Ornamental · Asparagaceae
Black Mondo Grass
Ophiopogon planiscapus 'Nigrescens'
Few plants come this close to true black, and a little sun is all it takes to keep the leaves at their darkest.
Full sun
Every 3–7 days
USDA 6–9
6–12 in · 15–30 cm
Overview
Black mondo grass is one of those rare plants with foliage so close to true black that designers reach for it again and again, and you can enjoy it just as much in your own garden. The arching grass-like leaves begin a deep green-purple and darken as they mature, and because it is an evergreen perennial, it holds that color right through the year. Despite the name, it is not actually a grass at all but a member of the asparagus family, native to Japan.
You will find it a slow, well-behaved groundcover that spreads on short underground runners, growing wider by inches rather than feet, so it never crowds out its neighbors. That gentle habit makes it easy to place: edging a path, slipping between stepping stones, or massed together at the front of a border where its dark color can shine.
Best of all, it is tough where it counts. It shrugs off cold down to 0°F (-18°C), asks for very little once it has settled in, and stays handsome with hardly any fuss. Give it decent soil, steady moisture, and enough light to keep the leaves dark, and it will hold its own for years.
Care
The short version: give black mondo grass anywhere from full sun to part shade for the blackest leaves, keep its soil rich and evenly moist but never waterlogged, and tidy away the old foliage in late winter. That is genuinely all it needs.
Light
Aim for full sun to part shade and you will get the darkest leaves; in deep shade the color tends to drift toward green. If you garden somewhere hot, a touch of afternoon shade is welcome, but otherwise more light means deeper color.
Water
Keep the soil evenly moist, which usually means watering roughly every 3 to 7 days during dry spells. It does become drought tolerant once established, but steady moisture rewards you with the best color and growth.
Soil
Plant it in rich, humusy, well-drained loam that is slightly acidic, with a pH of 5.5 to 7.0. Working a little compost into the planting hole gives it a kind start.
Temperature
It happily handles anywhere from 0°F (-18°C) up to about 95°F (35°C), which covers zones 6 through 9. The evergreen leaves stay put through the cold and green up again in spring.
Humidity
Ordinary outdoor humidity suits it just fine, so there is no number to chase. Good drainage matters far more than the moisture in the air, and it is soggy ground, not dry air, that causes trouble.
Feeding
Feed lightly in spring with a balanced general-purpose fertilizer, or simply work in some compost. This is a low-demand plant, so heavy feeding does very little for it.
Pruning
Pruning is barely a chore. Just shear off the tattered or winter-worn leaves in late winter, right before new growth appears, and the clump comes back fresh and tidy.
Repotting
If you grow it in a container, lift and divide it every 2 to 3 years before the roots crowd the pot. A thinning center or growth that has slowed down is your gentle cue that it is time.
Size & spacing
Each clump reaches 6 to 12 inches (15 to 30 cm) tall with a spread of 8 to 12 inches (20 to 30 cm). Space plants about a foot apart for distinct clumps, or closer together when you want quicker groundcover.
When to plant
This is a hardy perennial for zones 6 through 9 that you plant once and simply leave to do its thing. Set it out in spring so it has a full season to settle comfortably, and look forward to small bell-shaped flowers 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
Black mondo grass is a wonderfully forgiving plant, and nearly every problem traces back to one of two things: too much shade or too much water. The trick is to read the early signs on the leaves and roots and act before a small thing has a chance to spread. Find what you are seeing in the list below and you will know just what to do.
Yellowing leaves and a clump that rots in wet soil
Yellowing leaves and a flopping clump usually mean the roots are sitting in standing wet, which can lead to root rot, and the good news is that you can turn this around. Gently dig and check the roots, since rotted ones feel soft and dark. Work in some grit or compost to open up the drainage, ease back on watering, and replant the healthy divisions somewhere the soil drains freely.
