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Bulbs and Kindred Plants
Rock garden design
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Home garden design > Wall-garden Pockets
How often do we pass a wall constructed of native rock which the elements have ruthlessly trodden into form and ask ourselves why it has such an indescribable charm.
This is especially true of an old dry masonry wall which holds within its shadowy nooks the echoes of history and which is greatly enhanced not only by the proper setting but by the tiny plants that are mothered in the crannies between these gray boulders. Now and then along the roadsides in New England do we find a stone wall; the lines of which are softened by friendly touches of the Virginia Creeper (Ampelopsis quinquefolia) or Bittersweet (Celastrus scandens). It is not uncommon to find a sturdy little cedar pressing close to the cheeks of these rugged rocks, protected against the north winds, its deep green adding beauty to the wall at all seasons. We cannot deny that Nature's planting, humble, simple, and limited as it is among the stones, has done much to give this wall distinction.
With some of these examples of planting by the Great Gardener, why should not man attempt to copy and also to improve on a newly constructed wall and give it at least some of the charm that may be found in the old walls ? At first thought one might consider it a waste of time, as well as impossible, to try to break or soften the lines of these new but rugged-faced gray rocks with interesting touches of colour. It is not only possible, but one of the most fascinating adventures in our garden world.
There is truly a charm in the arrangement of these little plants in the crannies of the rocks which respond by lavishing upon us not only their seasonal bloom but the most delicate fragrance. We do not have to depend on flowering plants to complete our wall-garden picture because Nature has provided some timid but sturdy varieties of Ferns which will not only remain green and fresh through the summer's hardships of drought but will always make an interesting study as they point their feathered fingers at us when we pass.
In order to get the best results, one should keep in mind certain principles, for there are no arbitrary rules of planting.
It is quite important that the retaining wall should be on a slant, the base of which may be from three to four feet wide. The foundation should go down to solid ground or from two to three feet in depth. If the bank above the wall is high and the thrust bound to be great, it is advisable to use mortar or concrete in fitting the foundations.
Large stones used for the base of the wall resist alternate freezing and thawing. The foundation should be from two to three feet below the surface, depending somewhat on the height of the wall and also on the thrust back of it. These base stones may be fitted at right angles to the length of the wall and in this way the foundation structure is bound to resist considerable pressure from the hill or terrace back of it. There is no need of a mason to construct your wall from the surface of the soil up.
It is not a good practice to allow the stone to reach the cut face of the bank, especially if the soil is poor. Leave at least from four to eight inches between the bank and the wall. This space should be filled in with a rich garden loam consisting of one fourth well-decayed cow or horse manure, one half garden loam and decayed sod, and one fourth decayed leaf mould. This soil will not only hold the much-needed moisture but will furnish plant food for the rock plants for many years.
If there is danger of drought, one may fit a one-inch galvanized pipe, perforated with a small hole every six or eight inches, which should face the wall. This pipe may be connected to the water supply, and with a valve, one may, at needed periods, supply the water to the roots of the wall-garden plants. With this pipe from twelve to fourteen inches below thesurface, it is out of danger of freezing. It should slant slightly upward from the valve, and before winter sets in the water may be drained off. The one drawback with this underground system of watering is that in four or five years the pipe is rusted out, no matter how well it is galvanized.
If you are fortunate enough to have the privilege of deciding on the site of your wall garden, select the south, southeast, or southwest exposure. If you decide on any one of these exposures your plants will get the sun and be protected from the north winds as well. In constructing the wall above the surface soil, the outer face of the wall should be left rough with the stones fitted in such a way as to catch the moisture. It is an advantage to the plants to fit them into their limited space by spreading the roots out over a layer of soil and then fitting more rich loamy soil over the roots. Frequently, small stones are used on each side of the plant to prevent the stones above from crushing them. These pockets should always slant downward toward the embankment, and this construction will direct the moisture toward the root system. There must always be sufficient space to support the normal growth of the plant if the desired effect is to be looked for.
Seed may be planted in these crannies if the soil is loosened in the spring, a little sphagnum moss placed next to the seed, and then a layer of soil on the surface. This material should be kept moist until the seed germinates and the seedling becomes well established.
If sprinkling is resorted to, it should be done in the evening and the water applied in the form of a fine spray so as not to wash the soil out of the space between the rocks and expose the roots of the plants.
It is good taste and also practical to connect the retaining wall with the slope above by planting rock plants that will feel their way to the edge and hang over. For the edge planting, dwarf-growing plants similar to those fitted into the spaces between the stones will give a better effect than tall-growing sorts.
If one is to treat a brick wall, the only satisfactory method is to use espaliers of bamboo so constructed that the trained fruit tree, Rambler Rose, or vine may be at least two or three inches away from the wall. This prevents rubbing, gives the proper air circulation, and prevents many insects from destroying the plants. Brick is seldom used in constructing a retaining wall and therefore is never planted to rock plants.
The wall may be connected with its surroundings by planting along the lower edge and allowing the plants to fit themselves in a natural but uneven fashion along the border. Walls of stone, brick, or even concrete make a charming background for the perennial bed and therefore should be constructed wherever practicable.