Fertilising guide
How to fertilise Black Mondo Grass (Ophiopogon planiscapus 'Nigrescens')— schedule & NPK
Also called black mondo grass, black lilyturf.
More about black mondo grass
About Black Mondo Grass
Ophiopogon planiscapus 'Nigrescens' · also called black mondo grass, black lilyturf · houseplant
Ophiopogon planiscapus 'Nigrescens' is a striking evergreen perennial grown for its almost-black, strappy foliage, among the darkest of any garden plant. It forms slow-spreading clumps, bears pale lilac summer flowers and glossy black berries, and combines dramatically with silver or chartreuse plantings. Slow-growing and shade-tolerant, it suits edging, gravel gardens and containers.
Growth habit: Evergreen, slowly stoloniferous clump-former. Sends up tufts of arching, near-black leaves and gradually colonises by short runners to form low, dense mats over time.
What fertiliser black mondo grass actually wants — and why
Black Mondo Grass is an easy, light foliage feeder — a half-strength balanced liquid feed through the growing months keeps it green without forcing weak, sappy growth.
A balanced general houseplant feed (roughly even N-P-K) is exactly right — it is grown for foliage, so steady, moderate nitrogen for healthy leaves is the goal, not a bloom or root formula.
For the language behind the three numbers on the bottle — what nitrogen, phosphorus and potassium each do — see the NPK ratio explained entry. The short version for black mondo grass: match the feed to the job the plant is doing right now, not to a generic “plant food” on the shelf.
How often to feed black mondo grass, and which months
Feeding only earns its keep while the plant is in active growth and can use the nutrients — pour feed into a dormant or low-light plant and it simply builds up as root-burning salt. For black mondo grass:
Light feeder. A single spring application of balanced slow-release fertiliser or a mulch of leaf mould is sufficient. Indoors, feed monthly at half strength in the growing season; avoid heavy feeding. Treat that as monthly between spring through early autumn (roughly March to September); ease off in autumn and stop entirely in the low light of winter.
The dormant-season rule matters more than the exact interval: skip feeding entirely when black mondo grass is resting. For the wider context on indoor feeding rhythms across the seasons, the houseplant fertiliser schedule walks through the year month by month.
What strength to mix for black mondo grass
Half strength is the safe default for black mondo grass — houseplant feeds are formulated strong, and the diluted dose is gentler on the roots while still ample for foliage.
Feeding always goes onto already-damp soil, never dry roots — water black mondo grass first if the soil is dry, then apply the diluted feed. The companion question is when to water at all, covered in the black mondo grass watering schedule.
Signs you are over-feeding black mondo grass
Over-feeding is far more common — and more damaging — than under-feeding for most plants. The classic tells for black mondo grass:
- Brown, crispy leaf tips and edges with no sign of underwatering.
- A white, crusty salt deposit on the soil surface or pot rim.
- Weak, pale, stretched new growth that flops.
- Lower leaves yellow and drop while the soil is correctly watered.
Signs you are under-feeding black mondo grass
- Uniformly pale or yellow-green leaves, oldest first.
- Noticeably small new leaves and stalled growth in good light and season.
- A generally tired, lacklustre look despite correct watering and light.
If the symptoms point at watering, light or roots rather than nutrition, the full black mondo grass care brief covers soil, humidity and the common problems for this species.
Flushing and leaching the salts
Flush the pot of black mondo grass with plain water until it runs freely from the base every couple of months in the feeding season — it washes out the fertiliser salts that cause brown tips.
Organic vs synthetic feeds for black mondo grass
Organic options
A diluted seaweed or worm-casting feed, or fish emulsion if you can tolerate the smell indoors. UK: Westland or Baby Bio Organic, dilute seaweed; US: Espoma Indoor! or Neptune's Harvest fish & seaweed. Slow, gentle and hard to overdo.
Synthetic / liquid feeds
A general-purpose houseplant liquid at half strength — UK: Baby Bio, Westland Houseplant Feed or Phostrogen; US: Miracle-Gro Indoor Plant Food or Schultz. Convenient and fast-acting; the only risk is overdoing it.
Brand names are examples, not endorsements, and UK and US ranges differ — check the label’s own NPK and dilution rate, since formulations change.
Fertilising black mondo grass — frequently asked questions
What fertiliser does black mondo grass need?
A balanced general houseplant feed (roughly even N-P-K) is exactly right — it is grown for foliage, so steady, moderate nitrogen for healthy leaves is the goal, not a bloom or root formula. Black Mondo Grass is an easy, light foliage feeder — a half-strength balanced liquid feed through the growing months keeps it green without forcing weak, sappy growth.
How often should I feed black mondo grass?
Light feeder. A single spring application of balanced slow-release fertiliser or a mulch of leaf mould is sufficient. Indoors, feed monthly at half strength in the growing season; avoid heavy feeding. Light feeder. A single spring application of balanced slow-release fertiliser or a mulch of leaf mould is sufficient. Indoors, feed monthly at half strength in the growing season; avoid heavy feeding. Treat that as monthly between spring through early autumn (roughly March to September); ease off in autumn and stop entirely in the low light of winter.
What strength of feed for black mondo grass?
Half strength is the safe default for black mondo grass — houseplant feeds are formulated strong, and the diluted dose is gentler on the roots while still ample for foliage.
What does over-feeding black mondo grass look like?
Brown, crispy leaf tips and edges with no sign of underwatering. A white, crusty salt deposit on the soil surface or pot rim. Weak, pale, stretched new growth that flops. Lower leaves yellow and drop while the soil is correctly watered. Feeding black mondo grass year-round on a fixed schedule, including dark winter months, is the most common mistake — it cannot use the nutrients in low light and the surplus simply burns the roots and crusts the soil.
Should I flush the soil of black mondo grass?
Flush the pot of black mondo grass with plain water until it runs freely from the base every couple of months in the feeding season — it washes out the fertiliser salts that cause brown tips.
Keep reading
- Black Mondo Grass care — the full brief (light, soil, humidity, problems, pet safety)
- How often to water black mondo grass — the watering schedule
- The houseplant fertiliser schedule — feeding through the year
- NPK ratio explained — what the three numbers on the bottle mean
- How to fertilise snake plant
- How to fertilise dracaena
- How to fertilise peperomia
- All 3899 fertilising guides in the Growli library