A small rock garden doesn't have to appear like a landscape afterthought. Follow some loose rules regarding what to use and how to pull everything together, from plant type and size to textures and extras, for a successful finish.
It's OK to Space Out
To differentiate a small rock garden from a pile of rocks, leave at least a few inches between the rocks and plants. Tuck an outdoor trinket or two into the design, and fill dead space with gravel or sand for a Zen effect.
Even small rock gardens tend to have a cold, gray vibe, requiring softness and color for warmth and balance. Combat visual coolness by including white and bright flowering plants that thrive amid rocks, such as pansies (Viola x wittrockiana), thriving in U.S. Department of Agriculture zones 8 through 10; and textural greenery, such as moss rose (Portulaca grandiflora), which is hardy in all USDA zones, for instance; woolly thyme (Thymus pseudolanuginosus), which grows in USDA zones 2 to 9; or any appropriate spongy, nubby or fuzzy succulent that thrives in your area.
Sizing Up Scale
Just because you're working with minimal square feet doesn't mean you have to select small plants, but be reasonable regarding scale. Opt for a variety of plant sizes, from ground cover or rock-creeping plants to modest-sized plants with large or showy gemlike flowers, such as dwarf daffodils (Narcissus minimus), which are cold hardy in USDA zones 4 to 8, to shrubs that grow several inches tall rather than multiple feet high. Give low-growing or insignificant plants more presence by potting them and then setting their pots on rocks or other upturned pots.
Rock to Plant Size
Gauge the garden's rock-to-plant sizes, watching that one doesn't dwarf the other. Place smallish plants, such as pansies in front of slightly larger or similar-sized rocks as natural backdrops. Varied rock sizes have a more natural effect, as long as they're in the same geological family, such as a grouping of granite or river rocks -- normally; in a compact rock garden, however, assorted rock colors and types can have a more attention-grabbing effect, especially if you're focusing more on the boulders, stones, pebbles and gravel, and less on the foliage for a low-maintenance setting.
Use Common Senses
A modest rock garden becomes a focal point when you add something that moves or makes sound. Again, don't go overboard with trinkets; a single windsock or simple chime on a garden stake, or a scale-appropriate fountain with water gurgling from a clay pot, catches the eye without appearing cheesy. Appease the nose with herbs, such as oregano (Origanum vulgare) or dwarf common sage (_Salvia officinalis '_Minimus'), both hardy down to USDA zone 4, or other pleasantly scented varieties suitable for your area -- plant them in easy reach for quick snipping to toss in a soup or salad.
Give your little rock garden more presence by positioning a compact bench or slim lawn chair next to it -- bulky outdoor furniture can overshadow a humble floral focal point. Tie into the rockery theme with a stepping-stone side table. Complete the seating arrangement with colorful cushions and a throw blanket, all preferably in hues that mirror dominant flower colors nearby.
For more information on choosing suitable rocks for your rock garden, see Sizes and Types of Rocks for Rock Gardens.