University of East London review finds no direct evidence that home gardens clean air pollution

Air pollution is one of the world’s most lethal environmental hazards. Approximately 99% of people worldwide live with air quality that does not meet safe standards.

Latest estimates associate polluted air with about one in eight deaths globally, putting its impact alongside established threats such as smoking and an unhealthy diet.

Gardens seem an obvious asset in tackling the problem: green, leafy spaces full of plants widely believed to remove contaminants from the atmosphere.

That assumption is understandable. However, a substantial new review suggests that the evidence supporting it is almost entirely absent.

Researchers led by the University of East London (UEL) looked for robust evidence that domestic gardens improve the air people breathe, finding remarkably little.

This does not show that gardens offer no benefit. Instead, it reveals that the question has scarcely been investigated properly.

Domestic gardens occupy substantial space

Gardens are not merely small fragments of urban land. The United Kingdom is home to an estimated 25.8 million gardens, covering around 959,800 hectares.

Their proportion of urban land differs considerably between locations. In London, gardens account for roughly 41% of the city’s total area, compared with about one-fifth in cities including Leeds.

Their extent makes this lack of knowledge particularly significant. Every day, millions of people use these spaces to unwind, cultivate vegetables and step outside through their back doors.

There ought already to be a large body of research examining how so much vegetation affects nearby air quality. Instead, the available evidence is extremely limited.

No direct evidence for home gardens and air pollution

The review was extensive. Researchers examined more than 34,000 studies and identified only 43 that considered both gardens and air pollution.

Despite decades of attention on vegetation in cities, none of those 43 studies directly tested whether a domestic garden reduces pollution or improves the air breathed at home. The total was zero.

“Most of us think of gardens as healthy green spaces, and they absolutely provide many important benefits. But when it comes to air quality, we simply don’t yet know enough,” said Dr. Karina Corada-Pérez.

“Plants can capture pollutants, but a garden is much more than a collection of individual plants. Its layout, boundaries, proximity to roads and buildings, and the way air moves through the space may all influence whether vegetation helps reduce pollution or allows it to accumulate.”

Why gardens are not the same as parks

The review makes an important distinction. Much of the evidence that trees, hedges and green walls capture air pollution comes from parks, street canyons and other larger green areas, rather than private gardens.

In these environments, tree cover has lowered concentrations of coarse particles by between 7 and 24 percent.

Domestic gardens function differently. Houses, fences, sheds, parked vehicles and varied planting can all alter airflow, producing conditions absent from more open green spaces.

In some circumstances, dense vegetation could even hinder cleaner air. Although thick planting may collect particles on leaves, it can also hold stagnant air in the area behind it.

Some findings from wider research remain encouraging. A small number of studies found that roadside hedges and green walls cut nearby particle pollution by more than 70 percent.

However, outcomes differed greatly according to elements including the vegetation’s height and spacing, along with weather conditions.

Growing food beside busy roads

The review also considers those who grow food at home.

Fruit, vegetables and herbs cultivated near heavily trafficked roads can absorb pollutants carried from passing vehicles, potentially transferring them to food.

Metals are the principal concern. Previous research detected lead accumulating in crops grown within around 10 metres of heavy traffic, in some cases exceeding European safety limits.

The type of leaf appears to affect exposure. Parsley and mint generally collected more contamination than root vegetables or legumes, which was associated with their broad, uncovered leaves.

This is not a reason to remove vegetable beds. The authors emphasise that growing food at home remains worthwhile, while calling for more precise advice about where and how to plant.

Plant selection is not straightforward

Choosing the “right” species is more complex than it might appear. Leaves with rough, hairy or waxy surfaces often capture particles effectively.

Thick conifers may be particularly good at holding fine particles because of their needles and evergreen foliage. Nevertheless, the same plants may bring less obvious drawbacks.

Certain plants emit natural compounds that react in sunlight, contributing to secondary pollution during hot weather. Others produce highly allergenic pollen that affects people with hay fever.

Routine garden maintenance also has an environmental effect. Mowing, pruning and using petrol-powered equipment can all create emissions or trigger the release of plant compounds.

Building evidence from real gardens

Instead of offering planting formulas, the paper calls for evidence collected in actual domestic settings.

It argues that guidance based on parks cannot automatically be assumed to apply within a back garden’s boundaries, where air circulates according to its own complex patterns.

“Because millions of people spend time in their gardens, grow food in them and open their homes onto them, we urgently need research in real domestic gardens,” Dr. Corada-Pérez said.

“Only then can we give homeowners, planners and policymakers reliable advice about which planting choices are most likely to support cleaner air.”

“Domestic gardens already support biodiversity, help cool our cities, reduce flood risk, provide space for growing food and improve our wellbeing.

“Understanding how air quality fits alongside those benefits could help us make better use of one of the most widespread – but least studied – forms of green infrastructure in our cities.”