Scientists at the Royal Holticultural Society (RHS) and the University of Reading conducted a study that evaluated the ability of different of hedges at absorbing air pollution, comparing shrubs such as cotoneaster, hawthorn, western red cedar, privet, eleagnus and yew. The ability of such plants to absorb carbon dioxide can aid in global environmental issues such as air pollution, flooding, heatwaves and climate change as a whole as well as reducing the adverse health effects such as respiratory diseases that arise due to increasing air pollution levels. In fact, an RHS survey of 2,056 people found that a third were affected by air pollution!  Only 6 per cent of the sample were taking initiative in their gardens to reduce it.

Cotoneaster franchetii which is a dense, hairy and thick leaved bush plant with red berries was shown to be 20 percent more effective at absorbing air pollution than other shrubs on very busy and congested roads, but not significantly more effective at soaking up the pollution on quieter roads with less traffic. Just one well-maintained meter of the cotoneaster shrub can absorb the same amount of pollution that a car produces over a 500 mile drive in just seven days. Therefore, planting shrubs like the cotoneaster along busy highways and congested roads would be useful in an initiative to decrease the impact of air pollution. 

This is due to the fact that the leaf hairs and ridges on the cotoneaster increase the surface are that catches the particulate matter (pollution) and holds on to the particulate matter making it hard for it to fall off when the leaves are in motion.  The study also found that ivy wall cover excels at cooling buildings whilst hawthorn and privet help to alleviate heavy summer rainfalls and localised flooding.

Another significant finding was that common ivy (Hedera helix); Boston ivy (Parthenocissus tricuspidata); and climbing hydrangea (Pileostegia viburnoides)  has a beneficial impact on temperature and humidity when grown as building cover or as a ‘green wall’.  They were shown to reduce the air temperature internally and externally during the summer daytimes by at least 1 degree Celsius compared to buildings without any green cover.

 Common Ivy performed the best at summer cooling by reducing internal and external wall temperature by 7.2 degrees Celsius and 5.7 degrees Celsius respectively. Ivy was also deemed effective at lowering relative humidity during winter, with the relative humidity being 7.5% lower inside buildings covered in ivy.

References

https://www.theguardian.com/environment/2021/feb/18/experts-identify-super-plant-that-absorbs-roadside-air-pollution

https://www.independent.co.uk/news/science/pollution-plant-uk-roads-cotoneaster-b1803609.html

https://www.ecowatch.com/plants-fighting-air-pollution-2650611803.html?rebelltitem=1#rebelltitem1

https://www.rhs.org.uk/science/articles/ivy-homes

https://www.standard.co.uk/news/uk/air-pollution-super-plant-cotoneaster-royal-horticultural-society-b920236.html 

https://www.bbc.co.uk/newsround/56114125