The plants we live with

One of those two jobs is real. The other is a legend with a birth date, a 1989 space study misread for thirty-five years. Telling them apart is not pedantry. It is the line between decorating a room and deciding how to live in one.

Does a potted plant really clean the air in a living room ?

No. On this, for once, the scientific literature does not hedge.

The misunderstanding has a precise address. In 1989, the researcher B. C. Wolverton published a study for NASA titled "Interior Landscape Plants for Indoor Air Pollution Abatement". The context was space stations : sealed volumes, tiny, with no exchange of outside air. Plants were shut inside sealed plexiglass chambers, and three volatile organic compounds were injected, formaldehyde, benzene and trichloroethylene. Over several hours or several days, between 10 and 70 percent of the injected pollutants disappeared. The result holds. It simply says nothing about a flat.

This 1989 reference appears here because it is the historical source of the myth, not because it counts as current data.

The demolition job belongs to Bryan Cummings and Michael Waring, of the department of civil, architectural and environmental engineering at Drexel University in Philadelphia, writing in the Journal of Exposure Science and Environmental Epidemiology in 2020. They went back through twelve chamber studies, 196 experimental results in all, and converted them into the unit used to rate an air purifier, the clean air delivery rate. Median for a single plant : 0.023 cubic metres per hour. Brought back to the scale of a home, that means you would need between 10 and 1,000 plants per square metre of floor space to match what ordinary ventilation does on its own, for free.

Ten plants per square metre, in the best case. That is a dense greenhouse, not a living room.

What this shifts is worth stating plainly. If indoor air is a problem in a flat in Tunis or Casablanca, the answer is not botanical. It is mechanical and behavioural : bring in fresh air, cut the sources (combustion, cleaning products, tobacco, new materials), maintain the systems. The plant is not a filter. It never claimed to be one. That claim was made on its behalf, by the people selling it.

So what does living among plants actually do to us ?

Something, but on other ground : the body and attention, not the chemistry of the air. And the effect is smaller than interiors magazines promise.

The most useful synthesis comes from Ke-Tsung Han, Li-Wen Ruan and Li-Shih Liao, of the department of landscape architecture at the National Chin-Yi University of Technology in Taiwan, published in 2022 in the International Journal of Environmental Research and Public Health. It reviews 42 pieces of work, of which 16 enter the meta-analyses. What it declines to confirm is worth as much as what it confirms.

Two results come out statistically significant. The presence of indoor plants is associated with an average drop in diastolic blood pressure of 2.5 mmHg. And a positive effect is measured on academic achievement. On attention and reaction time, the two functions the usual talk plays up most, the authors find no significant effect. On brain activity measured by electroencephalogram, the variations lean in the expected direction and never cross the threshold of significance.

The authors list their own limits, and the list is heavy. Two or three studies feed each meta-analysis, which leaves statistical power low.

Participants are mostly students, a population that stands for very little. Grey literature was excluded, which opens the door to publication bias. A real signal, then, on an evidence base that is still thin.

So the honest sentence is this one. Living with plants is associated with markers of physiological relaxation. It is not a treatment, it cures nothing, and nobody serious claims otherwise.

Why the argument changes scale entirely outdoors

What is marginal in a living room turns decisive in a street. That is the pivot of the whole subject.

In Tunisia, the temperature gap between urban areas and the surrounding countryside runs to 3 to 5°C, according to figures relayed by the Tunisian Ministry of the Environment and reported by La Presse de Tunisie in August 2025. The phenomenon has a name, the urban heat island : a city overheating relative to its periphery, the work of concrete, asphalt, built density and missing plant cover. Three to five degrees, when the thermometer already reads 45, stops being a question of comfort.

The international literature exists, and it needs reading with care. A systematic review by Ahsana Nazish, Kiran Abbas and Emmama Sattar, bringing together the London School of Hygiene and Tropical Medicine, Aga Khan University and Ziauddin Medical University in Pakistan, published in BMJ Open in 2024, examined twelve studies that appeared between 2014 and 2022. Regions well supplied with green space show lower rates of heat-related morbidity and mortality. Urban vegetation lowers summer temperatures by 0.5 to 2°C in modelled scenarios.

