Gardening up on the roof

IMAGINE being cooped up in an office all day and then returning to your urban home and walking out on to a rooftop which has been transformed into a tapestry of colour, texture and calm.
Rooftop gardening can help combat climate change by lowering surrounding air temperatures, according to a recent RHS survey and, with this in mind, the organisation is encouraging urbanites to make the most out of their outdoor space and help the environment by growing plants.
"Getting planting right in urban spaces, which can be very limited, can have a major effect in not only helping reduce urban temperatures but will also provide other environmental benefits," says Tijana Blanusa, who undertook the RHS research.
Other benefits of green-roof gardening include heat-insulation, water-absorption, providing a safe environment for wildlife and soaking up pollution.
The RHS is showcasing two modern-style rooftop gardens designed by two rising stars, Hugo Bugg, RHS Young Designer of the Year 2010, and Melissa Jolly, winner of a BBC Gardeners' World 2010 award, at the RHS London Plant and Design Show on February 15 and 16.
Their designs are aspirational, but it's not impossible to create your own roof garden, whether you just want a few pots or a raised bed or two, or a more elaborate green carpet, providing your structure is secure. The RHS offers the following advice:. Before designing any addition to a property's roof check if planning permission is required.
. How much weight the roof can take? Large containers full of compost and plants weigh a considerable amount. There will be strict weight restrictions on balconies suspended out from the building.
. Check if the roof is waterproof, using the services of a chartered structural engineer or a surveyor. You may have to modify roof supports if the structural survey shows that support is insufficient.. Use an architect specialising in roof garden design for complex projects.
. Place heavy containers near load-bearing walls or over a load-bearing beam or joist as these can take more weight than unsupported areas.
. The main limitations of roof gardens and balconies are strong winds and sunshine. Take advantage of any existing protection, such as walls or fences, that provide shelter and shade.. Use slatted or mesh screens that simply filter the wind, creating a micro-climate for the plants within.. Containers will dry out rapidly in windy, hot weather so make sure they are a good width and depth.. Choose non-porous materials (plastic, metal and fibreglass) rather than terracotta as they reduce potential moisture-loss.. Ensure the container is lightweight and has ample drainage holes in the base.
. Some companies, such as Green Tech Ltd, offer a range of lightweight soils and composts suitable for roof gardening.. Use a layer of lightweight drainage material at the base of the container, such as polystyrene plant trays broken into 'crocks'.
. If weight is a consideration, fix the container down, so that it doesn't blow over in strong winds.
. Install an irrigation system where cost effective (in larger areas), ensuring excess run-off flows to a drainpipe outlet. In smaller areas, hand water as it's more accurate.
. Feed plants regularly. Controlled-release fertiliser in the compost is the easiest solution.. Top-dress pots annually replacing the top few centimetres with fresh compost.
. Liquid feed any annual plants used in plantings from May to September for best results.
GrowYourOwnCanefruit BARE-ROOTED cane fruits including blackberries, raspberries and hybrid berry canes can be planted up until the end of the month. You'll need to prepare the soil thoroughly by digging a trench along the proposed row and working in plenty of organic matter.