To be a success a rockery (rock garden) must have adequate. Dig out the site to about 2 ft. and fill with stone rubble and peat. On this build gradually, layer by layer, with good soil having a percentage of sand, loam and grit worked in, so as not to leave spaces. Gradually reduce width and breadth of layers to secure a good angle of slope. Arrange all rocks (stones) very carefully, using several at a time rather than isolated specimens. Bury a fair bit of each stone and it should always slant into the soil, not outwards. Do the job thoroughly, as if the stones are piled anyhow and the soil not well packed in, the weathering will silt the earth down so that the will come across soilless cavities. All outcrops should be laid at the same angle, following the grain or line of stratification, I.e. like the outcrops on a mountain, otherwise the effect will resemble a mad dream.
Choosing the Stone:
Where local stone is available, this will obviously save very heavy transport charges which are inevitable if, say, Westmorland limestone is sent from the Lake District to Hampshire. Granite, though often recommended, has a cold, somewhat funereal appearance and is hardly sufficiently porous. Surrey or Sussex sandstone, similarly the brown sandstone known as Kentish rag, are good, but some sandstones are easily broken down by frost. Note that sandstone is generally quarried and it may be some years before it is fully weathered by rain and frost. Weatherworn limestone from Westmorland, northwest Yorkshire or the Mendip Hills in Gloucestershire can be strongly recommended. It is mostly greyish blue in colour. Purbeck rockery stone from Dorset is a good buff-coloured quarried rock which is often a little cheaper than weathered limestone from the north. The ideal rock garden site is one facing south-west; due south is less satisfactory as the soil tends to dry out more quickly in hot weather. However, almost any aspect will do provided it is away from overhanging trees and draughty positions near walls and buildings. Rock gardens can be made on the flat, when a main path is usually made to slope down to about a couple of feet, with subsidiary paths sloping in similar fashion. Where possible, paths should be made of finely broken stone, of the same type used for the rockery proper.
The Scree or Moraine. In Nature the terms ‘scree’ and ‘moraine’ have different meanings, in horticulture they are almost synonymous. They refer to a special bed in the rock garden which is specially made up of grit, plus a little soil and peat ormould. It is designed for plants which prefer very little humus, sharp drainage and refuse to tolerate the least suspicion of winter wet. Such a bed is often termed a moraine if supplied with water from below, and a scree when it is watered in the normal way from above. Watering from below necessitates inserting a pipe length at the highest point of the bed and, of course, connecting it to the mains with a tap to turn off the water as necessary. This method is, however, less popular nowadays and a bed 2 ft. deep with about 6 in. of stone rubble below for drainage is favoured.
The scree should be made at the same time as the rock garden proper, choosing a low level, with rising outcrops.
Note that if lime-hating plants like Gentiana sino-ornata, Phlox adsurgens, Sanguinaria canadensis and dwarf, are chosen, the scree should be watered with rain-water. Among the many plants which do not object to lime, all of which do well in a scree, are: Acantholimon.
Ranunculus amplexicaulis Omphalodes luciliae
These can be used to ‘break up’ the stones and rock plants. Note that an alpine lawn does not consist of dwarf grasses, as these would eventually smother the plants that are an essential feature of the lawn. Thymus serphyllum and its varieties, also Antennaria tormentosa, are planted about 8 in. apart to produce a close, evergreen ‘lawn’ which can then be furnished with a wide variety of rock garden subjects including dwarf-growing shrubs and bulbs. These must, of course, be chosen carefully so that they are not smothered by the thymes or antennarias. Any of the following would suit:
Pulsatilla vulgaris (pulsa-
Juniperus sabina tamariscifolia.
Linum narbonnense gentianoides
Plants for the Rock Garden Proper:
The choice is very wide and only a brief selection, including dwarf shrubs and bulbs, is given below. Descriptions and notes on cultivation may be found alphabetically in this work. Enthusiasts should consult catalogues issued by nurserymen specialising in rock plants. Note that the term alpine in its proper context means a plant growing wild on a mountain but gardeners use the word to cover any plant suitable for growing on rockeries or in rock gardens. Experts reject hardy and half-hardy, considering they are out of place in these surroundings!