The rock garden is man's attempt to imitate the natural conditions of Alps and mountains where flowers are rooted in the crevices of rocks. If it fails in this, its principal function, how can it serve its purpose as a home for the plant?

The idea, not by any means uncommon with those who have not looked closely into the question, that there is some magic virtue in the rock itself by which these plants obtain food suitable for their needs, must be abandoned.

The function of the rock pieces in our alpine garden is twofold. They serve to give us a suggestion of the natural environment of the plants we wish to grow, which is good; but, better still, they conserve the moisture in the soil, and thus ensure that the plants have a constant supply of it in all weathers.

This being so, it is well to select our rocks from material which is porous, and therefore capable of holding in its substance a certain reserve of moisture. Yet an impervious stone is better than none, as it reduces the area of soil subject to evaporation.

The next point to understand is that the soil in our rock garden must be well drained. This may be attained by ensuring that it is of a porous character and of sufficient depth. Drainage is assisted by elevating the rock garden, or, what comes to the same thing, by sinking its floor below the general level.

It is not necessary to be lavish with rocks. In a well-designed rock garden the soil should bulk at least as largely as the rocks. The position of the rock garden should be as far removed from a formal environment as possible. It is, or should be, your best attempt to imitate a piece of nature.

If it is associated with walls, greenhouses, or other artificial surroundings the illusion falls to pieces. It is better also to keep it away from the neighborhood of trees, whose roots would find their way into the soil and exhaust it, and whose leaves in autumn would sadly litter its surface. Moreover, it is well to be consistent in our mimicry, and to remember that the landscape is innocent of trees at the altitude where alpine flowers thrive best.

Once you have satisfied the conditions of rocks and the position of the garden, you have to consider another important factor – aspect. The alpine garden should have a sunny aspect, though this does not imply that every part must enjoy full sun; nor would that be desirable, since there are plants which will thrive all the better in shade or partial shade.

One great charm of the rock garden is its variety, and that can best be maintained by providing all the conditions of aspect and exposure demanded by the various plants available for our purpose. What materials are best in a rock garden?

Perhaps the best material for the purpose is sandstone, which incidentally is a preferred material for large fountains as well. In most cases though, the gardener has to be content with what is most easily obtainable in his district. A hard, close-grained sandstone, granitic rock, or tuffa, limestone, and conglomerate will do. Soft stones which crumble away under weather influence are obviously unsuitable. If natural stone is unprocurable, or the cost is too expensive, then the gardener must make shift with brickyard waste, but he should select that which is porous.

Clinkers, vitrified brick fragments, dressed stone blocks, portions of decayed statuary, lumps of alabaster, minerals, and sea-shells should never be seen in the alpine garden. Tree stumps also should be avoided, as they harbor fungi to the detriment of the plants.

The stone pieces should not be too small or too uniform in size. Good bold pieces up to the largest size the gardener can conveniently handle should be procured, and by preference they should be quadrangular, though only very roughly so.