9 Tips for Designing & Building a Rock Garden

What to Know, What to Grow

Rock garden in landscaping: image.
A lot goes into picking suitable plants to grow in a rock garden. Mark Turner/ The Image Bank/Getty Images

On the face of it, rock garden design may seem simple enough, but there is more to it than first meets the eye. A rock garden can be loosely defined as any garden in which genuine mineral stone is used in a natural manner as an essential visible component of the garden design. The stone is meant to be seen and appreciated in the same way that the plants are, not merely used as a hardscape building material.

But a good rock garden is by no means achieved by merely putting stones, soil, and plants together. Each component must be carefully selected, and then just as carefully arranged in a manner that makes the garden seem natural to the style you choose. In most cases, the garden should strive to emulate the natural geology and topography of a specific region. Japanese rock gardens, for example, are usually styled to emulate the look of mountainous regions of Japan, using plants indigenous to that region.

Here are nine tips for creating a rock garden that will be easy to maintain, aesthetically attractive, and natural in style.

Choose the Right Rocks

In most cases, it is best to choose indigenous rock for your rock garden—the type of rock that is naturally found in your region. Using stone commonly found in your area will make your garden seem like a natural feature of the landscape. Most regions have certain types of rocks that are most common. In much of Maine, for example, dark granite outcroppings can be seen in the roadcuts and ravines, and this kind of stone in a rock garden will seem quite natural. In the upper Mississippi River valley, the layered limestone of the bluff country is a natural choice for a rock garden. In other regions of the upper Midwest, it is the rounded boulders created by glacial action that makes for the most natural-looking rock garden.

In addition to making your rock garden look more natural, there is another huge advantage to using indigenous stone. Rock is a very heavy building material and shipping costs are very high. Building a rock garden in Illinois using Maine granite will be an expensive proposition, compared to building it with limestone rock harvested from river bluff just a few miles away.

That's not to say that you can't build a rock garden with non-native stone. If you live in Kansas and have your heart set on a Zen garden or alpine garden, for example, there's nothing wrong with using California coastal granite or Rocky Mountain schist in your construction.

Because a weathered look is generally preferable in a rock garden, porous, softer rock is usually a better choice than harder rock. Harder rocks take longer to acquire the weathered look that you are striving for in a rock garden because they are less receptive to the growth of mosses and lichens. Promoting the weathering of your rocks will give the rock garden a natural look; weathered stone looks as if it's always been there.

Also, stick to rocks that look the same in texture, color, and form. If you use rocks of similar appearance throughout your rock garden, it will have a more natural look.

Find Affordable Sources

A large rock garden can be an expensive proposition, so it makes sense to look for affordable stone. If you approach the project in a mood of economy, there is no reason why it should cost you an arm and a leg.

At first glance, a local quarry, stone yard, or large landscaping company is the logical place to start your search. Landscaping stone is usually sold by the ton, with delivery charges added on, so you can quickly figure out how much your rock garden will cost. You will likely find that indigenous stone common to your region is the most affordable. If you have the use of a pickup truck, it can save you hundreds of dollars in delivery costs.

But before spending money on stone, also consider the possibility of free rock. Local home-building sites or other excavations may unearth a lot of rock, which may be free for the taking. If you live near agricultural areas, farmers who routinely plow up stones will often be delighted to have someone take it away for free. In some areas, roadcuts through rocky hillsides may shed rock due to frost-thaw cycles, and local authorities may allow you to haul this rock away for free. Always ask, though, before you begin gathering rocks from along hillsides or from public lands.

Consider the Style

Rock garden design can take many forms. Today, the goal is often to create a garden that resembles a native landscape, using plants similar to those found in rocky areas of the local landscape, but you can also create a variety of themed rock gardens. For example, you will hear the terms "alpine gardens" and "Japanese Zen gardens" used in connection with rock gardens.

