Poor soil doesn't have to be bare soil. Many useful ground covers will grow in soils lacking in fertility and organic matter. Some plants even grow better in poor soils than they do in rich ones.
Also known as common bearberry and kinninnick, bearberry (Arctostaphylos uva-ursi), which grows in U.S. Department of Agriculture plant hardiness zones 2 through 7, prefers infertile soils. This broad-leaf evergreen grows to 1 foot high and creeps slowly to a spread of 3 to 6 feet. It has pinkish white flowers in spring, and the leathery green foliage turns bronze in fall.
Although not a true fern, sweetfern (Comptonia peregrina) is a shrub with frondlike foliage that can grow in soils most plants would find inhospitable. Growing in U.S. Department of Agriculture zones 2 through 6, it grows up to a 4 feet tall, spreading 4 to 8 feet wide by suckers. Sweetfern is deciduous.
'Low Boy' Prostrate Acacia
A low-growing shrub that spreads up to 15 feet wide, 'Low Boy' prostrate acacia (Acacia redolens 'Low Boy,' USDA zones 9a through 11) thrives in hot and dry areas. With gray-green leaves and small yellow flowers in spring, it remains under 1 foot tall and can help prevent erosion.
Japanese Garden Juniper
Japanese garden juniper (Juniperus procumbens 'Nana,' USDA zones 4 through 9) is a low-growing evergreen that tolerates drought as well as shallow rocky soil. With a mature height of 1 foot, its green-needled branches spread up to 6 feet.
Ground Morning Glory
Ground morning glory (Convolvulus mauritanicus, USDA zones 7 through 9) is an evergreen perennial that tolerates poor soils provided they are well-draining. A fast grower, 1 foot high and spreading 1 1/2 to 3 feet, it has fuzzy, blue-tinged foliage and lavender flowers spring to early fall.
Called wild thyme or mother-of-thyme, creeping thyme (Thymus serpyllum 'Pink Chintz,' USDA zones 5 through 8) makes a fragrant ground cover for smaller areas. It grows to a height of only 4 inches and 1 foot wide. Creeping thyme is covered in tiny pink blooms in summer.
Another ground cover for a small area with infertile but well-drained soil, stonecrop (Sedum rupestre, syn. Sedum reflexum, USDA zones 5 through 8) grows up to 6 inches high and 2 feet wide. Trailing types of sedum have small, succulent leaves and summer flowers.