A rock garden can be a handsome addition to many a landscaping plan. Featuring artfully arranged stones and uncommon plants usually found only at high altitudes, rock gardens thrive in a variety of light conditions and require little maintenance.
Since alpine plants prefer relatively dry soil, slopes offer the best chance of success because of the superior drainage there. Choose an east-facing slope over a northern exposure, and avoid southern and western slopes; they receive too much warmth for alpine species.
A rock garden can mimic the geology of any area, but rather than importing stones from afar, a simpler approach is to imitate local surroundings. Flat, jagged hunks of sandstone may define the character of a rock garden design in one region; in another, granite boulders may predominate. In any case, emphasize large stones, and intersperse smaller ones among them.
The character of a rock garden depends as much on plant selection as on the kind of rock used. Choose from among the alpine varieties offered in the appendix or visit your local nursery for assistance.
Preparing a rock garden for planting involves a fair amount of labor. Even an incline’s superior drainage needs improving before you can set rocks into the slope (opposite), singly or as outcrops—stacks of two or more. Tips for maneuvering heavy objects appear on page 25, but don’t hesitate to contact a landscaping company to help with the largest stones.
Before excavating, note the location of underground obstacles such as electric, water, and sewer lines, or dry wells, septic tanks, and cesspools.
Anatomy of a rock garden
The most attractive rock gardens mimic a natural-appearing environment of rocks and plants in an aesthetically pleasing way without seeming studied or fussy. When designing the garden, consider each plant’s growth habits, blooming schedule, height, and light requirements. Then, place plants in the setting you have created as they might grow in the wild.
Preparing the bed
Strip the sod from the site and remove about 18 inches of soil. In the bottom of the hole, spread a 6-inch layer of rocks or broken bricks, covered by the sod, placed grass side down (left). If there was no sod, cover the rocks and bricks with smaller stones or coarse sand. Mix 2 parts of coarse sand to 1 part each of the soil from the bed, compost or peat, and crushed stone. Fill the hole to ground level with the mixture.
Setting large rocks
Arrange the rocks atop the soil mixture in the desired locations. Starting at the bottom of the slope, cut a step deep enough to accommodate at least one-third the width of the first rock. Make the back of the step lower than the front so that rainwater will run toward the slope. Place the rock into the step with the long side parallel to the slope (left). Pack soil mixture around the rock, filling any air pockets. Stand on the rock to test its stability. Repeat for each large rock.
Building a rock outcrop
Where an outcrop is desired, use one of the rocks set previously as a base. Select large stones that match the appearance of the base rock so that when finished the outcrop resembles a natural formation. Cover the base rock with an inch of soil and position another rock on top of it. Use a digging bar—a long metal tool helpful for gaining leverage, available at garden centers—to maneuver heavy specimens (right). Repeat this process to add stones to the outcrop.