Can You Use Oxalis As a Ground Cover?

Widely Spreading Ground Covers

• Those oxalis species that grow through rhizomes, or horizontal stems on or just below the surface, spread more easily than those that grow from tubers or bulbs. Growing in U.S. Department of Agriculture plant hardiness zones 7 through 9, redwood sorrel, also called Oregon oxalis, (Oxalis oregana) is one of the faster and potentially invasive types, with 10-inch tall, lavender-veined leaves. Wood sorrel or shamrock (Oxalis acetosella), hardy in USDA zones 6 through 11, also grows fast and spreads widely.

Non-Invasive Oxalis

• Purple shamrock (Oxalis triangularis), which grows in USDA zones 6 through 10, forms 12-inch tall wide mounds that do not spread further than 18 to 24 inches. Also with dark burgundy leaves that appear almost black, volcanic sorrel (Oxalis vulcanicola "Zinfandel") forms an even smaller mound: 6 to 10 inches tall and 12 inches wide. Its bright yellow flowers stand out sharply against the dark leaves.

Planting Oxalis

• Oxalis grow either from seed or from nursery plants. Sow the seeds in late winter or early spring, once temperatures are above 55 degrees Fahrenheit, or plant tuberous oxalis about 1 inch deep and 3 to 5 inches apart. Because both redwood sorrel and wood sorrel form a dense ground cover, plant them further apart than you would oxalis grown from tubers of bulbs, about 10 inches apart.

Growing Oxalis

• All types of oxalis grow best in full sun or partial shade with rich, moist soil that has plenty of organic matter. They need regular water, about once a week. It's possible to slow down the growth of invasive types by watering less often, about once every two weeks, and by growing the plants in densely shaded areas. For new plants, pinch off the small, new plants formed at the base of running stems or divide large clumping plants in the spring.