Garden Rockery Stones for Your Rockery Garden
The rockery gardener is faced with a wide choice of stones, but they all fall into two basic types: sandstones and limestones.
Sandstones and Slates
Sandstones were formed over millions of years as successive deposits of silt hardened to form layers, or strata, of stone. When cut, sandstone splits vertically, along ’vents’, a process which can also occur naturally as a result of upward pressure; and horizontally, along the lines of the strata. See figure 1. They are thus easily cut into block shapes of various sizes.
These blocks may be used for makingas they can be laid, layer after layer, like the dry stone walls surrounding farms in some stony areas.
Slates are sandstones which developed on the earth’s surface but were eventually buried many thousands of feet below it, forming under the terrific pressures, very thin wafer-like structures.
When placed on their edges slates are very brittle but if laid horizontally they create exceptionally strong structures.
Sandstones and slates can be found in:
- Millstone Grit
- Cornish Slate
- Welsh Slate
Limestones may be formed in a similar way to sandstones but more usually they derive from the crushed bodies of vast numbers of crustacean insects and vertebrate animals which, under pressure for millions of years, form into irregular layers of stone.
With careful selection these asymmetrical stones can be made to fit together like a jigsaw puzzle, or used to create a series of layers at different levels, with scattered pockets ofbetween. They are excellent for use in screes either singly or in twos or threes.
Limestones are quarried in the following parts of the UK:
A form of limestone called tufa stone deserves a mention here. It is a light porous stone, ideal for limited spaces as it enables you to grow many small plants, both in the stones and the soil beneath them.
The surface is quite soft and can be punctured with holes, cut out with a hammer and chisel or a drill. The holes, which should not be too wide, are ideal for supporting the young seedlings or rooted cuttings of any alpines requiring good. A plug of mortar (five parts of sand to one part of cement) pressed on two-thirds of the soil surface in the holes after planting, will ensure that the plants and the soil will stay put and be less likely to dry out.
You can use an old-fashioned potato peeler for sliding the seedling into the hole and a ball-point pen for ramming the soil in after it. A potato peeler is also useful for weeding in the tufa blocks.
Do not use any stone formed volcanically in the United Kingdom, that is marble or Aberdeen granite, as these have the wrong character for a rock garden or for wall building.