Can Indoor Plants Really Increase Your Air Quality?

Before getting into the weeds on this topic, let me state that this is a perfect example of how legitimate and well funded scientific study data gets warped and twisted to the point where nurseries, plant shops, social media sites, blogs, and "influencers" start believing their own bullshit, and use it to take advantage of consumers so they will buy more plants.

These "experts" have been pimping the air purifying benefits of houseplants for years, long touting them as "natural air purifiers", based on the widely cited NASA study conducted by B.C. Wolverton in 1989, titled Interior Landscape Plants for Indoor Air Pollution Abatement. The study suggested that certain indoor plants could absorb harmful volatile organic compounds (VOCs) like benzene, formaldehyde, and trichloroethylene from the air, making them seemingly ideal for improving indoor air quality. However, as appealing as this idea is, it’s essential to critically examine whether indoor plants can truly deliver on this promise, especially in a typical home environment.

The NASA Study - Where the seed of a lie was born.

The NASA study led by B.C. Wolverton, Interior Landscape Plants for Indoor Air Pollution Abatement, was a pioneering effort to explore the potential of indoor plants to improve air quality. Conducted in 1989, the study was initially designed to find solutions for maintaining air quality in sealed environments, such as space stations, where traditional ventilation methods would be impractical. While the results were promising within the scope of the experiment, the study’s findings have often been misinterpreted or overstated when applied to typical home environments.

How the NASA Study Was Conducted

Wolverton’s research was performed in a series of small, sealed chambers designed to replicate the confined conditions of a spacecraft. Each chamber was outfitted with a specific plant species, along with a consistent source of VOCs, such as benzene, formaldehyde, or trichloroethylene. The air inside these chambers was monitored over time to measure the plants’ ability to remove or reduce the concentration of these pollutants.

The experimental setup included:

Sealed Chambers

The plants were placed in tightly controlled, small chambers where the air exchange was minimal, allowing for a precise measurement of the change in VOC levels. These chambers were completely sealed, ensuring that any reduction in pollutants could be attributed directly to the plants and the associated soil microorganisms.

High Concentrations of VOCs

The levels of VOCs introduced into the chambers were significantly higher than what is typically found in most homes. This high concentration provided a strong incentive for the plants to absorb these compounds as part of their natural respiration and photosynthesis processes.

Short Duration

The experiments were conducted over relatively short periods, allowing researchers to observe the immediate effects of the plants on air quality. However, these short-term studies do not necessarily reflect the long-term dynamics of air quality in a more complex, real-world environment.

Controlled Variables

Factors such as temperature, humidity, and light levels were strictly controlled to optimize the plants’ ability to metabolize VOCs. In a typical home, these factors can fluctuate significantly, impacting the efficiency of plants in removing pollutants.

Why the NASA Study’s Results Are Not Directly Applicable to Homes

While the NASA study demonstrated that plants could absorb VOCs under controlled conditions, several factors limit the applicability of these findings to everyday home environments:

Chamber Size vs. Room Size: The small, sealed chambers used in the NASA study are vastly different from the open and variable spaces in homes. In a typical room, air circulation is much greater, and the air volume is significantly larger. This means that any VOCs present are more diluted, and the impact of a single plant is proportionally reduced. The small chamber size in the study allowed the plants to have a much more concentrated effect on air quality than would be possible in a typical home.

Air Exchange Rates: Homes are not sealed environments. Even in well-insulated houses, air is constantly exchanged with the outdoors through HVAC systems, windows, doors, and natural leaks. This constant air exchange dilutes both the VOCs and the potential impact of plants. In the NASA study, the lack of air exchange meant that any reduction in VOCs could be attributed directly to the plants, but in a typical home, the air exchange would make it nearly impossible for plants to make a significant difference.

Number of Plants Required: To replicate the air-purifying effects observed in the NASA study in a typical home, an impractically large number of plants would be needed. Research has shown that you would need between 100 and 1,000 plants per square meter to achieve a similar level of VOC reduction as was seen in the sealed chambers. Most unlikely gardeners would find it difficult, if not impossible, to accommodate such a dense concentration of plants in their living spaces.

Variable Pollutant Sources: The NASA study introduced specific pollutants in controlled amounts, but in a home, the sources and levels of VOCs can vary widely depending on household activities, furniture, cleaning products, and even outdoor pollution. This variability further complicates the ability of plants to consistently reduce indoor pollutants, as they may not be able to keep up with fluctuating levels of VOCs introduced by daily activities.

