Chilling out in the city

They also provide a vital wildlife habitat.

The Steel City can boast perhaps as many as 120 such living "garden" roofs across the city.

And many more towns and cities – and individuals – are going down the green path, creating similar roofs for houses, offices and schools.

But what exactly do they grow where normally there is concrete or stone or slate? Research presented recently to an environmental conference in London, highlighted the merits of certain plants in helping to reduce temperatures in cities. One plant in particular, Lamb's Ears (Stachys byzantina) may be very important in the future.

A number of studies have shown the importance of roof vegetation in decreasing summer-time air temperatures. They achieve this by cooling surrounding areas through a plant's equivalent to sweating.

Royal Horticultural Society (RHS) scientist Dr Tijana Blanusa told the

World Green Roof Congress that Lamb's Ears significantly reduced the surrounding air temperature during early afternoon on a hot summer day, by some 1.5 degrees, for example, when compared with the bare, dry soil.

"Green roofs are not just about looking good," says Dr Blanusa. "There is much more interest recently in providing additional ecological and economic functions such as regulating internal building temperatures. But this research emphasises the potential in helping to reduce air temperatures. If only every building had a green roof and a green wall.

"With our climate getting warmer, gardeners will be playing an even more important part in helping to reduce the effects," she said. "Getting planting right in urban spaces, which as we all know can be very limited, is particularly important and can have a major effect in not only helping reduce urban temperatures but will also provide other environmental benefits." If you don't believe her, consider Sheffield's Sharrow School, whose green roof has been declared a local nature reserve. The 2,000 square metre green roof was designed to represent the variety of habitats found in Sheffield, such as Peak District limestone grassland, wildflower meadows, urban brownfield sites and a wetland area with a small pond. There is even a dead tree for birds to perch on and insects to burrow in. The roof also reflects Sheffield's distinctive landscape, with rolling hills and valleys made of locally-sourced recycled materials. Bird tables and insect feeders attract wildlife, and a weather station and webcam have been installed to provide research opportunities.

The Green Roof Centre organises "green roof tours" of Sheffield.

To find out more, contact Anna Cooper on 0114 263 6425 or email [email protected]

YP MAG 23/10/10