Black mondo grass

Black mondo grass: how do you recognise it?

Habit

Low, dense tuft about 20 cm tall and 30 cm wide that slowly spreads by short underground runners.

Leaves

Narrow, strap-like and arching, 20–30 cm long; dark green in the species, almost black in ‘Nigrescens’.

Flower

Small bell-shaped flowers in short sprays among and just above the leaves, in July and August.

Colour

White to pale lilac-pink, lovely against the dark foliage.

Fruit

Round, glossy, blue-black berries that hang on into winter.

Roots

Fibrous, with small tuberous swellings here and there and short runners.

Flowering: July–August · Plants: March–May and September–October · Pruning: March

Why grow it?

• Evergreen: the dark foliage looks good twelve months a year.
• The almost black leaves of ‘Nigrescens’ make a striking contrast with silver, yellow or lime-green plants.
• A slow, tidy ground cover for edges, rock gardens, pots and between stepping stones.
• Small summer flowers and glossy berries well into winter.
• Little work: hardly any pruning and rarely any disease.

Black mondo grass: where does it grow best?

• Sun to partial shade. In sun the leaves stay darkest, as long as the soil does not dry out.
• Humus-rich, well-drained sandy or loamy soil, acid to neutral.
• Moderately moist: do not let it dry out and avoid standing water in winter.
• Plant closely, 15 cm apart, because it grows slowly.
• Also suitable for pots and containers on a patio.

Light

Sun and partial shade

Soil type

Sand or loam

Acidity

Acid or neutral

Moisture

Normal

Size

0.2 m tall, 0.3 m wide

Hardiness

Hardy (to -20 °C)

Goes well with

• Japanese forest grass: Its bright yellow-green leaves stand out sharply against the black.
• Spotted dead-nettle: Silvery leaves and low growth: together a strong contrast in partial shade.
• Snowdrop: White bells above the dark carpet in February.
• Coral bells: Forms with lime-green, silver or orange leaves complete the contrast.

Black mondo grass: when and how to plant it?

Plant in March–May and September–October.

1. Plant in March–May or September–October.
2. Loosen the soil and mix in some compost or leaf mould; in heavy soil add coarse sand as well.
3. Space the plants 15 cm apart, at the same depth as they were in the pot.
4. Firm the soil and water in thoroughly straight away.
5. Keep the soil moist in the first year, until the tufts are well established.
6. A thin layer of fine gravel or fine mulch keeps weeds down until the plants knit together.

Care

Watering

In dry spells in the first year; after that only in long dry periods, especially in sun and in pots.

Feeding

A thin layer of compost in spring is enough.

Tidying

In March, pull or cut away brown or damaged leaves.

Weeding

Weed carefully in the first years, until the tufts form a closed carpet.

Pots

Use potting compost with some coarse sand and a pot with a drainage hole. Repot every two or three years, or divide the plant.

Tip: The cultivar ‘Nigrescens’ has almost black leaves, lovely among silver or lime-green plants or on pale gravel. It grows slowly: plant closely, 15 cm apart.

Black mondo grass: when to prune it?

Pruning months: March.

When: Pruning is hardly needed. In March, clear away brown or damaged leaves before the new growth starts.

How:

• Cut or pull away dead, brown leaves at the base; fingers or a small rake work best.
• Never cut the whole tuft down: it grows slowly and recovers only slowly.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Division

In April: lift a clump, pull or cut it into pieces with a few shoots and roots each, and replant them straight away.

Runners

In spring, detach the young plants that form on short runners around the clump and plant them separately.

Seed

In winter, remove the flesh from ripe berries and sow straight away in a pot outdoors. Germination is slow and not all seedlings are equally dark.

Black mondo grass: how does it get through the winter?

Hardy to −20 °C.

• Hardy to about −20 °C: it gets through most Belgian winters without protection.
• In hard frost or cold wind the leaves may turn brown; new leaves grow in spring.
• In a pot: stand it against a wall and wrap the pot in hessian or bubble wrap during hard frost.
• Wet soil in winter is more dangerous than frost: make sure drainage is good.

Diseases and pests

• Slugs: They sometimes nibble young leaves in spring. Pick them off in the evening.
• Brown leaf tips: Caused by drought or cold wind. Water in dry spells and tidy away brown leaves in March.
• Root rot: Yellow, limp tufts in wet, heavy soil. Replant in a better-drained or slightly raised spot.
• Slow growth: Normal for this plant. Plant closely and be patient; extra fertiliser does not help.

Through the year

• January: Protect pots in hard frost.
• March: Cut away brown and damaged leaves. Plant.
• April: Plant and divide. Apply a thin layer of compost.
• May: Plant. Water in dry spells.
• July: Small lilac-pink bells in flower.
• August: Flowering. Water in dry spells, especially in pots.
• September: Plant. The berries colour up.
• October: Plant. Glossy blue-black berries.
• December: Berries and dark foliage decorate the winter garden.

Did you know?

• Despite its looks it is not a grass: black mondo grass belongs to the asparagus family.
• Plants with almost black leaves are rare; ‘Nigrescens’ is one of the best known in gardens.
• In Japan the related Ophiopogon japonicus is widely used as a green ground cover instead of lawn.