Rock gardens present the gardener with a challenging growing environment. It is a solution to use on an awkward slope where mowing or other forms of maintenance are difficult to perform. A rock garden is composed of rocks and good-draining soil built to appear as a natural rocky outcrop. Use very large stones to create the backbone of your garden, along with a collection of smaller rocks to form planting areas. In a rock garden, plants are arranged to look natural among the rocks.
Tall plants can hide the rocks in your rock garden, so you want low-growing plants. Dwarf juniper (Juniperus procumbres "Nana") is an evergreen bush that grows 12 inches tall and 3 to 4 feet wide. The creeping juniper (Juniperus horizontalis) does not grow taller than 6 inches but will cover an area 6 feet wide. Creeping cotoneaster (Cotoneaster adpressus) grows 1 to 1 1/2 feet tall and spreads 4 to 6 feet wide. Dwarf azalea (Rhododendron atlanticum) is the tallest specimen at 3 to 6 feet tall and 3 to 6 feet wide. A good groundcover is mountain pinks (Phlox subulata), which grows 4 to 6 inches tall and spreads 2 feet wide.
Low-growing and creeping perennials are used to fill in the gaps between the larger plants. Try rock cress (Arabis), stemless trumpet gentian (Gentiana clusii), pasque flower (Pulsatilla halleri), Chilean wood sorrel (Oxalis andenophylla), moss phlox (Phlox subulata), meadow saxifrage (Saxifrage granulata), stonecrop (Sedum spathulifolium "Purpureum") and yarrow (Achillea) to make a colorful statement. Schorbuser Blut Dragon's Blood (Sedum spurium "Schorbuser Blut"), Goldmoss sedum (Sedum acre), hens and chicks (Sempervivum tectorum), ice plant (Delosperma cooperi), Matrona stonecrop (Sedum telephium 'Matrona') and varigated stonecrop (Sedum kamtschaticum) give you other low-growing options. Dig the holes between the rocks big enough to hold the entire root ball. Firm the plants in, and sprinkle 1 inch of coarse sand around the plants to help hold the plant in place.
Rock Loving Annuals
When annuals are used in a rock garden, they give the gardener the option to change flowers and plants each year. Some annuals to try are African daisy (Gazania species), baby's breath (Gypsophila elegans), annual phlox (Phlox drummondii), California poppy (Eschscholzia californica), cape daisy (Dimorphotheca qurantiaca), creeping zinnia (Sanvitalia procumbens), cup-flower (Nierembergia) and edging lobelia (Lobelia erinus). More colorful options include forget-me-not (Myosotis sylvatica), French marigold (Tagetes patula), rose moss portulaca (Portulaca grandiflora), sand verbena (Abronia umbellata), Swan River daisy (Brachycome), sweet alyssum (Lobularia maritima), moss verbena (Verbena hybrida) and wishbone flower (Torenia fournieri). Just sow the annual seeds in the pockets of soil between the rocks.