Privet (Ligustrum ovalifolium) - the small leaves make a compact, evergreen hedge
Early this year, I flicked on Radio 4’s Inside Science mid-review of recent research into the environmental benefits of hedges. Frustratingly, I can’t find the podcast now, but I believe the research was undertaken by the University of Surrey, and studied the effectiveness of green infrastructure (trees, shrubs and hedges) in reducing pollution concentrations in the vicinity of roads.
Researchers studied a number of roadside locations in Guildford, and found that hedges were the most effective green infrastructure for reducing pollution. Hedges were found to reduce exposure to ‘black’ carbon by up to 63 per cent, with exposure to ultra-fine and submicron particles also showing an appreciable reduction.
Having spent seventeen years working in transport planning, I’m well aware that green infrastructure can be unpopular with municipal authorities. Hedges particularly are costly to maintain; they can restrict visibility for road users and pedestrians, and cause a perceived reduction in security and safety.
However, as air pollution levels in many cities, Manchester included, often exceed ‘safe’ levels, the demonstrable benefits offered by hedges and other forms of green infrastructure shouldn’t be ignored: A primary school student from East Dulwich was interviewed by the BBC following the installation of 2.2m high ivy-clad green wall along the school’s boundary with an adjacent busy A-road. As an asthma sufferer, the student affirmed that he had previously been unable to play outside without coughing, but now could, due to the green screen.
The RHS are currently preparing a report on the benefits of hedges, appropriate species and optimal specifications, and I shall definitely report back here when it’s published, but here are a few considerations:
Evergreen species such as privet and holly offer screening benefits all year round;
Beech is a good deciduous choice as it holds on to its leaves throughout the winter, even when they are dead;
Hornbeam is also a good deciduous choice because it is fast-growing, and sometimes holds its foliage during winter;
Species with hairy leaves are particularly effective at catching and filtering out airborne solid particulates.
Given the government’s recent commitment to net zero emissions by 2050, clearly a far greater step-change is required than planting a few hedges. But if we all contribute by taking a serious look at how we use resources and travel, keep our private car use to a minimum and play our part in planting and nurturing our own green infrastructure, then collectively, we can make a difference.
Hornbeam (Carpinus betulus) - a fast-growing deciduous hedge