Plant black mondo grass (Ophiopogon planiscapus "Nigrescens") along walkways, or use this striking perennial as a ground cover in perennial flower beds or shrub beds. In containers, the purple-black foliage creates striking contrast alone or with other perennials. You can grow black mondo grass in U.S. Department of Agriculture plant hardiness zones 5 through 10.
Black mondo grass leaves typically grow 6 to 9 inches long, but can grow up to 15 inches long. The leaves arch gracefully, creating a soft, low ground cover. To create a dense planting, space plants 3 to 6 inches apart. The leaves are dark purple to black, creating a dramatic visual effect. In late summer, tiny pink to purple flowers bloom along arching stalks above the leaves, creating a delicate contrast.
Growing Regions and Hardiness
If you live in mild areas of the growing zone, with mild frost or no winter frost, black mondo grass will grow year-round as an evergreen. In areas with heavy winter frosts and snow, the plants will die back in winter but will come up again in spring from the roots. Though technically hardy in USDA zone 5, it's a good idea to plant black mondo grass in a protected area in USDA zone 5.
You can grow black mondo grass in full sun, where it gets six or more hours of sun a day, or in part shade with two to four hours per day. This makes it a good choice for transition zones where the garden changes from sun to shade. Black mondo grass grows well in loamy soil and needs regular moisture to thrive. Water once a week, soaking the roots deeply each time. Plan to provide about 1 inch of water per week. In hot weather, feel the soil 1 to 2 inches deep and water when it starts to dry out.
Fertilize twice a month using a balanced, liquid fertilizer, like a 10-10-10 or 20-20-20 formula. Add 1/2 tablespoon to 1 gallon of water for each plant and then pour it onto the soil around the base. Black mondo grass is mostly pest-free, but you might find an occasional slug or snail on the plants. Just pick them off so they don't damage the leaves.
Dividing and Transplanting
Every two to three years, divide black mondo grass to prevent overcrowding. Dig out the clumps 12 inches deep. To get as much of the roots as possible, dig 8 inches from the base of each plant. To divide, simply pull the plants into two or three sections, and then replant each section. You can use the divisions to create a new planting somewhere in the garden, or pot them up to give away is you have more than you need.