A roof-garden cannot, of course, be adopted by every house-owner, but where the roof is flat, and access to it is possible, a roof-garden forms a very charming feature often with the special attraction of complete privacy. It makes an ideal place for sun-bathing.
The plan should be as simple as possible, and one seat at least should be provided, as, of course, the joy of the roof-garden is in its provision of a quiet resting-place.
In a very small space, rock-gardens have a special appeal, and if the roof constitutes the only garden, a rock-garden is the best kind to be made there. Almost numberless plants can then be grown, which will add greatly to its interest. If a roof-garden is made on a modern house, in a rural district, it will probably be on quite a different line, ie. it will be boldly but simply decorative, perhaps being limited to a few clipped trees or pyramid conifers, and one or two bright bowls of seasonal flowers.
Before setting about the construction of the garden, the makers must make certain what weight the roof can take, and the garden must be planned accordingly. Any heavy weights must be kept to the parts of the roof where there is most support.
The essential thing for success in a roof-garden is to secure good. “Virgin soil is best, and to this should be added decayed manure at the rate of one-part manure to ten-parts of soil.
This soil must be used to a depth of at least 6 in., and should lie over inverted turves, so that it does not either become stagnant, or get washed away down the roof-gutters. The methods of supporting this soil vary greatly. In a little roof-garden, it is probably best to use deep boxes or tubs only. The boxes can be especially made to fit, using I-in. Thick wood, or they can be merely deep boxes of any convenient shape or size, stood wherever desirable on the roof.
In a larger scheme, concrete or brick walls, 10-m. high, can be built to enclose the soil beds. Holes must be left here and there to allow surplus water to drain away, and some protection should be given over the house-gutters to avoid trouble from soil washing into them. (This, by the way, is of great importance while the garden is under construction, and loose heaps of soil or turf lie on the roof.)
On enclosed beds of soil, grasscan be made, if the roof is sufficiently large. Or bold bedding schemes can be planned, as in the larger garden.
Foror shrubs, however, deeper containers such as tubs are necessary, and these can occupy key positions in the roof-garden plan. A large roof rock-garden would be built on the lines laid down elsewhere, but with the base of the rockery built on a cement or brick enclosure similar to the ones used for formal bedding. Even a shallow pool or rill could, in some cases, be included in the same manner by the ingenious gardener.
In any case drainage is an essential factor to the success of roof gardening.
This is best secured by inverting turves at the bottom of the box or flower border. In the walls of the border, tear holes must be left at intervals of 6 ft. to permit the escape of water, and simple seepage drains of broken bricks about 2 in. in depth can be led to these across the border underneath the soil. The drainage material should be placed in position before the turves are laid over the surface of the roof. It cannot be too much emphasized that the secret of success in a roof-garden is to provide sufficient depth of rich, turfy soil, 6 in. being considered a minimum quantity.
On the roof-garden, protection must be given from strong winds, according to the position of the house. Trellis work forms an effective screen, and quick-growing climbers such as Climbing Knotweed, Wistaria, and Roses of the Wichuraiana type, can cover it, their roots being happy enough in a tub or deep box, if the soil is rich and well drained.