Garden renovation projects might include mounds to add visual interest in an otherwise flat terrain, and also to provide drainage and other benefits of raised beds. A particular form of the garden mound is the rock garden, based on a natural or simulated outcrop of rocks.
An outcrop could occur in a flat area, but are most common—and look most realistic when created—on a slope, where erosion over time would have exposed the underling rock formation. If your property includes an area that has a slope of ten degrees or more, and full exposure to the sun, you have a good site for a rock garden. Never mind if it lacks rocks: they can be trucked in from a stone yard.
Lacking a sloped area, the gardener could develop a rock garden on a mound, and should not be reluctant to do so, but should avoid the look of “a dog’s grave,” which results when an isolated bump is placed in a lawn. A mounded rock garden will have a naturalistic appearance when is has substantial size appropriate to the setting, and a backdrop of shrubs, trees, wall or hills.
Another contributor to a natural look is a scree boundary. The base of a natural rock outcrop often will have a loose accumulation of smaller stones and rock chips, called “scree.” So, where sufficient space is available, include a scree bed about two feet wide between the rock garden and the adjacent lawn or pathway. The scree bed should have a foundation of about eight inches of scree compost (1 part topsoil, 1 part compost, 3 parts gravel). An edging would help to contain the stones.
Acquiring and placing rocks will be the most expensive, strenuous and aesthetically challenging part of the project. Here are recommended guidelines:
- Use one kind of stone, preferably one that occurs naturally in the area. Traditionally, rock gardens use limestone or sandstone, but in the Monterey Bay area Sonoma fieldstone, an igneous rock (basalt or rhyolite), is widely available and popular.
- Commit to the project. Include boulders (stones too large for one person to move) even though they can be difficult to place in desired positions.
- Contract with the stone yard deliver materials to as close as possible to their eventual location.
- Position stones for a natural appearance: larger stones will be uphill of smaller stones; some stones might be close to other stones.
- Bury stones one-third to one-half of their vertical dimension. Stones rarely are found atop the soil.
A rock garden is just one use of stones in garden design. Stones are also used for walls, borders of beds, walkways or patios. All such uses can be attractive in the garden, partly because of the contrast between the surfaces of stones and plants. Recognize, however, the differences between naturalistic rock gardens and these other uses, in which stones are used as building materials.
20 Fabulous Rock Garden Design Ideas —from Decoist.com. These images show fine designs that demonstrate a variety of uses of rocks in the landscape. Not all designs could be called naturalistic.
Rock Garden Ideas — 112 images of rock gardens, ranging from naturalistic designs to “whimsical” ideas. Test yourself on whether these designs follow or violate the five design guidelines listed in this article.
Alpine Garden Society – This society is based in the British Isles, where rock gardens first became popular. Gardeners in the United States have developed many rock gardens, but not with the enthusiastic commitment evident in England.
The Rock Garden – Very good how-to article by Alan Grainger, with sufficient information to guide a novice project. Visit the website, The Alpine Garden for many related garden and plant photos, book reviews and other resources.
Betty Ford Alpine Gardens A large and varied place, designed for visits (not so much for web browsing). This could be the most highly developed public rock garden in the United States.
How to Build Rock Gardens From About.com – This website illustrates a “rockery,” a garden design that is based on rocks, but which does not pretend to a natural look. This might also be called a “dog’s grave.”