Whether on one-story structures or on skyscrapers, rooftop gardens are havens with a charm of their own. For the owners, they provide private worlds in which to grow plants and escape the bustle of city life. All this, of course, is made possible with soil brought in and carried to the top of the building for the pots and boxes that comprise the rooftop garden. If you have ever seen a penthouse garden, you know what a feeling of space it gives, especially if the building is high. It is like being on a mountain top, with a panoramic view that on clear days seems limitless.
Delightful as these skyline gardens are, they do present problems. The wind, for example, snaps trees and tears up plantings. Arrangements must be made to provide shelter in the form of fences or other barriers. These also give needed privacy. Winds constantly dry out the soil so that in summer when the sun is hot, plants often need watering two or three times a day. Pergolas, lattice fences,
wood panels, and laths can be erected to provide shade but still allow air and sun to enter.
Winter cold is another problem. In cold regions, where soil freezes solidly, evergreen plants are often windburned through loss of moisture that is hard to replace when the soil is frozen. The sun, too, draws off moisture and causes sunscald. Rooftop gardens only a few stories up are less affected by wind and are often easier to care for than plantings on the ground. They are usually protected by buildings on one or more sides and get sun for only a part of the day.
Roof Must be Strong
At the start make certain the roof is strong enough to support the weight of containers filled with soil. Modern buildings usually are, but you will be wise to have your structure checked by a building inspector. Then make sure that water can be drained away through pipes. Most important, build a wall around the edge of the roof high enough to serve as a guard. This can be constructed with some harmonizing materials such as concrete, brick, and wood.
The next step is to make a plan. On the whole, simple, formal designs are best in the limited area of a roof. Allow for some large boxes for trees and shrubs and for planters
or raised beds, which will give the feeling of flower borders. Erect fences and lay out several enclosed areas for dining, sunbathing, and reading.