Japanese Zen rock gardens provide a place for quiet reflection and contemplation. Their approach tends to be minimalist, making as strong a statement as one can with the fewest components. In a typical Japanese Zen rock garden, for instance, a few choice, carefully placed rocks might form a focal point, set off by a large expanse of tiny rocks or sand that serves as a mulch. The mulch can be raked to form an intricate yet simple pattern. Compared to the Western approach, the plant material is de-emphasized—there may be a few small trees and shrubs, but few other plantings.

In the West, the interest in rock gardening began in the U.K. British travelers to the Swiss Alps were fascinated by the alpine plants that they found there and brought some back to try to grow them at home. To this day, rock gardens are sometimes referred to as alpine gardens for this reason. Although we have now expanded upon what a rock garden can be, rock gardening in the West traditionally meant the cultivation of mountain plants and other low-growing plants that can withstand the kind of winter cold to which true "alpine" plants are subjected.

Decide early whether you want one of these time-honored classic rock gardens, or instead prefer a rock garden modeled after the geology of your own area.

Use the Right Building Tools

For DIYers, building a rock garden is among the most physically challenging tasks you can undertake. A 1-foot-diameter rock can easily weigh 45 pounds or so, and a 2-foot-diameter boulder, not uncommon for a rock garden, can tip the scales at 250 pounds. There can be many thousands of pounds of stone that need to be moved and placed to build a rock garden.

Since moving rock can be dangerous for those with back problems (and can induce back problems in those formerly free of them), start out by purchasing a back brace. To move the rocks to your future rock garden, there is, of course, the option of bringing in power equipment or winches or hiring a contractor. But if you want to rough it and do the work yourself, consider the following tools:

  • A 5-to-6-foot steel bar provides better leverage than a mere crowbar.
  • A two-wheel dolly is preferable to a wheelbarrow. An upright dolly has a vertical lower platform that can usually be easily slipped under moderately large stones to move them.

And you will also need the normal array of earth-moving tools: shovels, rakes, and a wheelbarrow.

Strive for a Natural Stone Placement

How you arrange the stones in the rock garden is very important in achieving a realistic and pleasing rock garden. Taking your cue from nature, the goal is to make it appear that the stone in your rock garden is merely the exposed fraction of a massive underground formation. This is why rock gardens so often incorporate hillsides or elevation shifts—in the natural world, erosion of slopes is where rocks are most often exposed.

To achieve the look of natural rock, each stone should appear firmly grounded—the "tip of the iceberg." Each stone also should appear as if connected to its immediate neighbors, separated only by the crevices in which you will be growing the plants.

As in the natural world, stay away from constrained stone patterns and any too-even distribution, striving instead for a feel of randomness in your rock garden. Have a massive grouping of stones here, a smaller grouping there, and mulched areas in between. The arrangement is crucial to achieving the look of natural stones.

The stones in a rock garden should relate to each other as if they comprised a bedrock formation exposed either by gradual weathering or by more dramatic erosion. Consequently, the major rock faces should point in one direction throughout the rock garden. If the stones are stratified, position the rocks in each grouping so as to have the strata lines all going in the same direction, as they would in most natural stone formations.

Create an Aged Look

Rock gardens are most aesthetically pleasing if the exposed rock faces look weathered and worn. When the rock is brought in from outside the property to construct a rock garden from scratch, it can look out of place. Its "newness" can stick out like a sore thumb, especially if there are no signs of weathering. The weathered look is most readily achieved by encouraging the growth of moss or lichens on the rock faces.

Moss is fairly easy to establish on new rock. Begin by harvesting some patches of moss you find growing somewhere else—you can even use moss growing on the ground in some shady area of your own lawn. Add about 2 tablespoons of ground-up moss to 2 cups of yogurt and about 4 ounces of potter's clay. Puree the moss, yogurt, and clay together into a creamy consistency, then apply this moss mixture to the face of the rocks. As the rock moss takes hold in your rock garden, mist it to keep it moist. Within a matter of a few weeks, you will have rocks that appear as though they've been in place for decades.

