Ornamental · Asparagaceae
Black Mondo Grass
Ophiopogon planiscapus 'Nigrescens'
Few plants come this close to true black, and a little sun keeps the leaves at their darkest.
Full sun
Every 3–7 days
USDA 6–9
6–12 in · 15–30 cm
Overview
Among the very few plants that read as genuinely black, this one has long been a designer's quiet luxury. The arching, grass-like leaves start a deep green-purple and settle into a near-black with age, an evergreen perennial that holds its color through every season. Despite the look, it is not a grass at all but a member of the asparagus family, native to Japan, which is part of why it carries itself with such unexpected polish.
As a groundcover it is slow and beautifully well-mannered. It moves on short underground runners and gains ground by inches rather than feet, so it never elbows out its neighbors. That restraint makes it a natural along a path edge, threaded between stepping stones, or massed at the front of a border where you want a clean dark line to anchor everything planted behind it.
It is tough where it counts, cold-hardy to 0°F (-18°C) and undemanding once it has settled in. Give it decent soil, steady moisture, and enough light to keep the leaves dark, and it will stay elegant year after year with very little asked of you in return.
Care
The short version: site it in full sun to part shade for the blackest leaves, keep the soil rich and evenly moist but never waterlogged, and tidy away the old foliage in late winter.
Light
Plant it in full sun to part shade for the darkest leaves; sink it into deep shade and the color drifts toward green. In hot regions a touch of afternoon shade keeps it comfortable, so pick a spot that catches good light without baking through the worst of the day.
Water
Keep the soil evenly moist, watering roughly every 3 to 7 days through dry spells. It will tolerate drought once it is established, but a steady supply of moisture is what gives you the best color and the most growth.
Soil
It wants a rich, humusy, well-drained loam on the slightly acidic side, around 5.5 to 7.0 on the pH scale. Work some compost into the bed at planting time and it settles in happily.
Temperature
It takes the range from 0°F (-18°C) up to roughly 95°F (35°C), comfortably covering zones 6 through 9. The foliage stays evergreen through the cold and refreshes itself in spring.
Humidity
Ordinary outdoor air is all it needs, with no number worth tracking. What matters far more than moisture in the air is drainage at the roots, since it is soggy ground, not dry air, that does the damage.
Feeding
A light spring feed of a balanced general-purpose fertilizer or some compost is plenty. This is an undemanding plant, and piling on more does little to improve it.
Pruning
There is hardly any upkeep here. Shear off the tattered or winter-worn leaves in late winter before the new growth appears, and the clump comes back fresh and clean.
Repotting
Grown in a container, lift and divide it every 2 to 3 years before the roots crowd the pot. A center that thins out or growth that slows down is your cue that it is time.
Size & spacing
Each clump stands 6 to 12 inches (15 to 30 cm) tall and spreads 8 to 12 inches (20 to 30 cm) wide. Set them a foot apart for distinct, well-defined clumps, or tighter when you want quicker cover.
When to plant
This is a hardy perennial for zones 6 through 9, the kind of plant you set once and leave to do its thing. Put it in the ground in spring so it has a full season to find its feet, and look for small bell-shaped flowers to arrive in summer, from July into August.
Northern hemisphere
Southern hemisphere
Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.
- Plant: spring
- Harvest: summer (July to August)
Hardiness
USDA hardiness zones: 6–9
Temperature: down to -23°C
Troubleshooting
For such an easygoing plant, the short list of troubles almost always comes down to too much shade or too much water. Watch the leaves and the roots for the early tells, and step in before a small issue has a chance to spread through the planting.
Yellowing leaves and a clump that rots in wet soil
Ground that stays wet at the roots invites root rot, and the first sign is foliage that yellows and slumps. Lift the clump and feel the roots; healthy ones are firm, while damaged ones turn soft and dark. Work grit or compost into the bed to open the drainage, ease back on extra watering, and replant the sound divisions somewhere the water moves through freely, such as a slightly raised spot.
Fix:
- Improve drainage by amending soil with organic matter or grit
- Reduce supplemental watering when soil stays wet
- Replant healthy divisions in a better-drained, raised, or amended site
Weak, slow regrowth after dividing
A slow grower picks up slowly, so fresh divisions can sit quietly for a while before showing any new push. Time the job for spring and they get the whole season to settle in before the cold arrives. Keep the soil evenly moist while new roots take hold, and give the pieces the patience they need rather than lifting them again to check.
