Traditionally, rock gardens were meant to show off plants that naturally grow in rocky landscapes. Today, rocks are used as a decorative tool in many gardens to show off or divide planting areas. They are often built on a hill or slope. Perennial plants (plants that will return to bloom the next spring) used in rock gardens are those that can thrive in rocky soil, and they are usually compact or trailing varieties.
The mountain alyssum (Alyssum montanum) is a short alyssum that reaches a maximum height of 10 inches in a neat, mound form. The plant thrives on dry, rocky soil and prefers full sun. Mountain alyssum blooms from April to May and has masses of yellow flowers, which show up brightly against the silvery-gray foliage.
Biokovo (sometimes called cranesbill) is a trailing groundcover. The plant features long-lasting, white or pink flowers from May through July and green foliage that turns brilliantly red in the fall. This short, dense perennial has an average height of between 4-10 inches and will grow in full sun or partial shade.
Candytuft (Iberis sempervirens) is a popular trailing plant that is frequently seen cascading over retaining walls or the edges of containers. This plant has evergreen foliage and blooms profusely all summer long with bright white flowers. Candytuft can reach a maximum height of 12 inches and prefers full sun or dappled shade.
White Evening Primrose
Primroses in general are hardy perennials. The white evening primrose (Oenothera speciosa) adds a magical touch to any rock garden with its day-blooming flowers of pink or white that fold up at night. This plant will bloom from June until early fall with proper care. The white evening primrose prefers full sun during the day and well-drained soil. Each flower can grow up to 12 inches tall, and they make a dramatic statement when planted in bunches.
Dragon's Blood Sedum
Dragon's blood (Sedum spurium) is a very hardy, fast-spreading ground cover that grows well in cool, shady areas of a rock garden. The plant prefers moist soil and has succulent leaves. This sedum is terrific as a fall-blooming flower in a rock garden. It blooms in early fall with masses of short, bright-red flowers. In addition, the green leaves turn burgundy in the fall. Dragon's blood sedum can attain a maximum height of four inches but can spread indefinitely.