Another way to create a weathered, natural look is to encourage the growth of lichens on the stones. Although lichens are often mentioned in the same breath as moss, these are entirely different forms of primitive plant growth. Lichens are compound organisms composed of two or three individual organisms existing in a symbiotic relationship. The dominant partner is a fungus supplying food by photosynthesis (often through a colony of algae). When growing on rocks or trees, lichens appear as colorful rough patches. There are more than 20,000 species of lichens, often appearing as yellow, green, gray, or white growths on stone or wood.

Lichens are important in rock gardens and xeriscaping because they are not dependent on a steady supply of water. Lichens survive alternate drying and wetting of their tissues, giving them an advantage in colonizing difficult environments. Like mosses, lichens growing on rocks give your rock gardens the desired "weathered" look.

Getting lichens started on the stones in your rock garden is a similar process to fostering moss. Fill a spray bottle with milk, then collect about 2 teaspoons of lichens from an environment that's similar to your rock garden. Most lichens prefer moist, shady conditions, but there are also some forms that grow well in sunnier locations. Grind up the lichen flakes, add them to the spray bottle, and shake gently to mix. Spray the stone surfaces with the milk solution until the liquid runs down the face. You may need to reapply this mixture once a week for several weeks until active growth starts.

Create the Proper Soil

Once the rocks have been set in place to form the foundation for your rock garden design, you should prepare the soil before planting. Building a rock garden often involves creating an artificial slope or raised elevation, so it's common to add prepared soil rather than using the garden soil already present.

Creating the right soil for your rock garden goes hand-in-hand with plant selection. If you're planning on a classic alpine rock garden with plants consistent with that theme, then fairly porous, rocky soil will be most appropriate. A rock garden with succulents and cacti, on the other hand, will require a sandy soil—maybe even a commercially prepared cactus potting mix.

In nature, most plants that grow among rocks like well-drained soil. As a general rule, then, you would want to mix sand into the soil that you are using for planting. But it is best to know the particular requirements of the plants that you will be selecting and to base your soil preparation on that. Most traditional garden plants when grown in rock gardens will do fairly well with a good-quality garden soil (black dirt) blended with peat moss, compost, or another organic amendment.

Choose the Right Plants

If you are striving for a natural native look for your rock garden, pay attention to what types of plants naturally grow in the rocky areas in your region. Arboretums and public gardens often do a good job of creating this kind a natural look, and you can use their examples as a model for your plant choices.

If you are aiming for a themed garden—such as an alpine, desert, or Zen rock garden—then choose your plants accordingly, based on examples you find attractive.

In general, we expect rock garden plants to be low-maintenance, and we forgive them for a certain degree of plainness in the trade-off. The rock garden plants used to complement the rocks should be selected largely with your climate and other practical considerations in mind—this will help keep them low-maintenance:

  • Rock gardens in warm climates call for plants different from those used in colder climates.
  • If you live at high altitudes, you might want to consider a classic alpine rock garden.
  • If you live in the desert, cacti and other succulents are a sensible choice. As a bonus, they also blend in beautifully with rocks.
  • If your climate is warm and humid, ferns can be an excellent choice, as are begonias if you desire a flowering plant.

Plant selection goes hand-in-hand with soil preparation. Pay attention to the pH preferences of your plants. An individual plant choice may prefer acidic or alkaline soil, and it's difficult to mix low pH (acid-loving) plants with high pH plants (those that prefer alkaline conditions).

Whether your rock garden is in a sunny or shady location will have a great influence on the plants you select for planting. Learn all the requirements of your plants, and avoid outliers that have unique needs unlike the other plants in the garden.

Position Plants Carefully

When it comes time to plant, strive for an arrangement that looks natural. As a model, observe a local rocky terrain with wild plants growing on it. Rather than a hodgepodge of species, you normally find sizable colonies of low-growing plants. If you like creeping phlox, for instance, but never know where to put it, your problem is now solved: a rock garden is potentially a great place to plant a large mass of creeping phlox. For dry ground, a similar mass of 'Angelina' sedum would be better.

Evenness in size or distribution looks unnatural in rock garden design. Rock gardens are usually fairly natural-looking, informal plant arrangements, not a place for formal symmetry or straight lines.