Many small flowers or creeping vines work well in rockeries. But you do need to find varieties of plants that do well in the climate, light conditions and soil for your specific rock garden. Luckily, some traditional rockery plants do well in most locations and some are easy to grow in all light and soil conditions. The Landscape Design Site recommends that you choose rocks with similar appearance to create a natural appearance for your rockery.
Spreading in wide clumps with small, profuse flowers of white or purple, alyssum is a traditional rockery choice because it is a perennial in most climates. The plant may grow as tall as 1 foot, but some varieties are as short as 6 inches. The flowers are fragrant and bloom from spring through summer, often lasting until the first frost. Sow alyssum directly from seeds, or root small clumps of the existing plant directly into the soil. Alyssum prefers cool weather but will do well in warmer climates with ample water.
Potentilla is a small, perennial shrub that produces profuse small, bright yellow blossoms covering the 4-foot plant all summer and into the fall. It is easy to grow in all types of soil and prefers full sun, though it will do well in partially sunny areas in warmer climates. Prune the plants if you need or want a smaller, more compact shape for the rockery. The gray-green potentilla leaves provide a contrast with other plants.
Recommended by the "Sunset Western Garden Book" as one of the easiest rock garden plants for all climate zones, sedum acre, or goldmoss sedum, is an evergreen plant with tiny, light green leaves and clusters of yellow flowers that bloom in mid or late spring. It grows from 2 to 5 inches tall and has trailing stems, making it easy to transplant by digging up the stems and planting them directly in the soil. The "Sunset" editors caution that while the hardiness of sedum is a benefit, it can also become invasive if not kept in check by regular pruning.
The "Sunset" editors cite veronica as a perennial that grows well in all climate zones and a traditional plant for a rock garden. Also called speedwell, the plants ranges in height from 4 inches to 2 ½ feet. Flowers in shades of blue, pink and white grow in erect spikes on leafy stems ranging from 10 to 18 inches high. Veronica does best in a sunny location and looks most effective when three or more plants are massed together.