Bulbs in the Rock Garden

Rock gardens are not merely a beautiful setting for many bulbs, but, among ever-increasing numbers of gardeners, a way of life. The North American Rock Garden Society is only one of the gardening groups devoted to the art of rock gardening. As a wider range of plants becomes better known to home gardeners, rock gardens will undoubtedly become more common in the United States.

What is a rock garden? In short, it is a sloping garden with rocks and gritty soil. To some extent it replicates the natural environment of alpine plants—plants from mountainous or rocky terrains. Many have brief but spectacular periods of spring bloom and then become dormant during the hot, dry summer.

Climates with a brief growing season followed by a long period of adverse weather foster the evolution of bulbs. Many bulbs thrive in alpine conditions. These can be planted in rock gardens as specimens or, more often, in clumps or drifts. Most rock gardens are situated for maximum sun exposure, although they usually provide some sheltered sites (behind rocks, in crevices, or on north-facing slopes, for example) for plants that require shade. Alpine plants have evolved in environments where compact growth is a survival advantage, and many are small. Some plants, including many bulbs that look and grow best in rock gardens, aren’t alpine in their origins but still thrive in rock gardens because of the quick drainage.

Rock garden soils usually contain generous proportions of sand, grit, and even gravel, together with organic material such as peat moss. In a rock garden, a gravel or grit mulch looks natural, discourages weeds, and keeps crowns and lower leaves of moisture-sensitive alpine plants from rotting. It also keeps blossoms from being splashed with mud.

Rock gardens are usually raised above the natural grade. The elevation of a rock garden not only helps drainage, but also displays the compact plants closer to eye level than flat beds do. For instance, Crocus speciosus viewed close-up reveals exquisite patterns of purple feathering.

Garden spots that aren’t strictly parts of a rock garden can meet the needs of rock garden plants and display them to great advantage. For example, crocus, grape hyacinth, oxalis, and scilla—nearly any diminutive spring-flowering bulb—are charming growing in cracks around the flagstones.

Pockets of gritty soil between the stones give them the footing they need, and they will like the heat retained by the flagstones. Alpine bulbs also thrive at the sunny base of a rock wall or even in the chinks between the rocks of a dry-laid (unmortared) wall.

All of the miniature, hardy spring- and summer-flowering bulbs, including the small alliums, Greek anemones, most tulip species, and the miniature early bulbs recommended for meadow and woodland gardens are appropriate for rock gardens and other spots that afford them rock-garden conditions.

In the Mediterranean-climate areas of California, rock gardens make cultivation of scores of winter-growing, summer-dry bulbs easy, because drainage is fast, and mild winters and dry summers allow them to stay in the ground the year around. These bulbs include ixias, freesias, geissorhizas, romuleas, calochortuses, brodiaeas, babianas, winter-growing gladiolus, many moraeas, and Bulbinella floribunda.