Zahrah Nasir shows how you can turn your rooftop into a green paradise

Creating and successfully maintaining rooftop gardens on flat areas of the roof is, in many respects, quite a different proposition from growing plants, edible and otherwise, in an area of actual garden ground. But as long as certain basic principles are kept in mind, with a liberal dose of added common sense for good measure, a rooftop garden can be a veritable paradise indeed.

First and foremost is the need to establish if your house roof is structurally suitable to take the extremely heavy weight of necessary containers, pots, earth (wet earth is surprisingly heavy), plants and other assorted accoutrements associated with working on, and then being able to relax in, your rooftop retreat. Discussing the issue with the original architect of the property is ideal but, where this isn’t possible, then taking the advice of another architect or experienced building contractor is a sensible step as you most certainly do not want the house roof to crack, cave in, or for the ceilings below to be damaged by water seeping through.

Also of high importance is the amount of exposure to direct sunlight and wind the roof is subject to at different times of the year as, according to this, it may be necessary to incorporate firmly fixed shade and wind protection barriers before the space is suitable for the cultivation of plants. It is, of course, possible to use shade giving, dense foliage, climbing and rambling plants, growing over strong frames and trellises for these purposes, with the varieties of plants suitable for such use varying depending on the region in which you reside.

Rooftop gardens tend, due to exposure, to require more water than gardens on the ground as the plants receive more sunlight and the pots, walls and the roof itself all soak up heat during the day and radiate it out at night, therefore, a convenient water source is of immense importance as, if at all possible, is an on-the-spot water storage facility for those times when load-shedding prevents the pumping up of water from other sources. Rooftops are correspondingly cooler too, over the winter months, and tender plants may require extra protection from low temperatures and cold winds which their more sheltered ground level companions may not require at all.

Rather than have dozens of heavy clay pots scattered around, it can be more sensible to create some form of raised garden beds on the roof, their length and width sensibly distributed over main, load-bearing, construction beams. Such beds can, if structural waterproofing is sound, be laid directly on the roof itself although it is, of course, still necessary to incorporate some form of drainage into the bed so that any runoff water, from watering or as a result of rain, has a place to escape. Raised beds can also be constructed standing a few inches, even a couple of feet or more, above the actual roof level.

They can easily be made out of wood or by securing planks around the edges of old tables with holes drilled through the table top for drainage or even on top of a charpoy base. Such raised beds, with planting depths varying from four to eight inches, are ideal for a whole host of flowers, vegetables and herbs although climbers, grapes for instance, need containers with a soil depth of 18 inches or more.

Other good ideas for rooftop containers, keeping weight in mind, are heavy duty buckets and bins of all sizes, half drums, lined baskets and just about anything else you can think of — giving recycling of unwanted or broken household items priority over going out and purchasing new containers to use. Always keep the end weight — this being container full of wet earth and plants — in the forefront of your mind, plus, whenever possible, distribute heavy weights all around the rooftop rather than concentrating them in one place.

All plants that can be garden grown, except for full-sized trees, can, with the correct care and attention, be successfully cultivated on the rooftops of houses and small blocks of apartments but growing an Eden on top of a high-rise building usually requires different techniques although, in a major effort at greening up cityscapes all over the world, high-rise gardening is being increasingly incorporated into all sorts of structures with even orchards now being cultivated way up in the sky.

Please send your gardening queries to zahrahnasir@hotmail.com. Remember to include your location. The writer will not respond directly by e-mail. Emails with attachments will not be opened.