In the garden, one thing always seems to lead to another.

I began by thinning one plant that had begun to crowd a bed in my garden. The plant is the Rain Lily (Zephyranthes candida), a low-growing bulb in the Amaryllis family, native to South America. It has grassy foliage, evergreen in the Monterey Bay area, and six-petal blossoms, white with a pink wash. (Pink blossoms are more common in the genus.)

After a few seasons in the ground, the Rain Lily generates many small bulbs and spreads happily. My original one-gallon clump expanded to fill nearly half of a semi-circular bed about thirty-feet in diameter.

I gathered hundreds of bulbs to share on June 23rd through the Garden Exchange at The Garden Faire (thegardenfaire.org).

That project created open space in that prominent front yard bed, and the opportunity to rethink its design. A rock garden seemed an obvious choice: the bed is already mounded and has a few largish boulders.

My preliminary inquiries into rock garden design revealed that this bed doesn’t qualify as a rock garden, but is instead a “rockery.” A rock garden has particular soil, rocks, and plants; a rockery is simply any planting bed with decorative rocks.

Serious rock gardeners study instances in which plants grow in a rocky environment. This occurs typically in a mountainous region, which will have high elevation, rocky ledges on sloping sites, rock outcroppings on more level land, and crevices, which are narrow, soil-filled spaces between rocks. The soil in such regions typically will be poor in nutrients and fast to drain. The climate usually will be windy and marked by much sun exposure.

The plants in a natural rock garden will have evolved to survive in those relatively hard conditions. The classic rock garden plants are called “alpines,” meaning plants that grow in The Alps, one of the great mountain range systems of Europe. These plants could be herbaceous or woody, and grow up to about one foot high.

Another category of rock garden plants includes small rock (“saxatile”) plants, which grow in rocky sites at lower elevations. These plants are easier than alpines to grow in most residential gardens because the gardener doesn’t need to recreate the uncommon conditions of a mountainous environment.

A popular feature for rock gardens is the scree bed, an area of loose rocks and stones that might occur at the bottom of a slope, perhaps deposited there by a landslide. A larger rock garden might have a sand bed, an acid heath bed, an “alpine meadow, or a boggy area beside a pond or stream.

A rock garden could succeed in a small setting as well, making this interesting naturalistic design concept adaptable for placement in gardens of all sizes.

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A small rock garden could be created in a container. An appropriate container would be a hypertufa trough, which you can build yourself. Here are instructions from Fine Gardening magazine.

If you have larger project in mind, take the time to research the basic concepts, to be sure you are on the right track and won’t end up with a rockery instead of a rock garden. There are good books on the subject. Here are three that are available on Amazon.com:

Rock Garden Design and Construction, by North American Rock Garden Society (2003)

The Serious Gardener: Rock Gardens (New York Botanical Gardens), by Ann Halpin and Robert Bartomonei (1997)

The Rock Garden Plant Primer: Easy, Small Plants for Containers, Patios, and the Open Garden, by C. Gray-Wilson (2009)