It's a sign of the times that roof gardens made their debut at this year's Chelsea Flower Show, as increasingly people are searching for much needed green space in urban areas.
 If you live in the city and think you may have a sustainable roof space, there are three Ws to consider, says Andrew Duff, director of the garden design faculty at the Inchbald School of Design in London. "The first `W' is weight. Make sure you can walk on the roof. You may not be able to put heavy pots on it, so before you can consider a roof garden you should consult a structural engineer, or if you are in the process of buying the property you can involve that in the survey. "If you are in a flat, find out whether you actually own the roof where you want to put the garden. It may be owned by the residents of the flat below." If you can't put much weight on the roof, sedum matting is a good way to green it up, he says. It's evergreen, stores water in the leaves and is succulent, and should only need watering during drought. Most of the time it will absorb enough water from the atmosphere and rainfall to survive. There's no need to add fertiliser or extra topsoil because these plants are conditioned to live in poor soils. The second `W' is water, as any roof is exposed to the elements. "You need to think about a water system because the roof is so exposed and water will just evaporate," says Duff. "Think about how you can recycle water off the roof and consider what plants will survive in dry conditions. Ornamental grasses such as Stipa arundinacea (pheasant's tail grass) do well." The third `W' is wind. "Wind is a huge issue on roofs," says Duff. "You need to source plants which will grow in really exposed sites. Small varieties of pampas grass are ideal. If you want to lay anything more tender, think about putting up a windbreak. Silver birch grow very well on rooftops. They are flexible and don't mind getting battered by the wind. But again you need to plan ahead for weight of growth. If you can put pots on your roof, choose plants which will withstand a lot of exposure, such as those which grow well on the coast. Look for those with small, tough, leathery leaves or grey foliage. Good examples include lavenders, sea buckthorn, griselinia (a dense leafy evergreen with upright habit) and santolina (cotton lavender), a shrub which looks its best during the summer months when it is covered with lots of tiny yellow flowers. The rest of the year its grey foliage provides good contrast. Ideally place heavy containers near load-bearing walls, or over a load-bearing beam or joist. As containers will dry out rapidly in the excess heat and wind, attempt to provide quite a deep container. Large plants should be well anchored to stop them from blowing over. Duff adds: "A roof is there to guide the water away from the building. Don't block the path of the water." | 
Travel, Entertainment & leisure
Professional Services
Health
Home Style
Home Improvements
Fashion & Weddings
Gifts
