Building a Rock Garden - Plants, Rocks and Design Ideas

Rock Beds

Where there is insufficient space for building a rock garden or it is not desired to have such a feature but still to grow rock garden plants, a rock bed provides a very attractive alternative. Such a feature is ideal for a corner of the garden, open to the south or west, which needs to be given additional interest. It is surprising how many fine plants can be grown in this way in even a relatively small area. The low stone walls of the bed are easy to build, and with adequate drainage and skilful planting one can have a feature which gives pleasure out of all proportion to its size.

Dry Walls and Steps

Dry walls are useful for separating one part of the garden from another or for use as retaining walls. They need to be carefully constructed, without cement between the layers of stone. It is important, too, that they should have a slight backward slope to provide better support. Soil should be packed solidly behind the wall as it is built and construction will be easier if layers of soil are put between each row of stones.

As the stones which are used will be irregular in shape there will usually be spaces left between them in which alpines can be planted. Aubrietas, alyssums, houseleeks, saxifrages and erinus look delightful planted in the face of the wall.

Alpines can also be grown in steps which connect one part of the garden with another. Campanulas, geraniums (cranesbills), sedums, thymes and the wall plants mentioned above are suitable. Holes can be left for plants when the steps are built but if this was overlooked it is not difficult to make holes with a hammer and cold chisel large enough for the plants.

Troughs and Sink Gardens

If you are building a rock garden, but are short on space, rock garden plants grown in troughs, sinks and other containers can be a tremendous source of rock landscaping interest. They look particularly effective on paved areas but can, of course, be successfully incorporated into the designs of many gardens.

Drainage is extremely important and there must always be a drainage hole in the container, covered with crocks, towards which excess water can gravitate freely. When deciding on the compost to use it will be necessary to consider whether lime-hating plants are to be grown and to make the necessary adjustments. The compost should have a depth of at least 4in. with 1/2 in. space at the top for watering. If rocks are to be added position these before the sink is filled and work the soil in around them. Only a few should be used. Pack the garden soil in firmly and make sure that the sides and corners are firm, otherwise water may go straight down the sides instead of into the compost.

A dressing of stone chippings around the plants gives a good finish and deters weeds, but with lime-hating plants be careful not to use limestone chippings.

Some suitable rock garden plants for trough gardens are Androsace sarmentosa; Armeria caespitosa; the campanulas arvatica and cochlearifolia (syn. C. pusilla); Dianthus alpinus; Erinus alpinus; Phlox douglasii and its varieties; Kabschia saxifrages; and the small, compact, Sempervivum arachnoideum. Salix arbuscula, a very small willow which grows to about 9in. tall, and the very slow-growing and popular conifer Juniperus communis compressa (the Noah’s Ark Juniper), are useful for such plantings.

Once planted, a sink garden requires little attention other than hand-weeding occasionally and watering in dry weather. If the container is large enough, a few small bulbous plants, such as miniature narcissi and the smallest crocuses, may also be planted.

Propagation in the Rock Garden

Plants, such as many of the alpines available today, can be propagated quite simply either by lifting and dividing the plants or by detaching rooted offsets. Cuttings of others root readily if small pieces are detached and dibbled into pans of sandy compost. After they have been watered a pane of glass is placed over the pan and it is put either in a cold frame or in a shady place outdoors until the cuttings have rooted. The condensation must be wiped from the glass every day, and when the cuttings have rooted pot them separately into 3 inch pots using a compost containing coarse sand to ensure good drainage.

Routine Tasks When Building a Rock Garden

It is worth going over rock garden plants quite frequently to cut off dead flower heads, and autumn leaves which are blown by the wind into crevices should be removed regularly for they get wet and soggy and may kill the plants they are covering.

Some delicate rock garden plants such as lewisias and those with hairy leaves, such as the well-known Edelweiss, survive cold damp winters better if they are protected with a pane of glass. The glass can be supported over the plants on four short sticks and be kept in place with a stone. Alternatively, a cloche can be placed over the plants.