It is claimed that some houseplants purify the air of our homes. They are said to rid the indoor environment of pollutants, in turn improving our breathing, our mood, and our overall health. So, is it true, and, if so, how many plants does it take to clean a room?
The origin of the trend for air-purifying plants is a study by NASA that took place in the 1980s. Various plants were shown to clean the air within a sealed chamber that had similar conditions to the inside of a spaceship. After this pioneer research, further studies confirmed the ability of plants (such as weeping fig and peace lily) to improve air quality. The science was then applied to plants in the home, creating a huge demand for houseplants.
However, experts have doubted whether studies carried out in small sealed chambers that offer plants optimum growing conditions can be applied to the average home, which is ventilated and doesn't allow plants to photosynthesize at their peak. In 2020, a review in the Journal of Exposure Science and Environmental Epidemiology concluded that potted plants cannot improve indoor air quality as a result of the ventilation that most buildings possess, unless one had '10 to 1000 plants/m2 of a building's floor space'. This amount of houseplants would equal the ability of indoor-outdoor air flow to remove volatile organic compounds (VOCs) that pollute our homes via a manner of sources (from carpets to nail polish). In other words, using houseplants to purify the air is pointless if you regularly open your windows or have other forms of good ventilation.
This sentiment was echoed in 2021 in a study conducted at the University of Birmingham, which found that houseplants were only effective at reducing the pollutant nitrogen dioxide (NO2) in certain conditions and where there were sufficient plants: 'approximately five plants per small, unventilated office could provide broadly similar health benefits in terms of life saved, as are estimated to result from clean air policies in urban areas,' was the conclusion. The same study also found that indoor 'green walls' of plants were effective at removing CO2, if additional lighting was in place. The university carried out further research in conjunction with the RHS in 2022, which showed that potted peace lily (Spathiphyllum wallisii), corn plant (Dracaena fragrans), and fern arum (Zamioculcas zamiifolia) could reduce NO2 by up to 20 per cent if there were at least five plants 'in confined indoor spaces that are poorly ventilated and/or located in highly polluted areas'. In a larger office or home subjected to pollution (for example, next to a busy road), a greater number of plants would be required. Unlike CO2 reduction, the plants did not require enhanced growing conditions in order to lower NO2.
So, the takeaway is that if your home is unventilated or the outdoor air regularly entering it is polluted, then air-purifying plants are a great benefit, but one or two won't cut it – the more the better. In an average-sized living room, you need at least five plants. Selecting the right plant for the room's light and humidity levels and looking after it well will further enhance its air-purification powers.
Those who have well-ventilated homes in non-polluted areas can still reap great health benefits from growing houseplants, but the rewards have nothing to do with air quality. Rather, the solid research on the link between mental health and the natural world tells us that being around plants boosts our confidence and mood and reduces stress. So, wherever you live, there's always an excuse to buy yet another houseplant.
Which houseplants purify the air?
A wide range of houseplants have the potential to clean the air. These are some of the easiest to grow:
*Parlour palm (Chamaedorea elegans) - A lush, leafy, slow-growing evergreen palm from Mexico, this withstands very low temperatures and low light (although it prefers medium indirect light). Height: 2 metres.
*Weeping fig (Ficus benjamina) - A gorgeous houseplant (or, rather, housetree) from tropical and subtropical Asia. It enjoys lots of bright, indirect light and humidity and sulks in cold, draughty rooms. Height: 3 metres.
*Golden pothos (Epipremnum aureum) - A vigorous evergreen from the South Pacific, this easy-to-grow trailing or (self-clinging) climbing plant is happy in low or bright indirect light. Height: 4 metres.
*Grape ivy (Cissus rhombifolia) - This evergreen climber uses tendrils to climb trees in the forests of Central America. An easy-to-grow, vigorous houseplant in medium to bright indirect light. Height: 3 metres.
*Aloe vera - A fleshy succulent from Oman, Aloe vera enjoys lots of bright, indirect light and very low levels of humidity. The evergreen serrated stems contain a sap that is often used to treat sunburn. Height: 60 centimetres.
*Mother-in-law's tongue (Sansevieria trifasciata) - This striking evergreen from Central Africa has upright sword leaves that thrive in lower humidity rooms in low to bright indirect light. Height: 75 centimetres.
*Peace lily (Spathiphyllum wallisii) - A fuss-free evergreen from the tropical forests of Columbia and Venezuela, bearing glossy, lush leaves and white spathes. Best in low or bright indirect light. Height: 50 centimetres.
*Corn plant (Dracaena fragrans) - This easy-to-grow evergreen from tropical Africa produces green flames of leaves atop sturdy cane-like stems. Best in low or bright indirect light. Height: 1.2 metres.
*Blushing philodendron (Philodendron erubescens) - An evergreen climber from the humid forests of Columbia, this is best grown around a moss or coir pole in a kitchen or bathroom in bright indirect light. Height: 2 metres.
*Moth orchid (Phalaenopsis) - These long-flowering epiphytes hail from tropical and subtropical Asia, where they grow high in the canopy of damp forests, making a bright bathroom ideal for them. Height: 50 centimetres.
