The Golden State: Where & How to Live, Secure, Visit, Enjoy and Thrive in California
American Rock Gardens
From habit of growth there are several types of rock plants; and their position is decided largely by their habit. Most distinct are the tufted plants, forming rosettes of foliage with short flower stalks above. These are for cliffs and tiny crevices, usually at the highest levels, and are the alpine vegetation. Such are Alpine Thrift (Statice montana), Tufted Saxifrage (*Saxijraga caespitosa), Alpine Poppy (Papaver alpinum), Banded Pink (Dianthus zonatus), and Smooth Alumroot (*Heuchera glabra).
Next there are dwarf erect plants of one foot in stature or less, small relatives of border plants. These are for the large flat areas and tops of ledges, where they are above the creeping sorts. These give height to the plantings. Try Rock Aster (*Aster alpinus), Alpine Columbine (Aquile- gia alpina), Yellow Pink (Dianthus knappii), Harebell (*Campanula rotundifolia), and Mountain Phlox (*Phlox ovata).
The drooping plants prefer to hang down over a rock face, growing in long streamers. These are best in the steep slopes near the top, though they smother any plants below them. On flat areas they soon crowd out smaller and less vigorous sorts. These are the plants that give foliage bulk to the rock garden and may be depended on to give the planting an effect of luxuriance, covering all blank spaces and even making the stones disappear in a sea of foliage. Goldentuft (Alyssum saxatile), Snow-in-Summer (Cerastium tomentosum), Evergreen Candytuft (Iberis setnpervirens), Moss Phlox (*Phlox subulata), and Carpathian Bellflower (Campanula carpatica) are examples of drooping plants of very vigorous growth.
The creeping sorts form close mats on the ground, rooting at the joints and covering the soil completely to a depth of a few inches. These fill in all tiny cracks in flat or sloping places, reaching across the stones after all the soil has been covered. For carpeting in the walks these are very useful, but this may not be sufficient domain and they clamber into the pockets and overwhelm the rare tufted kinds. Common Speedwell (*Veronica officinalis), Maiden Pink (Dianthus deltoides), Creeping Phlox (*Phlox stolonifera), Mother-of-thyme (Tkymus serpyllum) and Stringy Stonecrop (Sedum sarmentosum) are very vigorous and crowding creepers.
Through such matted plants as these the little bulbs, as Snowdrop and Squills, (see List B, Chapter VI) will push their way and bloom in spring against a background of foliage; and when they dry away, there will be no patches of bare dirt above them.
All kinds of plants may be found in a modern rock garden, but some of them are hardly suitable. It might be well to put certain limitations upon what may be called a rock plant. Except in very large rock plantings or as special accent, a rock plant should not be more than a foot in height (or 30 cm) on the average. This restriction in height is necessary to keep the plants in scale with the scenery.
