaces.
NASA had identified issues with indoor air pollution in sealed environments in space several years before this study. According to the paper, researchers had been working on ways to solve the problem for years. Thus, the Clean Air Study was born.
Well, its official title is actually “Interior Landscape Plants For Indoor Air Pollution Abatement,” but ‘Clean Air’ is far more catchy!
To conduct the study, the team placed a number of common houseplants into sealed chambers. The chambers had a height of 60 inches and a width of 30 inches. These chambers were filled with Volatile Organic Compounds (VOCs) at certain intervals. The air was tested 24 hours later to uncover these results:
“Low-light-requiring houseplants, along with activated carbon plant filters, have demonstrated the potential for improving indoor air quality by removing trace organic pollutants from the air in energy-efficient buildings. This plant system is one of the most promising means of alleviating the sick building syndrome associated with many new, energy-efficient buildings.”
“The plant root-soil zone appears to be the most effective area for removing volatile organic chemicals. Therefore, maximizing air exposure to the plant root-soil area should be considered when placing plants in buildings for best air filtration.”
The NASA Clean Air Study in Practice
The results of the study slowly spread. It created the belief that keeping a few of the listed houseplants indoors can improve air quality. As interest in houseplants spiked rapidly in the mid-2010s, searches for ‘air purifying plants’ grew. They reached their peak in July 2020.
But, as often happens with scientific studies, the results are usually simplified and taken out of context. In practice and out of heavily controlled environments, the effects of houseplants on purifying the air aren’t as dramatic as they may seem.
Several studies have been conducted since the NASA study. These studies assessed the levels of VOCs in homes and offices, the effects on human health, and ways to combat the problem. A review of these studies conducted in 2014 explained that the effects of indoor plants in real-life environments are largely inconclusive:
“Studies conducted in indoor environments show mixed results and VOC emission rates, ventilation rate and VOC emission by the plants themselves were potential influencing factors. A universal answer to the question: “Can ornamental potted plants remove VOCs from indoor air?” cannot be given yet.”
“While the plant’s ability to take up VOCs is well documented in laboratory studies, the effect of plants on indoor air in complex environments like offices requires further investigations to clarify the full capacity of plants in real-life settings. It is evident from this review that future research is needed to fully understand indoor VOC removal by plants.”
Another review conducted in 2020 was far more pessimistic. It explained that 10-1000 plants would be required per square meter of office space to reach the same level of VOC removal “that outdoor-to-indoor air exchange already provides in typical buildings.”
All this science boils down to this. We do have evidence that indoor plants can purify the air. But only in very closed and controlled environments. We can’t extrapolate these results to our homes and offices where airflow is much higher.
In other words, if you want to clean your air indoors, you’re probably better off just opening a window. This depends on where you live, of course.
New Studies Into Houseplants and Air Quality
As there is no real scientific consensus on the effectiveness of indoor plants in cleaning the air indoors, studies are still being conducted.
One recently published study looked at the ability of three common indoor plants to remove nitrogen dioxide (NO2). It found that the plants did remove the pollutant but at varying degrees. The size of the environment has a big impact on results, as well as the existing airflow in the environment.
What do these results mean for indoor gardeners? For starters, the more plants you purchase, the better chances you have of improving the air quality in your home. It may not be possible to reach 1000 plants per square meter of space. But avid houseplant growers can certainly try!
Secondly, just because their effectiveness is limited, it doesn’t mean you shouldn’t keep plants indoors anyway. They may positively influence indoor air quality – just don’t expect them to solve all your problems.
And finally, there are so many other reasons to grow houseplants apart from their air-purifying abilities.
Plants are proven to improve mental health and well-being. Especially for those who tend to spend a lot of time indoors and away from nature. They also have the potential to boost productivity and generally improve the overall look of your home.
Plus, caring for houseplants and watching them grow provides a sense of accomplishment unlike any other – one of the things that got me hooked in the first place.
Final Thoughts
The results may not be as definitive as some make them seem. However, houseplants do have the potential to improve indoor air quality. It just depends on the environment and amount of plants you have. Despite the limited impact, there are many other reasons to keep houseplants indoors. This means expanding your collection will be well worth the effort.
