Do Houseplants Really Purify the Air? A Closer Look at the Science

You’ve probably heard that bringing plants into your home can help clean the air. It’s an appealing idea, suggesting that a few green friends can make your space healthier. We’ll explore the science behind this claim, looking at where the idea came from and what it means for your home today.

The Famous NASA Study and What It Really Found

The popular belief that houseplants are natural air purifiers largely stems from a landmark study conducted by NASA in 1989. The goal was to find ways to clean the air in sealed space stations. Researchers placed various common houseplants in small, sealed chambers and injected specific volatile organic compounds (VOCs) to see if the plants could remove them.

The results were impressive. The study found that certain plants were very effective at removing chemicals like benzene, trichloroethylene, and formaldehyde from the sealed chambers. For example, the Peace Lily was great at removing all three, while the Snake Plant was a powerhouse against formaldehyde. This research was groundbreaking and introduced the concept of using plants as a natural filtration system.

However, it is crucial to understand the context of this experiment. These tests were conducted in small, airtight containers with no air circulation, which is very different from a typical room in a house or apartment. Our homes have much larger volumes of air, plus ventilation from windows, doors, and HVAC systems, which constantly changes the environment.

How Do Plants Clean the Air?

The process by which plants absorb pollutants is called phytoremediation. It works in a couple of ways:

Absorbing Gases: Plants take in gases from the air through tiny pores on their leaves called stomata. This is the same way they absorb carbon dioxide for photosynthesis. In this process, they can also absorb other gaseous pollutants.
Soil Microorganisms: It’s not just the plant itself doing the work. The soil and root system are home to millions of microorganisms. These tiny microbes are incredibly effective at breaking down harmful organic chemicals in the air that get pulled down into the soil. Some studies suggest that the soil microorganisms might be responsible for a significant portion of the air-cleaning effect.

Common indoor air pollutants that plants have been shown to remove in lab settings include:

Formaldehyde: Found in particleboard, furniture, carpeting, and household cleaning products.
Benzene: A common solvent found in paints, plastics, rubber, and detergents.
Trichloroethylene: Used in adhesives, spot removers, and paints.
Xylene: Found in printing, rubber, and leather industries, as well as in vehicle exhaust.
Ammonia: Found in many window cleaners, fertilizers, and floor waxes.

Top Plants from the NASA Study

While the real-world impact might be debated, some plants consistently performed well in laboratory tests. They are also popular, hardy, and beautiful additions to any home.

1. Snake Plant (Sansevieria trifasciata)

Also known as mother-in-law’s tongue, this plant is famous for being almost impossible to kill. It is excellent for beginners. In lab tests, it was particularly effective at filtering formaldehyde, a common household chemical. It is also unique because it converts carbon dioxide into oxygen at night, making it a great choice for bedrooms.

2. Spider Plant (Chlorophytum comosum)

The Spider Plant is another incredibly resilient and easy-to-grow plant. It’s known for its long, arching leaves and the little “spiderettes” it produces, which can be easily repotted. It was noted in the NASA study for its ability to remove formaldehyde and xylene from the air.

3. Peace Lily (Spathiphyllum ‘Mauna Loa’)

With its beautiful white spathes, the Peace Lily is a popular choice for adding a touch of elegance to a room. It topped NASA’s list for its ability to remove all three of the most common VOCs: formaldehyde, benzene, and trichloroethylene. It also has a high transpiration rate, which helps to humidify the air.

4. English Ivy (Hedera helix)

A classic, climbing vine, English Ivy is great for hanging baskets or as a trailing accent on a shelf. It is particularly effective at filtering airborne fecal matter particles, making it a surprisingly good choice for a well-lit bathroom. It also showed a strong ability to remove benzene and formaldehyde in lab settings.

5. Boston Fern (Nephrolepis exaltata ‘Bostoniensis’)

This lush, feathery fern is a natural humidifier. It is considered one of the most effective plants for removing formaldehyde from the air. However, it requires a bit more care than other plants on this list, needing consistent moisture and higher humidity to thrive.

The Reality Check: Plants vs. Ventilation

So, can a few spider plants truly purify your home’s air? More recent studies have put the NASA findings into a real-world context. The conclusion is that while plants do remove pollutants, the effect in a normal home is quite small.

Researchers from Drexel University calculated that to have a meaningful impact on indoor air quality, you would need an enormous number of plants. Their estimates suggest you would need anywhere from 10 to 1,000 plants per square meter of floor space to match the air-cleaning power of a standard ventilation system or a good air purifier. In other words, you would need to live in a dense jungle.

The most effective ways to improve your indoor air quality remain the simplest:

Open your windows: Allowing fresh air to circulate is the fastest way to clear out indoor pollutants.
Use an air purifier: A mechanical air purifier with a HEPA filter is specifically designed to remove airborne particles and VOCs efficiently.
Use exhaust fans: Run the fans in your kitchen and bathroom to remove pollutants at their source.

The Real, Proven Benefits of Indoor Plants

Even if they are not miracle air purifiers, indoor plants offer numerous other scientifically-backed benefits that make them well worth keeping.

Stress Reduction: Studies have shown that simply being around plants can lower blood pressure, reduce feelings of anxiety, and improve your mood. Tending to plants can be a meditative and calming activity.
Improved Focus: Having plants in a workspace has been linked to increased concentration and productivity. The natural green color is easy on the eyes and can help reduce mental fatigue.
Aesthetic Beauty: Plants are a simple and beautiful way to decorate your living space. They add color, texture, and life to any room, making it feel more welcoming and vibrant.

Ultimately, you should absolutely fill your home with plants because they bring joy, beauty, and a connection to nature. While their air-purifying effects may be modest in a real-world setting, their positive impact on your mental well-being is significant.

Frequently Asked Questions

How many plants do I need to actually clean the air in a room? To achieve a level of air purification comparable to an air purifier or opening a window, you would need a very large and impractical number of plants, likely hundreds in a single room. It is best to think of plants as a supplement, not a primary solution for air quality.

Are some plants better than others for air purification? In controlled lab studies, plants like the Peace Lily and Boston Fern showed a higher rate of pollutant removal than others. However, in a normal home environment with air circulation, the difference between plant species is likely negligible. The best approach is to choose plants that you find beautiful and that will thrive in your home’s conditions.

Is it true that plants release carbon dioxide at night? Is that dangerous? Yes, like humans, plants respire and release a small amount of carbon dioxide at night. However, the amount is extremely small and poses absolutely no danger to your health. The oxygen they produce during the day far outweighs the tiny amount of CO2 they release at night.