Then come three reservations the authors state outright. Around 95 percent of the studies come from high-income or upper-middle-income countries, while vulnerability to heat is at its worst elsewhere. One study conducted in Hong Kong finds no significant effect. And the review does not allow a causal link to be established. The Maghreb, then, is not only short of trees. It is short of data on the trees it has.

How many square metres of green for a woman in the Maghreb ?

Few, and the shortfall can be counted. Tunisia has fewer than 3 square metres of green space per inhabitant in urban areas, against a World Health Organization recommendation of 10, while the lowest benchmark figures raised in Tunisian debate hover around 5 to 7. In Algeria, the most recent national inventory of green space, carried out in 2020-2021 and relayed by the Algerian press when a new green space law was adopted, puts the ratio at 4.16 square metres per inhabitant. In Morocco, the city of Casablanca has set itself the target of raising its ratio to 5 square metres per inhabitant by taking its green space from 400 to 2,000 hectares, according to L'Economiste.

These figures describe a very concrete inequality, and it has a gender. In societies where time spent at home and in the immediate neighbourhood remains, statistically, higher for women, a tree at the foot of the building is not an aesthetic question. It decides whether public space is usable for four months of the year.

Women are, as it happens, often the ones carrying the file. Alyssa Amara chairs the Tunisian association Zone Verte et Développement Durable, which works with the municipalities of Tunis and Ariana on urban garden projects, including a Japanese garden co-managed with the Japanese embassy and the Japan International Cooperation Agency. The urban planner Imen Zafrani Hioua argues for continuous green corridors inside Tunisian cities, using every available gap rather than waiting for large plots. In July 2026, however, La Presse de Tunisie described a national green space strategy whose implementation is slow in coming, against a background of citizen mobilisation against tree felling in Carthage.

The courtyard, the oasis, and the water they cost

Long before they became magazine motifs, the courtyard and the oasis were climate machinery. The riad, the dar built around an inner court, the Algiers patio all run on plain physics : thermal mass in thick walls that store the night's coolness, shade cast through the hot hours, and evaporation from water and plants that lowers air temperature by consuming heat. Work published in the Revue des énergies renouvelables of the Centre for the Development of Renewable Energy (Centre de développement des énergies renouvelables) in Algeria describes the patio as a buffer space whose microclimate stays more temperate than the outside air.

None of this is nostalgia. It is engineering, dropped in favour of the slab block and the air conditioner, a machine that cools one interior by tipping its heat into the street, and so worsens the heat island for everyone standing in it.

Then comes the tension nothing resolves elegantly : planting drinks water, in a region where water is the structuring constraint. Morocco's situation this year shows how misleading a respite can be. After years of drought that brought dam filling rates down to around 23 percent in February 2024, the season's rainfall lifted that rate above 70 percent at the start of 2026, against under 30 percent a year earlier, according to readings relayed by Le Matin and Lebrief. A wet year does not cancel a climate trajectory. It opens a window.

What that window allows is trade-offs, not slogans. Species suited to the local climate rather than imported lawn. Trees that cast shade rather than thirsty flower beds. Treated wastewater for irrigation, an option that the Tunisian green belt project, announced by the Ministry of the Environment to run from Sfax to the Algerian border, explicitly includes, with a restoration target of 260,000 hectares. A well-chosen tree is a water investment. An ornamental lawn in a semi-arid climate is a bill.

Something has to be given up in this story. The plant by the window does not clean the air, and no quantity of household foliage will make up for a mineral neighbourhood at 47°C. What it does is smaller and more honest : it lowers one blood pressure reading slightly, and it keeps the room inhabited by something other than us.

The rest is not settled in the living room. It is settled in what municipalities plant, in what they allow to be cut down, in how a building is oriented, and in whether a maintenance budget still exists three years after the garden was opened. Three square metres of green per inhabitant is not an ecology figure. It is an urban policy figure, and it is argued over where it is decided.

The Editors

The Sultane view