Using Rock in the Landscape

By G. Owen Yost

There is nothing as timeless and dramatic in a landscape as rock. Think Stonehenge, castles and cathedrals. Picture dry-stacked rock walls along a country lane. Rock can provide that "been-there-forever" patina to any yard.

Your first choice for almost any project is rock that's found locally. In my part of North Texas, that often means limestone with some reddish highlights from the iron in the soil here. Local rock not only blends comfortably with the surroundings, but it's almost always less expensive, since transportation is one of the biggest factors in the price.

Imported or artificially colored rock may look exotic, but rarely blends visually with the native plants and soil of Texas. In your area, rock is probably available in a wide range of subtle hues, from blue-gray to cream to iron-ore red. Don't forget that rock weathers with exposure to the elements, changing the color over time. Softer stones, such as limestone, weather faster and more dramatically than harder stones such as granite.

Flagstone is rock that is used as a walking surface for pathways, patios and stepping stones. The rocks need not be perfectly flat, but bear in mind that rough stones may create a tripping hazard, and some types of stones may be slippery when wet. Sandstone has a notably nonslip surface. Larger stepping-stones create a more stable and attractive path. Rocks can be laid directly on bare soil if they're at least four inches thick. Thinner rocks break more easily and should be laid in a bed of crushed gravel or sand (with cement added for stability).

Another popular landscaping rock is gravel--usually with a diameter of one-half inch or less. Gravel can be all one color or even artificially colored, but the most attractive types are multicolored. If the gravel is intended for a walking surface, the individual rocks should have rounded edges (usually the product of centuries of water erosion). Newly crushed gravel has sharp edges and is better used for backfill or in other unseen locations.

Gravel is usually sold by the ton or cubic yard. A cubic yard provides about 80 square feet of area at a four-inch depth. For a two-foot-wide path, that's 40 feet long. This is a good rule of thumb, since many people use two-by-fours to form up their pathways and patios. A ton of gravel is about three-quarters of a cubic yard.

The best selection of materials and the most knowledgeable people to advise you are usually found where contractors and landscape architects shop--rock yards or quarries, not home improvement centers. Look under "rock-natural," "rock," "building materials" or "landscape equipment" in the phone book.

Boulders are a dramatic addition to any landscape. They should be somewhat weathered (and without sharp edges) for an aged look--some may even have moss growing on them. If you're planning to have a grouping of decorative boulders, one should be significantly larger and more interesting than the others. Bury the bottom third in the dirt, as if the whole group were emerging from the ground.

Getting the rocks home is a weighty problem. Some sources will deliver for a nominal fee; others for free if they will be doing the construction. Usually, the rocks are too heavy for the trunk of your car or even a small pick-up truck. Rock weighs anywhere from 150 to 220 pounds per cubic foot, depending on density. Although most sources can easily load your truck, unloading at home can be difficult and dangerous. Even slight movement of a large rock can break a finger or smash a foot. The unloading site should be very close to where the rocks will be used.

Remember that when using rock there is one firm, overall rule--make every effort to build it right the first time, because it will be hard to rebuild.

Owen Yost is an area landscape architect specializing in designing low-maintenance landscapes while incorporating native plants with hardscape. He is a member of the American Society of Landscape Architects, Keep Denton Beautiful and the Native Plant Society of Texas. His Denton office is at 4516 Coyote Point; call 940-382-2099 or 940-383-9655 or e-mail him at Yost87@charter.net