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Herbs for Ground Covers
Several herbs can become attractive ground or bank covers. Drought resistant herbs such as rosemary and thyme perform well in dry, sunny areas that would not support more sensitive plants. Sweet woodruff and most of the mints do well in moisture and shade and make attractive ground covers in woodland landscapes. Some others notably chamomile can be mowed and walked on as a lawn substitute.
Rosemary. Rosemary makes a 0.5-1.5m ground cover depending on the variety and how it is trimmed. R. officinalis 'Collingwood Ingram' grows to about 60-90 cm tall, and the gracefully curving branches spread 1.2m or more along the ground. Rich, bright blue-violet flowers cover most of the foliage in the summer, making it a colorful, tall, bank cover. R. o. 'Lockwood de Forest' resembles the prostrate variety but has lighter foliage and bluer flowers. R. o. 'prostratus' or dwarf rosemary hugs the ground closely, usually growing only 30-60cm tall and spreading to 1-2m. The stems of this variety will spill nicely over ledges and walls.
All of these rosemaries can endure hot sun and poor soil, but good drainage is a must. Once established they need little or no watering except in the desert. Feeding and excess watering result in rank growth and woodiness,
and eventual death. Control their growth by frequent tip pinching when the plants are small. Older plants will need occasional light pruning to keep them looking neat; make all cuts to the side branches. For a ground cover, set small rosemary plants about 60cm apart. For quick growth, feed lightly and head back new growth periodically to encourage bushiness.
Thyme. Like rosemary, thyme grows in warm, light, well drained soil and full sun. It can withstand a fair amount of neglect. As ground covers, the thymes grow lower than the rosemaries and have more matted foliage. Woolly thyme (T. lanuginosus) forms a flat to undulating mat 5-8cm high of dense, small woolly leaves. This species is best for covering small areas (including difficult ones) but is not for large areas because the plants tend to become rangy in winter. Caraway scented thyme (T. herba-barona) forms a thick, flat mat of dark green, 2cm long leaves that have a caraway odor. T. serpyllum or creeping thyme forms a thick mat 5-15cm high and will withstand occasional foot traffic.
As a ground cover, plant the thymes 15-30cm apart in the fall or spring and restrain them as needed by trimming back the growing tips.
Germander. Prostrate germander (Teucrium chamaedrys `prostratum') is a tough herb that likes sun and heat and will endure poor, rocky soils. It grows 15-30cm high and spreads to about 60cm.
Shady areas that receive little sun are sometimes difficult to cover. Sweet woodruff (Asperula odorata) is a low-growing herb with spreading stems15-30cm high. The whorls of rich green leaves are attractive in woodland settings. It loves shade and moisture and grows best in a rich soil.
Corsican mint (Mentha requienii) is another woodsy ground cover with interesting foliage. It grows only 1cm high, and the tiny round bright green leaves have a mossy effect. It spreads at a moderate to rapid rate if given shade and plenty of water.
There are several herbs that can be grown as lawn substitutes. chamomile (Anthemis nobilis) is a traditional ground cover for paths and walkways in herb gardens. It forms a soft-textured, spreading, 10-30cm mat of light green, finely cut leaves. If mowed occasionally, it can be kept short enough to serve as an aromatic lawn. Plant divisions 30cm apart in full sun or very light shade and water moderately.
Cotula (Cotula squalida), though not an herb, often is substituted for chamomile in most Western States. Its growth habit is similar to chamomile and the leaves are soft, hairy, and fernlike with a bronzy green color. It is sometimes called brass buttons because of the yellow, button like flowers that can be kept mowed down for a flat surface.