- A new study reviewed 26 indoor greening systems, including potted plants, living walls, and hydroponic towers, to assess indoor environmental quality.
- It found that larger or engineered systems may improve perceived thermal comfort and, in some cases, reduce fine particulate matter and volatile organic compounds under specific conditions.
- The authors said the air-cleaning effect of a small number of passive potted plants is limited at the room scale in ventilated spaces.
Indoor plants and larger greening systems may improve how indoor spaces feel, but they are not a substitute for ventilation or filtration, according to a new study published in Building and Environment. The paper reviewed evidence on 26 indoor greening systems and assessed how they affect indoor environmental quality across technical, microbiological, health and socio-economic dimensions.
The study was led by researchers at the University of Surrey’s Global Centre for Clean Air Research under the GREENIN Micro Network Plus project. It introduced a ten-question framework to assess indoor greening systems and noted that much of the earlier research relied on short-term or sealed-chamber experiments that do not reflect real buildings.
The review brought together 35 experts from the U.K., Europe, the U.S., Australia, India and Brazil. Indian researchers were part of the collaboration, making the findings particularly relevant for India, where heat stress, air pollution and building conditions shape indoor environmental quality.
Prashant Kumar, lead author of the study, said the team designed the framework to address “a translation gap in the field.” He said earlier research often showed “what plants might do under simplified conditions, but not how they perform in real buildings once ventilation, occupancy, intermittent pollution sources and maintenance are considered.”
Kumar said the framework was intended to move the discussion from “can plants remove pollutants under idealised conditions?” to “under which combinations of ventilation, source strength, and operational control does a given iGI (indoor green infrastructure) system yield a meaningful net change, and at what risk/cost?”
Comfort gains, but not direct cooling
One of the study’s main findings is that some indoor greening systems can improve perceived thermal comfort by up to about 2 degrees Celsius, even when measured room temperature does not fall by the same amount.
Kumar cautioned against reading this as direct cooling of a room. “A perceived thermal-comfort improvement of up to ~2°C without a matching reduction in measured room air temperature is plausible because thermal sensation is not controlled by air temperature alone,” he said. “In other words, the observed ‘2°C’ can reflect a combined microclimate + psychophysiological effect rather than a simple cooling of the room air.”
The paper says the direction of improved comfort appears fairly common, but the size of the effect varies by context and is often stronger in perceived metrics than in instrumental ones.
Limited air-cleaning from passive plants
The study also examined whether indoor greening can reduce pollutants such as fine particulate matter and volatile organic compounds. Here, the findings were more limited than the common claim that houseplants can clean indoor air on their own.
Kumar said meaningful reductions are more likely when indoor greening is treated as “a designed air-treatment system rather than a decorative addition.” He added that this usually means engineered configurations such as “forced-flow botanical biofiltration” or “active green walls,” where airflow is deliberately brought into contact with plant surfaces or an active substrate.
By contrast, Kumar said, “a small number of passive potted plants in a ventilated space often cannot compete with ventilation-driven dilution and the intermittent nature of indoor sources, so any effect can be local, transient, or difficult to detect at the room scale.” He also said that “plant density” alone is not enough to judge performance. “What matters is the treated air fraction,” he said, meaning how much room air actually passes through the active removal zone.
Why context matters in India
The study includes Indian researchers and discusses how these findings may apply differently across climates and building types. Kumar said the findings are “broadly transferable in terms of principles, but not necessarily in terms of effect size.”
He said that in hot-humid regions, “additional evapotranspiration can raise latent loads and dampness risk unless ventilation/dehumidification is managed,” while in hot-dry regions, “moisture addition can be beneficial for comfort.” He also said any real-world application in India would need to consider “dominant indoor sources (especially cooking emissions and resuspended dust), ventilation practices, maintenance feasibility, water availability, power reliability for active systems, and baseline health vulnerabilities.”
Indian research highlights the ‘micro-climate’ effect
Sumit Kumar Mishra, a Senior Principal Scientist at the CSIR National Physical Laboratory (CSIR NPL) in New Delhi, was not involved in the Surrey study but has conducted extensive research on how plants function in real world Indian office settings. Mishra notes that while the technical air cleaning capacity of a single plant might be low, the cumulative micro climatic impact in an urban setting like Delhi is noteworthy.
“In plants, because of evapotranspiration, humidity increases and that humidity—since every particle is not dry—they have affinity to take the moisture,” Mishra says. “They take the moisture and become a bit heavy. And when the weight increases, they are settling gravitationally.”
Mishra’s research suggests that indoor plants can also influence the way outdoor pollution enters a building. “These plants generate such a micro climatic system inside that if pollution has to come from outside, it slows down its speed,” he notes, referring to the rate of pollutant infiltration. Mishra also highlights the psychological and cultural dimensions of indoor greening in India, citing the traditional use of Tulsi and the mood boosting potential of volatile organic compounds released by plants.
“Using plants could be helpful as a sustainable measure in typical urban settings like Delhi and NCR,” Mishra says. However, he acknowledges potential limitations, noting that some individuals may have sensitivities or allergies to the microorganisms found in potting soil.
What it means for homes and small offices
For households and small offices, Kumar said the current evidence supports a narrower role for indoor plants. “The most defensible message from the current evidence is that indoor plants are a credible wellbeing and comfort co-intervention, but they are not a substitute for ventilation, filtration, or source control,” he said.
He added that the paper supports benefits in “perceived pleasantness, stress reduction, and sometimes thermal acceptability,” but “cautions against overstating air-cleaning from a small number of potted plants at room scale.” Kumar also said that plants “do not meaningfully solve CO₂ buildup compared with adequate ventilation.”
“For any serious IAQ aim, prioritise kitchen extraction, low-emission products, and appropriately designed ventilation/filtration,” he said.
More evidence still needed
The study called for more long-term work in occupied buildings. Kumar said the next step should include “multi-season field trials in real buildings” that measure “ventilation/air exchange, occupancy patterns, and indoor source events alongside iGI interventions.”
He said stronger real-world evidence will be needed before policymakers can rely on these systems for building guidance. For now, the study places indoor plants in a limited role: they may support comfort and wellbeing, while meaningful pollutant reduction is more likely in engineered systems that are properly designed and maintained.
Banner image: While indoor green infrastructure can improve indoor settings, it is not a replacement for ventilation. Researchers say that earlier research often showed what plants might do under simplified conditions, but not how they perform in real buildings. Representative image by Simone D. McCourtie / World Bank via Flickr (CC BY-NC-ND 2.0).
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