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
Fresh divisions that sit quietly for a good while are doing exactly what a slow grower does, so there is no need to worry. Divide in spring and the plant has the whole season to settle in before winter arrives. Keep the soil evenly moist while new roots form, and the kindest thing you can do is simply give it time rather than digging it up to check on it.
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
Take heart, because a thin, patchy look in the first season or two is simply how this gentle spreader behaves, not a sign that anything is wrong. It travels on short stolons and knits itself together over several seasons rather than racing across the bed. If you would like coverage sooner, set new plants closer together at about 4 inches apart, and lift and divide your established clumps to tuck pieces into any gaps.
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
If those striking dark leaves are drifting toward green, the plant is simply asking for more light, and that is an easy fix. Deep shade softens the color, while sunnier spots bring back the near-black tone you love. Move it somewhere brighter and the rich color usually returns; in hot regions a little afternoon shade is fine, but lean toward sun whenever you want the deepest color.
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 shiny trails point to slugs and snails, which love damp, shady corners and feed once the sun goes down. The simplest remedy is to step outside after dark and hand-pick them off. Clearing away leaf litter and other hiding spots makes your bed far less inviting, and you only need to reach for a slug control when the damage really starts to add up.
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
Here is reassuring news: black mondo grass is not toxic. It belongs to the asparagus family, not the dangerous true lilies it sometimes gets mistaken for, and the worst that might happen is a mild stomach upset from eating a lot at once. That makes it a comfortable choice for homes with pets and children.
Safe for
People · Cats · Dogs · Horses · Rabbits · Livestock · Birds
Cats None
Safe to share a home with; a curious cat that chews many blades might get a brief upset stomach, as with any plant eaten in quantity.
Dogs None
No real danger here, since there is no known toxin; a big mouthful could leave a dog briefly queasy and nothing more.
Horses Safe
Not toxic to horses; it carries none of the poisons of the true lilies it is so often confused with.
Rabbits Safe
Rabbits can graze it without harm, as nothing in it is poisonous and an occasional bite is perfectly fine.
Livestock Safe
Livestock are not at risk, since the plant holds none of the compounds that tend to trouble them.
Birds Safe
Safe for birds; poultry can peck at the leaves and small fruit with nothing to worry about.
People Safe
No risk while handling or gardening; a stray taste does no harm beyond the mild upset any non-food plant might bring.
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 tend to show up under the mondo grass name, and you can tell them apart by looking at leaf color, flower habit, and fruit.
Ophiopogon planiscapus 'Nigrescens'
The standard black mondo grass, whose arching grass-like leaves come up green-purple and ripen into a glossy near-black, among the darkest foliage of any perennial you can grow.
'Black Dragon' / 'Ebony Knight'
Trade names you will see on plants offering the same near-black foliage as 'Nigrescens'.
Ophiopogon japonicus (green mondo grass / dwarf lilyturf)
The common green-leaved species, with narrower leaves than Liriope, flowers mostly tucked out of sight in the foliage, and blue fruit rather than black.
Black-leaved Liriope (lilyturf)
A different genus altogether, Liriope, with broader leaves, flowers held on erect spikes above the foliage, and black fruit instead of 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 reliable way to make more of this plant, and the lovely part is that it keeps that prized dark color true every single time.
DivisionEasy
Spring · One growing season
Division is your dependable route, since this cultivar will not come true from seed. Split an established clump in spring and each piece keeps the black color while having the full season to settle, taking roughly one growing season to root and fill out.
Myths
Black mondo grass is a true grass.
It only looks the part. This is Ophiopogon planiscapus, a member of the asparagus family that happens to grow in a grass-like evergreen clump.
It is the same plant as green mondo grass or lilyturf.
They are genuinely distinct. Green mondo is the related Ophiopogon japonicus, while lilyturf belongs to the separate genus Liriope with broader leaves and flower spikes that rise above the foliage; black mondo's narrow leaves and hidden flowers set it apart.