Ferns are common houseplants, admired for their lush, feathery fronds. Varieties like the Boston Fern and the Kimberly Queen Fern are fixtures in homes and offices worldwide. Beyond their aesthetic appeal, a widespread belief exists that these plants actively clean the air by filtering out harmful airborne chemicals that accumulate in modern buildings. Investigating this claim requires examining the plant’s biological processes, the origin of the purification theory, and the measured effectiveness in a typical home setting.
The Mechanism of Plant Air Filtration
The ability of plants to clean the air, a process known as phytoremediation, involves two distinct biological systems working together. The first mechanism centers on the leaves, where gaseous pollutants are absorbed through tiny pores called stomata. Once absorbed, the plant metabolizes these compounds, converting them into less harmful substances used for growth or sequestered within the plant tissue.
The second, and often more significant, mechanism occurs within the soil and root system, known as the rhizosphere. The soil surrounding the roots is home to billions of symbiotic microorganisms, including bacteria and fungi. These microbes break down air pollutants that diffuse into the potting soil.
Volatile organic compounds (VOCs), which are common household pollutants, are the primary targets of this biofiltration. Chemicals like formaldehyde, which off-gasses from furniture and building materials, and benzene, found in plastics and synthetic fibers, are absorbed and processed. Air circulation that draws airborne compounds down through the root zone maximizes the exposure to these active microorganisms.
Context: The Initial Studies on Indoor Air Quality
The modern understanding of plant-based air purification traces its roots back to the 1989 NASA Clean Air Study. This research was designed to explore methods for maintaining breathable air in sealed environments, such as future space habitats. Researchers placed common houseplants inside tightly sealed plexiglass chambers to test their ability to remove airborne toxins.
The methodology involved introducing high concentrations of volatile organic compounds, like formaldehyde and trichloroethylene, into these small, controlled chambers. The results showed that certain plants could dramatically reduce the concentration of these chemicals, sometimes removing up to 90% of the pollutants within a 24-hour period. This finding generated significant excitement and was the foundation for the public perception that houseplants are effective air purifiers.
The study successfully demonstrated the physiological capacity of plants to process these toxins under laboratory conditions. However, the findings were based on a non-ventilated environment with pollutant levels much higher than those typically found in a home. The results were intended to show the potential for phytoremediation, not to provide a metric for practical indoor air improvement.
Real-World Effectiveness and Specific Fern Varieties
Subsequent research has clarified the limited practical impact of ferns in a typical home environment. Modern homes have a natural rate of air exchange, where indoor air is constantly replaced with outdoor air, dispersing volatile organic compounds. This air exchange rate is often so high that the filtering capacity of a few potted plants is negligible by comparison.
To measure air quality impact, researchers use the Clean Air Delivery Rate (CADR), which quantifies the volume of air cleaned per unit of time. CADR studies show that a single plant’s cleaning rate is extremely low compared to a standard mechanical air filter. Achieving a measurable reduction in pollutants in a moderately sized room would require an impractical density of plants, often necessitating hundreds per square meter of floor space.
Despite these limitations, ferns remain some of the most frequently cited species for their air-cleaning ability. This includes the Boston Fern (Nephrolepis exaltata) and the Kimberly Queen Fern (Nephrolepis obliterata). The Boston Fern, in particular, was noted in some experiments for having a comparatively high rate of formaldehyde removal.
To maximize the limited purifying effect, placement and care are important considerations. Since the soil microbes are a primary mechanism for detoxification, ensuring the plant is healthy and the soil is active is beneficial. Placing ferns in areas where they can receive sufficient indirect light and high humidity supports their overall health and biological functions. Although ferns alone will not replace a mechanical air purification system, they contribute to a healthier indoor environment and offer aesthetic and psychological benefits.