Walls that rock

Rock walls look better than ever, as gardeners around the West give a fresh spin to a landscape classic. One reason for their popularity is that they work in so many styles of gardens: They can look charmingly rustic, or as fresh and contemporary as the wall shown above, designed by Topher Delaney. “In gardens, stone walls tell a geologic story,” says Delaney, who likes the sense of history and permanence they bring to the landscape. Unlike wood, stone is weather-resistant and requires little or no maintenance. If built properly, a rock wall will last nearly an eternity.

Some rock walls are freestanding, but often they’re used to hold back a slope. Dry-stacked stone walls are held together by friction and gravity rather than mortar. Not only is this informal style perfect for casual Western gardens, it’s practical as well: Water draining off the slope can seep through the cracks, instead of causing pressure on the wall.

When picking out stones, choose a regional variety―moss rock in the mountains, sandstone in the desert, Sierra granite in Northern California, for instance―and coordinate it with the architectural style of your house and garden. Rocks can be flat or chunky, irregular or uniform. Use the walls shown on these pages to guide your design. Stone wall basics

Should you build a rock wall yourself? You can build low walls, but anything taller than 2 to 3 feet is best tackled by a professional. If the wall is meant to hold back a slope, consult an engineer.

• Foundation: Use 6 to 12 inches of crushed rock for short walls (1 to 3 feet high); concrete should be used for tall or heavy walls. Embed the footing, as well as the first layer of rock, in the soil.

• Height: In most cases, the slope will determine the wall’s height. For steep slopes, build several walls to form terraces (as shown on page 56, lower left). If you plan to use the wall for seating, build it about 18 inches high.

• Placement: For stability, place widest rocks at the bottom of the wall. Overlap, or stagger, rock edges as you build, and angle the wall back toward the slope 10° (about 1/8 to ¼ inch back from the preceding row, depending on site). Choose pieces that fit like a puzzle and set each one firmly in place. Use small stones to level large ones and to fill in gaps.

• Drainage: Pack soil firmly behind each layer of rock. If the slope seeps water, place a 3- to 4-inch-thick layer of crushed rock directly behind the wall.

• Price: Stone costs vary widely. Fieldstone costs about $125 per ton; sandstone or strip flagstone about $260 per ton; imported granite and basalt up to $500 per ton.