Many different plants could be included in a rock garden. The usual design approach limits plant selection to low-growing varieties, but this is not a necessary constraint.

A brief study of the vegetation on a naturally occurring rocky landscape would help in designing a realistic rock garden for a residential landscape.

Some travel could be required to locate one or more good examples; this could be a pleasant weekend excursion with a clear purpose, especially if one knows where to find rocky landscapes. Ask around!

Once found, rocky landscapes might include one or more trees of various sizes, as well as shrubs and smaller plants. Clearly, proximity to rocks does not limit the size of plants.

A late July scene in the rock garden of the University of British Columbia Botanical Garden; photo by Todd Boland.

The assumption that rock garden plants should be low-growing specimens probably relates to alpine gardens, which have inspired many rock gardens. Alpine gardens feature plants that grow naturally in high-altitude, mountainous areas, which typically have large stones and much gravel, low temperatures, low moisture, and poor soil nutrition. Plants that survive under such conditions might very well be small in overall size and low growing.

Developing an authentic alpine garden, however, involves reproducing the challenging conditions in which alpine plants are found. There are alpine varieties of some familiar garden varieties, e.g., Campanula, Dianthus, Geranium, Phlox, Primula, Ranunculus, Sedum, Sisyrinchium, Thyme. If such plants were to be grown in a moderate climate, in rich soil and with ample moisture, they would respond with more lush growth and greater size than they would in a true alpine garden.

Rock gardens should not be confused with alpine gardens. In fact, rocky landscapes can and do occur in a wide range of climates, with the only common characteristic being exposed rocks. So, in planting a rock garden, the gardener should first select plants that will thrive in the local environment. The Monterey Bay area’s climate supports a wide range of choices.

The rock garden designer still might want to emphasize low growing plants to keep the vegetation in scale with the surrounding landscape and the rock garden itself, and to keep the rocks visible (they might have required a significant investment).

Another consideration is the relationship of the plants to each other. This perspective might lead to developing a plant community, i.e., a grouping of plants that grow together in nature. Other possibilities include a thematic approach, e.g., a white garden or an analogous or complementary color scheme. In our moderate local climate, the designer also might plan for year-round seasonal color, or for interesting contrasts of foliage or structure.

There are many possibilities, but the most successful and satisfying landscape plans always are based on a plan of some description, rather than a series of impulsive decisions.

More

Alpine Garden Society – Plants –This is a thoroughly amazing website, a vast treasure trove of images and information about alpine plants. At the site, click on “AGS Encyclopedia” then on either “Families,” “Genera,” Species,” or “Authors” for encyclopedic information. (I found “Genera” most useful.)

The image above came from Images/Photographic Competition/Previous Winners/AGS Photographic Competition, 2012 – Winners

The website invites—and requires—exploration to discover its many riches.

North American Rock Garden Society – Another good source of plant images and descriptions. Not as extensive as the Alpine Garden Society’s website, but helpful as an introduction to rock garden plants. At the site, click on “Plants” for the entry to lists and images.

Rock Gardens & Ground Covers A page of unorganized photos submitted to Pinterest. Interesting to scroll through, to see some very good plant pictures, some attractive designs (more or less naturalistic) and some truly bad designs (but that’s one person’s opinion).

Scottish Rock Garden Club – This website provides free access to many back issues of The International Rock Gardener, an excellent publication.

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.

More

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.”