The charm of rock gardens can be the small-scale plants, miniatures reminiscent of the alpine landscape. Or it can be the beauty of the rocks themselves and their placement. The term is applied, in general, to gardens where stones and boulders cover at least a third of the ground and the plants are either alpine natives or occur natural in rocky areas. You don't need to limit yourself, however, to the traditional.
Rocks and Boulders First
Large boulders dominate a garden, so use just a few, buried deeply so they look as if they belong. Surround them with smaller rocks in a similar, rounded shape, or set off by the squared edges of paving stones. Don't be afraid to use them in formal designs, where their natural contours can be a dramatic contrast to the linear and geometric lines of paths and beds..
Dry stream beds, imitations of a natural watercourse without the water, are especially effective in shady areas. You can grow small wildflowers and ferns along the edges, softening the effect of the rocks.
Finding Your Scale
If you want to create a miniature alpine landscape, consider a tiny rock garden, only a few feet wide, in a low container, perhaps a Japanese bonsai pot. Or, you could landscape the edge of a walkway, a long, narrow rectangle, as an alpine meadow, complete with inch-high mats of wildflowers and "boulders" only a foot high.
Or, with enough space, create rocky outcroppings 3 or 4 feet wide, where dwarf conifers--3 feet high--would seem perfectly sized and dwarf iris a foot tall could be grown in clumps for a meadow effect.
Playing With Texture
Whether your rock garden is large or small, vary the texture to create interest. Lance-leaved, linear plants such as iris and sisyrinchium are effective foils for delicate ferns and tiny leaved plants such as dianthus. Include a few flowers with rounded leaves or comparatively bold leaves such as heuchera and sempervivum.
Flowers Up Front
Succulents and drought-tolerant plants are often used in rock gardens, but you don't have to limit yourself to insignificant plants. Given partial shade and regular watering, you can grow primroses and many kinds of wildflowers, the smaller kinds of spring bulbs such as Scilla siberica, as well as lewisias and shooting stars (dodecantheon).
In sunny spots, use colorful groundcovers such as Lithodora and the myriad varieties of Dianthus. Experiment with the dwarf varieties of perennials now available. If a plant proves to be too large, simply move it to another part of the garden.
Natural vs. Patterned
Many rock gardens imitate natural areas, but you don't have to limit yourself to one style. You can use rocks to create swirls and geometric shapes, then plant them with informal clumps of perennials or even a single type of plant, such as heather. Plants grow and change shape, rocks don't, so create your design with stone then use plants to soften it and add color.