Fix:
- Divide in spring so plants have the full season to re-establish before winter
- Keep soil evenly moist while new roots form
- Allow extra time for recovery rather than disturbing again
Slow to spread and fill in as a groundcover
Filling in slowly is simply how this plant behaves, not a problem to fix. It travels on short stolons and needs several seasons to knit into a continuous mat, so an open, spotty look in the first year is exactly what you should expect. If you want coverage sooner, set young plants closer together at about 4 inches apart, and lift and divide established clumps to fill the bare patches in between.
Fix:
- Be patient and allow clumps to establish over several seasons
- Plant more closely (about 4 in apart) when a faster groundcover effect is wanted
- Divide established clumps to make more plants and fill gaps
Black leaves washing out toward green
When the leaves slide back toward green, the spot is usually too dim. Sun drives the dark color, and a plant tucked into deep shade will read green rather than the inky black you wanted in that corner. Shift it to a brighter position and the near-black returns over the season. In hot regions a little afternoon shade is welcome, but lean toward sun where you want the color to hold.
Fix:
- Move or transplant to a brighter, sunnier location
- In warm climates provide some afternoon shade but otherwise favor sun for color
Ragged, chewed leaves with slime trails
Ragged holes and a telltale shine across the foliage point to slugs and snails, which work after dark in the damp, shady pockets these plantings often create. Pick them off by hand once the sun is down, and tidy away the leaf litter and cool hiding places that draw them in. Save a slug control for the spots where the damage genuinely keeps mounting.
Fix:
- Hand-pick slugs and snails in the evening
- Remove debris and reduce excess moisture and hiding spots
- Use slug controls where pressure is heavy
Toxicity
This is not a toxic plant. It belongs to the asparagus family, not the dangerous true lilies it is so often mistaken for, and the worst it tends to cause is a mild stomach upset from a big helping. That makes it a relaxed choice for homes with curious pets and children.
Safe for
People · Cats · Dogs · Horses · Rabbits · Livestock · Birds
Cats None
Safe to share a room with; a few blades nibbled in passing might bring on a brief upset stomach, the same as any plant eaten in quantity.
Dogs None
No real danger here, with no known toxin; a large mouthful could leave a dog briefly queasy, nothing more.
Horses Safe
Not toxic, and free of the poisons found in the true lilies it tends to be mistaken for.
Rabbits Safe
Can graze on it without harm; nothing here is poisonous, so an occasional bite is fine.
Livestock Safe
Not at risk, since the plant carries none of the compounds that trouble grazing animals.
Birds Safe
Safe around backyard poultry, which can pick at the leaves and small fruit without worry.
People Safe
No risk in handling or planting it; a stray taste does nothing beyond the mild upset any non-food plant might cause.
No special handling required; as with any plant, discourage pets from eating large quantities to avoid mild stomach upset.
Varieties
A handful of selections and look-alikes go by some version of the mondo grass name. The reliable way to tell them apart is by leaf color, how the flowers are carried, and the color of the fruit.
Ophiopogon planiscapus 'Nigrescens'
The standard black mondo grass, with arching grass-like leaves that emerge green-purple and mature to a glossy near-black, ranking among the darkest foliage of any perennial.
'Black Dragon' / 'Ebony Knight'
Trade names offered for the same near-black foliage you get from 'Nigrescens'.
Ophiopogon japonicus (green mondo grass / dwarf lilyturf)
The common green-leaved species, with narrower leaves than Liriope, flowers mostly hidden down in the foliage, and blue fruit in place of black.
Black-leaved Liriope (lilyturf)
A different genus, Liriope, with broader leaves, flowers carried on erect spikes above the foliage, and black fruit rather than the blue of green mondo grass.
Companions
Plant near
Chartreuse or gold-foliage plants (e.g., golden creeping Jenny, Hakone grass 'Aureola'): Bright lime/gold foliage gives strong color contrast against the near-black leaves.
Silver or gray foliage plants (e.g., lamb's ear, dusty miller): Silver tones highlight the dark foliage for dramatic contrast in borders and containers.
How to propagate
There is one dependable way to make more of it, and it has the happy advantage of keeping that coveted dark color true every single time.
DivisionEasy
Spring · One growing season
Since it will not come true from seed, division is the way to make more. Split an established clump in spring and every piece keeps that coveted black color, with a full season ahead to settle in and fill out, which takes about one growing season.
Myths
Black mondo grass is a true grass.
It only plays the part. This is Ophiopogon planiscapus, a member of the asparagus family, not a grass at all, even though it settles into a low, grass-like evergreen clump that reads as one in a planting.
It is the same plant as green mondo grass or lilyturf.
They get muddled but stay distinct. Green mondo is the related Ophiopogon japonicus, and lilyturf is the separate genus Liriope with broader leaves and flower spikes held up above the foliage, while black mondo sets itself apart with narrow leaves and flowers tucked out of sight.