While any species of Artemisia, a genus in the aster family, may be commonly called wormwood, a ground-cover wormwood suggests a low, prostrate-growing plant. One species goes by an alternate name of silvermound (Artemisia schimidtiana) and develops a short, mat-like mound of silvery foliage to use in the rock garden or perennial border.
Silvermound, a ground-cover-like wormwood species, hails from Japan. It grows in dry fields, meadows and scrub in sunny openings of forests in well-draining soils that are non-acidic.
Growing from underground rhizomes, this ground-cover wormwood develops into a tufted mass of finely textured foliage. Fern-like leaves display a silky, hairy surface of silvery white and the leaves have deeply cut linear lobes. In summer, small yellow flower heads that look like daisy centers lacking any petals appear above the mass of foliage, attracting bees and butterflies. It reaches a mature size of 12 inches by 20 inches, remaining evergreen (leaves persistent) across winter if the weather is not too severe.
Silvermound prosper when grown in full sun exposures, receiving more than eight hours of direct sunlight daily. The soil must be fertile and fast-draining after rains or irrigation. Typically it grows well in neutral to alkaline soils (pH 7.0 and higher). In acidic soils or heavy clay soils, grit and organic matter improves water drainage, but the plants may be short-lived if soil remains too moist or ambient humidity too high across summer. Trim back stems in autumn if desired to allow for rejuvenation of leaves in spring and to keep plants compactly shaped and more appropriate as a low ground cover.
Abundant rainfall, high ambient humidity, poor air circulation and inadequate sunlight leads to fungal problems on wormwoods, including the silvermound. White rust, powdery mildew and leaf and stem rots occur. This perennial grows best only in regions rated USDA hardiness zones 5 through 8, and elsewhere works well only as a seasonal annual plant. University of Georgia perennial plant expert Dr. Allan Armitage comments that the center of the plant tends to "melt out" or become barren and brown in long, hot or humid summers even in USDA zones 7 and 8. He recommends taking cuttings in midsummer to replenish gardens with new plants.
One cultivated variety of Artemisia schmidtiana particularly fulfills the need to form a low ground cover: Nana, or sometimes synonymously labeled as variety Silver Mound. This selection grows merely 3 inches tall but spreads to 12 inches; planting numerous plants 10 inches center-to-center develops a larger, uniform, carpet-like effect in the sunny garden.
Although a different species, another possible ground cover wormwood choice is Artemisia stelleriana, Broughton Silver, also sold as Silver Brocade or Mori. This plant grows 6 inches tall and 12 to 18 inches wide.