Composed of very fine particles, clay soil can test any gardener’s patience. Nearly impenetrable in drought and slow to drain when saturated, it may starve roots of nutrients or drown them. Amending clay with organic matter like peat, straw or bark improves its pliability and drainage, according to Colorado State University Extension’s associate professor J. G. Davis and horticultural agent C. R. Wilson. Another option is to choose ornamental plants that tolerate--or thrive in--clay.
Blue mistflower (Conoclinium coelestinum), an aster family perennial, brightens gardens with its mid-summer to mid-autumn blooms. Standing up to 3 feet high, it has triangular green leaves on erect stems. Its yellow-centered, stem-topping flowers occur in flat clusters. The tiny--1/4 inch-- blue or purple blossoms are butterfly and bee favorites, according to the Lady Bird Johnson Wildflower Center. A common sight along stream banks and woodland edges in the Mid-Atlantic, Midwestern and Southern United States, blue mistflower spreads quickly. It likes moist soils, including clay, and full sun to partial shade.
Coastal Sweet Pepperbush
A narrow, clumping shrub, coastal sweet pepperbush (Clethra alnifolia) handles a range of acidic (pH below 6.8) moist or wet soils, including clay. Its pest and disease resistance equals its soil adaptability. Standing from 6 to 12 feet high, it has upright stems and green foliage with muted yellow or orange autumn color. In July and August, coastal sweet pepperbush attracts hummingbirds and butterflies with its clusters of columnar white flower spikes. Brown seedpods follow the sweetly scented blooms. Native to coastal areas and swamps throughout the Eastern United States, the plant grows in full sun to shade, according to the Lady Bird Johnson Wildflower Center.
Aster 'Wood's Purple'
An aster family perennial hardy to minus 30 degrees Fahrenheit, aster (Aster) ‘Wood’s Purple’ grows up to 18 inches high and wide. A versatile plant, it thrives in well-drained, moderately moist sandy or clay soils, according to the Missouri Botanical Garden. Its mounding form has multiple stems with glossy green leaves and late summer or early fall blooms. The bluish-purple to purple, yellow-centered flowers light sunny areas when many other garden plants are fading. This disease-resistant aster performs best in full sun.
Ornamental switchgrass (Panicum virgatum) ‘Squaw’ stands 3 to 4 feet high and up to 2 feet wide. Desirable for its three seasons of garden interest, it has deep red spring and summer foliage. Appearing in July, its red flowerheads fade to beige in the fall, according to the Missouri Botanical Garden. Flowers and foliage--which ages to brown--last into winter. Squaw makes an attractive accent or screening plant. It grows in sun or partial shade and moist clay or sandy soil.