A Garden Set in Stone

Grasses, especially, soften a landscape anchored in stone. From the tall Miscan­thus sinensis to the short blue fescue (Festuca glauca), both plumes and foliage flow through the garden.

Stone has been the building material of choice since humans first stacked stones on top of each other to make a rudimentary shelter. Used properly, stone brings people in touch with nature, creates a sense of timelessness, and becomes an integral part of a garden. So stone was the natural choice for a native-plant enthusiast’s garden in northern California.

Our client purchased this property for its spectacular views of San Francisco and the bay, for the high-ceilinged rooms that open to the view, and for the stand of mature California live oaks (Quercus agrifolia) on the property. The structured, Modernist landscape installed around 1958 included concrete terraces linked by broad steps and wooden retaining walls painted black. It paid homage to the design of the house but did little to relate the house to the woodland environment.

Our design called for a simplification of the existing landscape. There would be fewer terraces, and stone walls and flagstone paving would replace the retaining walls and broad paths. The stone terraces where the oaks could be enjoyed would be linked with curving flagstone steps leading past boulder outcrops, a pond, and through a sequence of gardens.

Match your paving to your house’s style

More than any other hardscaping element, paving determines the character of your outdoor spaces, and it makes sense to match the paving to the style of your house. For example, if you own a Craftsman-style house, you might choose an irregular pattern of square and rectangular flagstones laid in sand. A Georgian-style house, on the other hand, calls for a more formal, rectilinear pattern.

For this garden, we wanted stone that resembled the native stone of the area. We settled on Shenandoah flagstone for the paving, Kennesaw dry-stack for the walls, and Sonoma fieldstone for the boulders. Though they come from different parts of the country, their character and color are similar, and they look as if they belong in this garden.

More important, the character of each type of stone expresses its purpose. The flagstone is smooth, broad, and flat, and “says” walking surface. The boulders are rounded but sometimes craggy and speak directly to the natural environment of the Bay area. The Kennesaw dry-stack stone is blocky and angular in character—a form that suggests they should be stacked in a wall.

Steps act as a transition between spaces

Flagstone steps are mortared for safety. The adjacent stone retaining wall, however, is dry-laid for a natural look.

As a rule of thumb, steps should match the paving to create flow between levels, as they do in this project. The exception is where you want to change from a more formal paving to a less formal one. In this case, steps can act as the transition, and you have to decide which paving they should match, or whether they should be entirely different.

Stone steps should be set on a sound concrete base, as they were in this garden, unless they are large slabs that can safely be set directly into the ground without fear of settling or movement. In this garden, we curved the runs of steps between the different levels to give the garden an organic flow. 

The flagstone steps, which are mortared to a concrete slab for long-term stability, measure 412 to 5 feet wide. The wide expanse of steps invites people to leave the terrace and explore the garden. Farther away from the house, where the emphasis is on close communion with the plants, the stepping-stone path measures only about 18 inches wide. This slows the visitor and encourages a closer look at the plants.

Select stone based on how a space is used

How a space is used dictates your choice of stone. Flat stones with mortared joints are preferable for entries, high-traffic areas, and places with outdoor furniture. Irregular, dry-laid stones are ideal for garden paths and casual areas. In either case, make sure the stone is not too rough or uneven, which could present a tripping hazard, and not so smooth as to be slippery when wet.

Also consider color, porosity, and density when choosing stone. A light-colored stone may brighten a dark area, but could also create glare in a sunny area. Porous stones can absorb too much water and may have to be sealed. A soft, thin stone should be mortared and laid on a concrete base to keep it from cracking.

In this client’s garden, the terrace under the deck, adjacent to the pond, is one of the most used outdoor spaces. It made sense to set the flagstone on a concrete slab, with mortared joints, then transition to flagstones laid on sand, with planted joints, around the pond. Further into the garden, the areas become more rustic and the flagstone again is laid on sand, with irrigation and plantings positioned in the joints.

Small boulders help mark the transition from terrace to pond and give visiting birds a place to perch.

Dry-laid walls look more rustic

In a natural setting, such as this garden, where a rustic aesthetic is desired, dry-laid retaining walls are most appropriate. The stones are simply stacked without mortar, usually battered back at a slight angle into the hill to better resist gravity.

One of the beauties of dry-laid walls is that they do not require a drainage system behind them, as water can weep through the joints between the stones. They can also flex and move in expansive soil conditions, without the cracking that can occur in mortared walls. Dry-laid walls should not exceed about 3 feet in height; beyond that, they can become unstable.

If you need something taller, or you are working in a more formal setting, stone walls can be built on concrete footings with mortar between the stones. Where desired, mortar joints can be kept thin and recessed an inch or two from the face of the wall to give the appearance of a dry-laid wall. Mortared stone walls may also have height limitations, require a rebar support system, or need drains and weep holes. Often, they require review by a structural engineer (particularly on the West Coast, where earthquake safety must be considered).

Stone can also be veneered over concrete block or a masonry wall. This might be necessary where structural concerns require a very strong wall. When veneering a wall, pay particular attention to the corners and try to avoid showing any thin edges of stone that will give a less-than-substantial feel to the wall.

When used throughout a garden, stone can become a primary unifying element. In this project, we used different types of stones, but the variety was limited to three, and these blended with each other in such a way that they all seem as one with their environment.