You can make a rock garden anywhere. This may sound like nonsense to a gardener of experience, but it is perfectly true. If you are prepared to accept whatever limitations the site may impose, you can have your rockery in any part of the garden site you wish. It may even be the principal feature of your garden.
What do you want of your rock garden? Do you want the kind of rock garden you see at exhibitions, where rocks are arranged in picturesque fashion and every available ledge is smothered with a, carpet of colour? If so, you must make it in a very open, sunny site. Do not plan to have this brightly coloured kind of rock garden in a damp half-shady corner of the garden, where ordinary borderdo not thrive; the brilliant splash of colour you desire just won’t happen. Such masses of colour only come in response to bright sunshine.
Let us consider for a moment some possible types of rock garden for special sites. First the colourful rock garden, made on an open sunny patch of ground.
The site may be either sloping or flat, since various levels will be arranged artificially in the course of construction. It is also possible to arrange for pockets—or ledges—of soil with a variety of aspects, and even to arrange for deep shade in parts of the rock garden, by careful disposal of the rocks. An openis the ideal one for the rock garden to occupy, because it can be made a home for so many different kinds of plants.
An existing sloping bank or banks, perhaps with only a moderate amount of sun, means planning rather a different type of rock garden. Often it is more convenient to use such a site, in spite of the partial shade, than to begin on a flat site, where all the labour of excavation and building up must be done. A rock garden in partial shade, particularly if running water can be introduced, can be made to look very charming and natural. Some, carefully selected for their capacity to flourish in shade, would find a home in this type of garden. Its character is intimate rather than spectacular.
Then there is the type of site which, queerly enough, is just the one that many inexperienced gardeners choose for the feature—the site in entire shade, and right under the drip of trees. There are few rock plants—few plants of any kind—that really thrive in these conditions. Ferns, and a few shrubs such as periwinkles,, and St. John’s wort, and such perennials as lily of the valley, Solomon’s seal (polygonatum), ramondia, and cyclamen are at home there; but the list of possible plants for such a rock garden is easily exhausted.
Finally there is the problem of cultivating a few rock garden plants that are special favourites, in a formal garden where an ordinary rockery is out of the question. Little rock gardens here can take the form of dry walls between various levels, bordering the sunk garden or supporting terraces; or rock work of a rather informal type can be introduced at the sides of steps, without unduly destroying the formality of the design. The spaces between paving stones provide another place where rock plants can be grown without introducing a rock garden of the accepted type. Rocks on a sloping bank should be arranged so that they leave pockets of soil for planting.
Having examined the allotted site for the rock garden, or having selected the site from among two or more alternatives, we can still choose between several different styles. Since rocks occur in a natural state in all sorts of districts, and at all altitudes, the term rock gardening must not be limited—as it so often is—to the rocky hillside, or alpine garden.
Exquisite examples of natural rock gardening occur in such districts as the limestone valleys of Yorkshire. There the water from the hills runs among and through the limestone, forming channels, sometimes on the surface and sometimes below the ground. Where the water emerges at the surface and wears its way through the rocks, they become waterworn to curious and picturesque shapes, and the surface streams carryingand soil as they tumble to the lower plains gradually clothe the watersides with plants and of many kinds.
This type of rock and water garden can be imitated in quite a small garden if (a) a water supply exists or can be introduced, and (b) if some arrangement for the disposal of surplus water is made.
Cost probably enters into the first requirement, but it might be remarked here that cost is not very great after the initial expense of installation, even if company’s water is used. Cost can be reduced by using the same water over and over again, which means the use of a small power pump, costing from two and a half guineas upwards.
It can also be reduced by using the merest trickle of water, in the form of a small cascade, the water descending from pool to pool down the rockery slopes. Also in this type of garden the water can be turned off except when the garden is in use for reasons of economy.
With regard to the disposal of surplus water, local circumstances must dictate procedure. Where no open ditch or main drain can be used, a small amount of such surplus water can be very easily disposed of by the sump method. For this a deep hole is excavated in some part of the garden to be occupied by shrubs or lawn. The hole should be at least four foot deep, and proportionately wide, and into the open hole should be thrown rough, porous clinker or other material of this character. The soil can then be returned to make the surface as before, and either turf or shrubs should be used over the sump. Turf is preferable in many ways, but chiefly because should the sump ever, in future years, become ineffective, as it might if the soil silts down and consolidates, it could be opened again, and fresh clinker used.
Naturally only a small surplus can be disposed of in this way if the surrounding soil is of clay; but if the garden has a porous natural subsoil, the sump will take much more. Pipes would, of course, have to be laid when the sump was built to take to it the water from the lowest end of the rock garden, unless a marshy edged pool were arranged. Such a pool, overflowing into the surrounding soil, should be set below the general garden level, and a sloping trench, filled with clinker, led from this to the sump.
Another type of rock garden imitates a rocky cliff such as is seen at the seaside or in mountainous districts. Here the surface crust of the earth has crumbled away, leaving a cliff more or less vertical in form. The rocky cliff surface continues to crumble, and as it does so, the finer particles are here and there caught on ledges. Birds carry seeds to these ledges, and the result is a picturesque, colourful bank in the steep cliff side, which can be imitated artificially but, if carefully done, very effectively in the garden.