How to Create Interesting Rockery Gardens

Colour in the garden is not just a matter of choosing flowers. Apart from foliage, berries and the bark of trees, the colour and texture of stone creates an atmosphere of its own. This applies particularly in the rock garden, where you can create a cool or cheerful effect by the use of stone in combination with plants. For instance, a rock garden made with yellow or red sandstone and screes covered with the bright green leaves and gay flowers of the saxifrage family would be a warming sight on a sunny day in spring. On the other hand, by setting a greyish sandstone in large slabs and interplanting it with dark-green conifers and evergreen shrubs, a distinctly sombre scene would be created.

Limestones are often favoured for rock gardens. Some are grey, others yellow or brown, just as sandstone may be anything from yellow to red or green. Kentish rag from the lower greensand beds has good colour, but Portland stone is apt to look a little dreary. Quite a reasonable colour can be made by staining cement with a solution of iron sulphate and, by making your own rocks you would be able to decide on the shape and size by making your own moulds. Tufa, which weathers to a dark grey and is a soft absorbent rock like pumice stone, can be replaced by ‘hypertufa’. Tufa is a good home for plants like the mossy saxifrages, but owing to its expensiveness a substitute may be made by mixing two parts peat with one each of sand and cement (all by bulk). The materials must be thoroughly mixed before water is added though the peat should be moist. It is usually best to mix the water in until a thick cream cement is formed. It should be poured into specially prepared moulds made by digging large holes in the garden and lining them with large rocks or stones. When the ‘hypertufa’ has dried the other stones may be knocked out easily with a hammer or left. Pockets for plants can be cut with a chisel or formed when the mixture is poured into the moulds. Cement colorants can be mixed in when making the ‘hypertufa’.

Granite was used in the Victorian era for rock gardens, and though it is expensive its crystalline qualities make it attractive. It may well become popular again with changing fashions in design. In former times rock gardens were conceived in the form of dells with running water and  ferny niches. In the early 1900s greater interest began to be shown in simulating the actual conditions-»of alpine regions to provide suitable conditions for the growth of alpine plants. Your choice will probably reflect your approach: that of an enthusiastic plantsman or that of a gardener seeking to add another feature to the garden to contrast with the flat lawn or to act as a focal point.

The rock garden with pergola.

Image via Wikipedia

A lot of nonsense is talked about the importance of obtaining rocks which fit in with local rock formations. Unless the local rock formations are visible and contiguous with your garden this would hardly seem to matter. More important is the fact that if you obtain rock from some distance away the price per ton is likely to be three or four times as high as it would normally be to pay for transporting it. A ton of stone can be had for a few pounds and a ton of sandstone would be enough for a small rock garden. Remember that the volume of a ton of rock will vary. The same volume of some limestones will be twice as heavy as sandstone.

Limestones and sandstones show varying degrees of stratification, which makes them easy to lay out if in placing them the lines of stratification follow nature. Generally, in designing rock gardens the rocks are laid as though they formed part of a natural outcrop, and this is a good system to follow. If you have a sloping garden it is easy to set rocks in the slope to make a rock garden. The rocks should themselves slope backwards so that the rain falling on them runs back into the ground and not down the hill. If your garden is on the flat the easiest procedure is to dig out a hole to make both a mound for the rock garden and a site for a pool at the same time. It is also quite feasible to build a rock garden on the flat with long flat pieces of stone sloping slightly upwards. Interspersed with an occasional tall conifer of the cypress family, fine horizontal and vertical effects can be obtained. The main reason for the slope in a rock garden is to achieve the extra drainage needed by many rock plants, and this can be obtained without either rocks or a slope by making a raised bed using railway sleepers or concrete slabs. If you have a garden sloping towards the south you have the ideal site.

If, owing to the flatness of the soil, you are worried about the drainage it is best to dig out the soil and put in a central base of rubble, broken brick, coarse gravel, and so on. If the soil is a heavy clay it will be necessary to mix grit and sharp sand with it when returning it to the site. How you set the rocks will depend on their shape and the number available. A large number of flat stones will enable you to set one on top of the other with gaps and crevices for smaller stones and soil in the style of an outcrop. If you are dealing with a smaller number of block-shaped stones it will be a simple matter to set them out like ramparts to form small compartmented terraces of soil. If you are including a pool in the design you may like to incorporate a water course together with a submerged pump to pump water from a pool on a lower level to one on a higher level. Such a system will require an electrical supply to work the pump and mains water supply to keep up the level of water lost by evaporation.

If you are building terraces you have the basic requirement for constructing a scree. A scree is simply a pile of broken rocks and so on at the foot of a steep cliff. It is ideal for certain alpine plants which require dry conditions where they meet the soil. Dig out about 1-2 feet of soil and put in a layer of small rocks at the bottom a few inches thick. Over this lay some fibrous material such as sphagnum peat to prevent the topsoil penetrating the drainage area, and then cover this with a top layer of chippings,  gravel,   peat  and   loam  and finely broken down leaf-mould. The stone chippings and gravel should form four fifths of the total bulk.

If you are incorporating running water in your rock garden you can also construct a moraine which is simply a pile of stones at the foot of a glacier, on which many fine-flowering plants have been found to thrive. The moraine is similar to the scree except that the bottom of the excavated area and halfway up the sides are lined with puddling clay or cement to make an underground lake. An outlet is made at the lower end of this lake a few inches above the level of the bottom, and layers laid down as above for a scree. Water is let in at the upper end of the slope. It is important not to try to grow lime-hating plants in a moraine or scree made with limestone chippings.

Soil for the rock garden is best made of four parts loam, two parts humus and two parts grit. The best loam is made of properly matured fibrous turves, but for most gardeners’ purposes it may be thought of as a good garden soil with both good drainage and moisture retaining constituents (sand and clay). The humus may be provided by peat, compost or leaf-mould. The grit should be sharp (not builder’s sand).

The use of plenty of loose granite or limestone chippings on the surface makes for an attractive appearance, keeps down weeds and helps to retain moisture. Chippings should be added to screes and wherever there are poor-soil loving plants. 

07. September 2011 by admin
Categories: Rock Gardens | Tags: , , , , , , , | Comments Off on How to Create Interesting Rockery Gardens


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