First Considerations in Rock Gardens
The creation of a rock garden is the attempt of man to create the natural rock formations found in mountains, where flowers grow in the crevices of rocks. If the man made version fails in rooting the plant, it will not make very natural appearances.
Any idea that these plants obtain food from the rock must be removed, as this is simply not a possibility. The function of the rock is twofold. They give us a natural suggestion for the environments in which the plants grow, and they conserve the moisture in the soil, giving the plants a supply of water in any weather condition.
This being known, the rocks we select for a rock garden should be porous, capable of holding a reserve of water. An impervious stone is better than none, as it will reduce the soil that is subject to evaporation. The soil in a rock garden must be well drained. The soil must be of a porous character and needs to be of a sufficient depth as well. Drainage is obtained by elevating the rock garden, and likewise sinking the floor below the surface level.
A well designed rock garden does not need to lavish with rocks, the spil bulk should be at least as large as the rocks. The placement of the rock garden needs to be removed from any formal environment, and you should do your best to imitate nature.
If your setting has many artificial accents, the illusion falls apart. It is also better to keep the rock garden away from grouping of trees, whose roots can find their way into the soil, exhausting it, and the leaves would litter the surface. It is best to mimic nature; you would not find lush trees is an alpine environment where the altitude is high.
Aspect must be considered once the rocks are in place. An alpine setting needs a sunny aspect, though this does not mean it needs full sun, as some plant do need some time in the shade as well. Rock gardens are great for creating variety, because you can consider the many aspects and needed exposure which is determined by the large variety of plants you can use in the rock garden.
The best material for a rock garden is sandstone. Often though, the gardener must be willing to take whatever material is available in the area. A hard, close-grained sandstone, granitic rock, or tuffa, limestone, and conglomerate will do. Soft stones need to be avoided, as they crumble away easily. 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 not be used in an Alpine Garden. Tree trunks hold mold and fungi, and can harm your alpine garden as well.