NOW THAT perennials have taken root in Southern California gardens, can rock gardening be far behind? In England, one style traditionally follows the other. It's as though perennials whet the gardener's appetite for unusual plants that rock gardening ultimately satisfies.
Already there are signs. In Los Angeles, several brand-new rock gardens now exist; practically none did in past years. A new chapter of the American Rock Garden Society has been formed; though it can boast only 50 members at the moment, the Southwest Chapter does manage to publish a newsletter.
In England, rock gardening is considered to be the highest form of gardening, and it represents, perhaps, the activity's most curious bent. One does not, of course, grow rocks, but rather plants that are associated with rocks and rocky soil. Enthusiasts consider the small, rare, rock-garden plants to be the jewels of the plant kingdom. Some people think this evaluation is odd, because often you can notice these tiny plants only if you're on your hands and knees. Someone on a quick garden tour could miss them altogether. Their flowers, however, are quite notable; they are either immense in comparison to the plant itself, or they are intensely colored.
The tenants of the original rock gardens were strictly alpine plants, inhabitants of mountaintops that have learned to hug the ground to protect themselves from winter blizzards and the summer's constant wind. True alpine plants are lean as well as low and grow in a gritty soil that at best is one step removed from solid rock. However, rock gardens now include just about any plant that is gem-like, including not only woodland plants that grow in the richest soils but also bog plants that grow in the dampest. The menu has even expanded to embrace many Mediterranean plants that grow in rocky soil at sea level. Those are the plants that offer the most hope for California gardeners. Only certain of the alpine plants can survive in our mild, dry climate and alkaline soil.
One way of fooling alpine rock-garden plants into feeling at home is to grow them in containers so that soil and watering conditions can be precisely controlled. Many English rock gardens are planted entirely in containers; "troughs," old stone sinks, are in such large demand that British magazines frequently publish articles about how to build suitable imitation troughs.
Many books have been written on the subject of rock gardening, especially in England. "The English Rock Garden" by Reginald Farrer (1918) is the classic work. Though it is mostly a compendium and rating of plants, the basics of making a rock garden are outlined in the opening chapters: "Having chosen an open aspect and conceived your plan, you must invariably excavate the soil to a foot or 15 inches below ground level. Now comes your soil: This must be a mixture that is both light and rich." Farrer suggests a mix still highly thought of: one-third loam (good garden soil), one-third leaf mold (or other organic amendment), and one-third sand. Farrer goes on to say that the depth of the soil should not be less than 2 1/2 feet nor more than 3 1/2. After excavating, you must mound up above that, to provide a suitable bed for these fussy plants. Rock gardening is not easy work.
All of this is in preparation for growing plants that are sometimes no bigger than a coat button. But it is the characteristic of most rock-garden plants, and all alpine plants, that their roots far outdistance their tops. The typical rock-garden plant is called a "cushion plant" because it makes a dense mound of foliage; below that is an extensive root system designed to plumb every crevice in search of moisture and nutrients.
And what of the rocks? Farrer warns against using "all derelict artificial rubbish, burrs, clinkers, odds and ends of Norman arches, conglomerated bricks, and such like," and instead recommends "the goods the gods provide"-- natural rock that might be found in the vicinity. Boulders are preferred, and they should be buried so that only the upper third is visible--like icebergs-- and used sparingly; the idea is to frame and set off the plants. The rocks are also handy for stepping on--so that the plants are not--and they provide a cool place underneath for roots. Many rock-garden plants, while needing to bask in the sun, want their roots cool, and few places are as cool as the underside of a rock.
For an interesting catalogue of rock-garden plants, send $2 to Siskiyou Rare Plant Nursery, 2825 Cummings Road, Medford, Ore. 97501.
For information on the Southwest Chapter of the American Rock Garden Society, write to Laura Jezik, P.O. Box 1382, Los Angeles 90053, or attend one of the Southwest Chapter's meetings. The next one is scheduled for June 2, at 7:30 p.m., at the Los Angeles County Arboretum, 301 N. Baldwin Ave., Arcadia.