Elegant Silvers

Although we call all of them silvers, their silveriness varies from near glittering white and absolute silver to green-gray, grays, and silvery blues, and from spotted and streaked leaves to types covered with a metallic sheen. Silvers can be found in most plant groups, although few true annual species exist, since these occur mostly in winter rainfall areas where conditions are unfavorable to silver adaptation. We think of many of the silvers, such as the dusty millers (senecios), as annuals, but they are actually shrubby perennials in their warm, native climate. Although silvers are represented in many families in the plant kingdom, they are especially well represented in the sun-loving family Asteraceae. Silver plants dominate some genera (green plants are the exceptions among artemisias), while in others, they are anomalies. Their natural habitats around the world range from dry deserts to rain forests, from treeless plains swept by searing winds and intense heat to frigid mountain tops, rocky cliffs, and salt-sprayed coastlines. Some silvers even grow in alpine bogs. They live and thrive in such forbidding conditions because they have adapted to their environment by becoming silver.

Silvers are of three types: downy, waxy, and variegated. With the recent introduction of new silvery pulmonarias, heucheras, ferns, and brunneras, variegated plants have assumed more importance. While downy and waxy types are predominantly sun-lovers, variegated silvers thrive in shade, so their inclusion in the silver palette greatly extends landscaping possibilities.

Silver plants encompass the spectrum from tiny, compact alpines to soaring evergreens. Leaves can be long and thick or small and dainty, curled, cupped, or needlelike, with textures from soft and velvety to hard and leathery. Some plants are deeply rooted to anchor them from the wind and to enable them to draw down, others spread wide (as in a desert) for moisture. Many silvers contain toxic sap, give off sharp aromas, or display forbidding thorns to discourage hungry animals, for silvers inhabit difficult terrain where it pays to be armed. The world of silvers is complex and can be confusing, but if you enter it with a basic knowledge of the general types and the special language used to describe them — the vocabulary of silvers — hunting for the right silver for the right place will be a rewarding endeavor.

Plants within the downy group, the largest of the three, spring to mind when we hear the phrase "silver plant." Leaves (in some cases, the entire plant) are covered with a protective layer of down or hairs over the plant's natural green. The length, density, and position (upright or flattened), and the plant's exposure to bright sun determines the plant's coloring through all the shades of silver from near white and sterling to green-grays. The function of down is to maintain a layer of humidity close to the plant's surface that protects it from extremes of heat and cold. The effect is to create an aura or glow around the plants as sunlight bounces off their hairs, causing them to look silvery. Such plants, tough by design and beautiful in their impact, exist and flourish in seemingly impossible conditions.

More than 200 species of artemisias cope very well with the dry, blazingly hot summers and cold, windy winters that characterize vast expanses of treeless sagebrush, steppe country, or seacoast around the world, from the American West to southern Russia and North Africa. We tend to think of downy types as true silvers, because they are so unequivocally silver in appearance. In addition to artemisias, plants that quickly come to mind are the stachys, helichrysums, verbascums, as well as aromatic herbs and flowering plants whose blooms complement silver foliage, such as lavenders, salvias, santolinas, and perovskia.

One way to learn about the cultural needs or appearance of a particular downy type is to learn to "read" the plant through its Latin description: Thymus pseudolanuginosus describes a type of thyme that is rather woolly, a rough translation of pseudo (rather) and lanuginosus (woolly). A rule of thumb is that the hairier the plant, the drier growing conditions it requires. From just a name, the gardener knows that woolly thyme is covered in thick down and needs sharp drainage. Other instructive Latin epithets in the downy vocabulary include cinereus or cinerascens (gray); argentea, argenteus, and argentus (silver); and albi, albo, and albus (white).

Some downy silvers, often the most striking ones, have silver-backed foliage characterized by a polished, silvery sheen. In this kind, collapsed hairs — seen only with a magnifying glass — form what is called scale. Depending on their shape, or degree of curling or cupping, the least rustle of wind can turn up the leaves' undersides, sending out dramatic waves of silvery shimmers that dominate the entire landscape, as in the swaying foliage of a poplar or the mass of upturned leaves on the lilting stems of a buddleia bush. Scale can also cover entire leaves, as in epiphytic tillandsias, where it plays a vital role in retaining and absorbing moisture and nutrients from the atmosphere.