Impact of Soil Microorganisms: Another critical factor in the NASA study was the role of soil microorganisms in breaking down VOCs. While these microorganisms can indeed contribute to air purification, their effectiveness depends on the health and maintenance of the soil. In a typical indoor plant scenario, improper watering, over-fertilization, or the use of inert soilless grow mixes could disrupt the microbial balance, reducing the media’s ability to contribute to VOC reduction.

Lack of Long-Term Data: The NASA study was conducted over relatively short periods, focusing on immediate effects rather than long-term sustainability. In real-world settings, the long-term impact of plants on indoor air quality is less clear, especially as the plants and soil age, dust accumulates, and potential pests or diseases are introduced.

The Practicality of Using Plants as Air Purifiers

In your house and living areas, the effectiveness of plants purifying the air is pretty much useless. Studies conducted after Wolverton’s have shown that the number of plants required to achieve a significant level of VOC reduction in a typical home would be impractically large. A 2019 study published in the Journal of Exposure Science & Environmental Epidemiology found that to match the air-cleaning effect of even a modest ventilation system, one would need hundreds, if not thousands, of plants per square meter.

For instance, to remove a significant amount of formaldehyde from the air in an average-sized room, you might need anywhere from 100 to 1,000 plants per square meter, depending on the specific plant and the pollutant involved. This number is far beyond what any homeowner could realistically maintain. Furthermore, the dynamic air circulation in homes—due to HVAC systems, windows, and doors—dilutes the concentration of VOCs, making it even less likely that plants could effectively clean the air.

The Hidden Risks: Plants and Indoor Air Quality

While plants are often associated with enhancing indoor environments, they can also introduce elements that might degrade air quality. Here are some potential risks:

Dust Accumulation: Indoor plants can accumulate dust on their leaves. Over time, this dust can be released back into the air, contributing to particulate matter that can irritate the respiratory system, especially in individuals with allergies or asthma.

Mold Growth: The soil in potted plants is a natural breeding ground for mold, especially if overwatered. Mold spores can become airborne and contribute to indoor air pollution, potentially leading to respiratory issues and exacerbating conditions like asthma and allergies.

Fungal Spores: Similar to mold, certain fungi can thrive in the soil of indoor plants. Some of these fungi produce spores that can be released into the air. While not all fungal spores are harmful, some can cause allergic reactions or respiratory problems.

Pests: Indoor plants can sometimes harbour pests like fungus gnats, which are attracted to moist soil. These tiny insects can become a nuisance and, in some cases, may even affect indoor air quality by carrying bacteria or other pathogens.

Balancing Benefits and Risks

While the risks mentioned above should not deter you from enjoying indoor plants, they do highlight the need for balanced and informed decisions. To minimize the potential negative impacts on indoor air quality:

Regular Cleaning: Dust the leaves of your plants regularly to prevent the accumulation of dust that could re-enter the air.

Proper Watering Practices: Avoid overwatering your plants to reduce the risk of mold and fungal growth. Ensure that the pots have proper drainage and that the soil is not overly saturated.

Ventilation: Ensure that your home is well-ventilated. Good airflow can help to disperse any airborne mold spores, dust, or VOCs that plants might introduce.

Conclusion: A Holistic Approach to Indoor Air Quality

Wolverton’s NASA study laid the groundwork for understanding how plants interact with indoor air pollutants. However, when applied to real-world conditions like and unlikely gardener's home, the practicality of using plants as a useful means of air purification is pretty much a waste of time. While plants can contribute to a healthier indoor environment by improving humidity and providing aesthetic and psychological benefits, they are not a replacement for effective ventilation, air purifiers, and other methods of reducing indoor air pollution.

Moreover, homeowners should be aware that plants can introduce dust, mold, and fungi into the home, potentially decreasing air quality if not properly managed. Therefore, while incorporating plants into your indoor spaces can be beneficial, it should be part of a broader strategy for maintaining a healthy indoor environment.

In the end, indoor plants may not be the air-purifying powerhouses they were once believed to be, but they can still play a valuable role in creating a more pleasant and visually appealing living space—provided you take care to mitigate the potential risks they might introduce.

To quote Mulder from the X-Files, "Question Everything"