When laying out a garden on a piece of sloping ground, one will almost invariably be confronted with the problem of what to do with the banks which of necessity will be formed. They are usually made into grass slopes, which are difficult to keep well trimmed, and are consequently apt to look untidy if labour is at a premium.
There is, however, a far better solution to the problem; the unwanted bank may be converted into a wall garden bright with colour and full of interest during the greater part of the year. The wall will enable the owner of a small garden, where there is no room for a larger rock garden on orthodox lines, to grow the ever-popular alpines and rock plants.
There is yet another use to which the "dry" wall can be placed, and that is to form a boundary for the formal sunk garden; in this case the wall will be quite low, rarely more than three feet in height usually less, and should be made of stones thinner and flatter than those used for the ordinary retaining wall.
The "Dry" Wall
The "dry" wall, as it is called, is constructed of stones usually sandstone or limestone from two to eight inches in thickness. They may be of any size within reason, and untrimmed. Stones are better than bricks, for they provide cooler and moister root-beds for the wall plants.
They should be bonded, that is, laid in layers so that the lateral extremities of a stone lie over the centres of the two stones in the row immediately below it. If the wall is to be over three feet in height, some means of strengthening the structure will be found necessary, unless very large stones are being used.
This may be done by the use of ties, i.e., long stones built endways into the wall with their ends penetrating the bank. These should be in layers; the individual ties being some six feet apart in the layer, and one layer eighteen inches above the other, care being taken to have the centres of the stones above between those of the ones below, or, in other words, the stones should be staggered. This structure serves to keep the wall secure and firm. The stones should be long in proportion to their height, and are best when their upper surfaces are flat or even cupped.
When placed in position they should be inclined slightly backwards, so that they are lower at the back than at the front, the larger and more weighty stones being kept at the base of the wall; the rain will then be collected and drained into the soil at the back of the wall to furnish moisture for the roots.
No cement is used, but earth is rammed firmly into the crevices between the stones, sufficient mould being used to keep the stones about one inch apart, vertically; the greater the slope of the wall, the greater the amount of soil that may be used between the stones.
This soil must be rammed well in to the back of the wall so that there is mould from the very front right though to the earth supporting the wall at the back. In addition, the earth should be well firmed after each row of stones has been laid, and no "air-pockets" must be left in the crevices.
Selecting The Plants
In selecting the plants the locality, climate, and aspect of the wall must all be carefully considered, so that suitable subjects may be chosen. It will be noted that the great majority of the plants suitable for the wall garden thrive best in the sun. A wall garden situated in the shade, however, can be made anything but drab and uninteresting For the shady wall in a cool position such hardy ferns as the Aspleniums, Polypodiums or the Phyllitis must not be overlooked.
Thus it can be seen that with a bit of thought and planning, a wall garden can be built by anyone, and will enable the gardener to enjoy hours of pleasure.
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