The Calathea genus, recognized for its striking, vividly patterned foliage, is a highly sought-after houseplant. Many consumers acquire it under the belief that it significantly purifies the air inside their homes. This reputation stems from the plant’s natural biological processes, often marketed as a comprehensive solution for improving indoor air quality. This article investigates the scientific basis of this claim and the actual effectiveness of Calathea in a typical living environment.
The Origin of the Air Purifier Claim
The widespread notion that houseplants, including the Calathea, can significantly clean indoor air traces its roots back to a 1989 study conducted by the National Aeronautics and Space Administration. This research, known as the NASA Clean Air Study, investigated methods for air revitalization within sealed environments, such as future space stations. Scientists placed individual potted plants inside small, airtight plexiglass chambers, approximately 0.9 cubic meters in volume. In this highly controlled, closed environment, the researchers introduced concentrated amounts of specific airborne toxins. The compounds tested were volatile organic compounds (VOCs) commonly found in household goods, including formaldehyde, benzene, and trichloroethylene. The results demonstrated that, under these extreme laboratory conditions, certain plants were capable of removing a high percentage of these pollutants quickly. This finding established the scientific precedent for the air-purifying reputation surrounding many common houseplants.
How Plant Filtration Works
The mechanism by which any houseplant processes airborne pollutants involves a dual-action system utilizing both the foliage and the soil. The leaves absorb gases through tiny pores on their surface, known as stomata. During this gas exchange, the plant takes in carbon dioxide for photosynthesis, but it also inadvertently absorbs airborne VOCs. However, the primary site for the removal and breakdown of these pollutants is the root-soil system. Air circulates around the pot and is drawn into the soil, where a complex ecosystem of microorganisms resides. These soil microbes, which form the rhizosphere, metabolize the VOCs. They effectively break them down into less harmful substances that the plant can use as nutrients. This symbiotic relationship is responsible for the majority of the air-cleaning effect observed in the original laboratory experiments.
Practical Effectiveness in Home Environments
The positive results from the NASA study, while scientifically accurate within their context, do not translate directly to the dynamic environment of a typical home. The most significant difference between the laboratory chamber and a residential room is the air exchange rate (AER). A home is not sealed; air constantly moves in and out through windows, doors, and ventilation systems, a process that continually dilutes indoor pollutants. In a standard ventilated building, this natural air exchange removes volatile organic compounds much faster than a small number of houseplants can absorb them.
To achieve the same air cleaning rate as a building’s ventilation system, current research indicates an impractical density of plants would be necessary. Studies suggest that between 10 and 1,000 potted plants would be required for every square meter of floor space to make a meaningful difference in overall air quality. While a Calathea technically possesses the biological capacity to filter air, its practical impact on the air quality in an average-sized room is statistically insignificant. The presence of a few plants provides negligible benefit compared to opening a window or using a mechanical air filter. The primary value of the Calathea in the home is its aesthetic contribution and the psychological benefits of being surrounded by nature.