Ophiopogon planiscapus aka Black Mondo

Ophiopogon planiscapus, or mondo grass, is a perennial from Japan. Its native range covers central and southern parts of the country. It belongs to the asparagus family, despite its grass-like look. The plant forms dense tufts and spreads slowly by runners. Thickened roots support the clumps as they grow. Garden plants reach about 0.7–1 foot (0.2–0.3 metres) tall and wide. RHS gives a broader size range, reaching 1.6 feet (0.5 metres). Clumps can spread beyond their first width over time.

The narrow leaves arch out from the plant's base. They feel leathery and give the clumps a fine texture. RHS describes dark green leaves, as does Missouri Botanical Garden. NC State reports purple-black foliage on its species page. The leaves have smooth edges and lack hairs. RHS lists leaf lengths of about 0.7–1 foot (0.2–0.3 metres). The foliage stays green through the year in mild climates. Cold winters can leave the leaves worn or damaged.

Small bell-shaped flowers open in summer, from July to August. Their white petals may carry a pale lilac tint. Each flower has six tepals and sits in a raceme. Bare flower stalks lift these clusters above the leaves. The species name refers to the stalk's flat shape. Round, fleshy fruits follow the flowers and appear in autumn. Sources describe them as blue, blue-black, or glossy dark purple. Missouri Botanical Garden compares their size with a pea.

Grow mondo grass in rich soil with plenty of humus. Keep the soil moist, but allow excess water to drain. Slightly acid soil suits it; neutral soil also works. RHS lists clay, loam, and sand as suitable soil types. Sources allow sun or partial shade, though Missouri favors shade. Even moisture is preferred despite its listed tolerance of drought. USDA zones 6–9 and RHS H5 cover its stated hardiness. Plants may need shelter in colder parts of zone 6.

Use the clumps as ground cover, edging, or border plants. They also suit pots, rock gardens, and stream or pond edges. Their leaves provide the main interest in shaded beds. Divide plants in spring when new growth starts. Seeds can also be sown once ripe. Routine pruning is not needed. Serious pest and disease issues are uncommon, but slugs may cause damage. NC State also lists fern scale as a possible pest.