Grass-of-Parnassus

How to recognise it

Growth habit

Hairless perennial, 10–30 cm tall, with a leaf rosette at the base and one or a few unbranched flowering stems.

Leaf

Rosette leaves long-stalked, heart-shaped, untoothed and hairless, with a blade of 1–4 cm. Halfway up the stem sits a single stalkless, heart-shaped leaf that clasps the stem.

Flower

One white flower of 1.5–3 cm per stem, with five rounded petals marked with translucent, greenish veins. Between the five stamens are five scales, each with a fringe of threads tipped with glistening, yellowish-green knobs. From July to September.

Fruit/Seed

An egg-shaped capsule that splits open into four valves, with many small, light seeds spread by the wind.

Roots

A short rhizome with fibrous roots; the plant makes no runners and stays a loose rosette.

Confusion with

In flower it is hard to mistake: no other white flower has those fringed scales with glistening knobs. Without flowers the leaf rosette looks like that of a violet, but violets have scalloped leaf edges and no clasping leaf on the stem.

Flowering: July–September · Pruning: October

Why grow it?

• A late bloomer: from July into September, when little else is flowering in wet meadows and dune slacks.
• Flies, hoverflies, small bees and beetles visit the flowers; the glistening false nectar glands lure them in, while the real nectar is hidden at the base of the scales.
• A typical plant of wet, nutrient-poor, chalky places: where grass-of-Parnassus grows, the water is clean and the soil unfertilised.
• For a wet nature garden or a nutrient-poor pond edge with chalky sand, it is a beautiful but demanding flower for late summer.
• A plant with a remarkable structure: the stamens ripen one at a time and take turns to bend over the pistil.

Grass-of-Parnassus: where does it grow best?

• In the wild: damp dune slacks, alkaline fens, wet unimproved grassland, purple moor-grass meadows and seepages at the foot of slopes.
• Full sun to light part shade, in low, open vegetation; among tall grass or reeds it disappears.
• Always moist to wet, nutrient-poor soil, chalky or base-rich: sand or peat fed by lime-rich groundwater or seepage.
• In the garden: on the shallow, nutrient-poor margin of a pond, in a bog bed of poor, chalky sand, or in a wet, short-mown corner of a wildflower meadow.

Goes well with

• Fairy flax: A small, delicate plant with white flowers, typical of the same damp dune slacks and chalk grassland.
• Devil’s-bit scabious: Blue pompons in August–September, in the same wet, nutrient-poor grassland.
• Marsh helleborine: An orchid of damp dune slacks that flowers in July; only as a nursery-raised plant.
• Ragged-Robin: Pink flowers in May–June, before grass-of-Parnassus starts to flower.

Grass-of-Parnassus: when and how to plant it?

1. Buy plants or seed from a nursery for native plants; grass-of-Parnassus is not easy in the garden, so start with a few plants in a well-chosen spot.
2. Sow in September–November: scatter the very fine seed on a moist mix of poor sand and a little loam, without covering it, and leave the pot outside all winter. The seed needs a cold spell to germinate.
3. Plant in April–May or in September in a sunny, always moist spot, 15–20 cm apart, in poor, chalky soil; on acid soil, mix in some chalky sand or crushed shells.
4. Water after planting and make sure the soil never dries out, not even in summer.
5. No manure, compost or potting compost: on rich soil it is soon overgrown.
6. Never dig up or pick grass-of-Parnassus in the wild: the plant is rare and threatened, and its sites are fragile.

Care

Watering

The soil must always stay moist to wet. Water regularly in dry summers; drying out is fatal.

Feeding

Never. Rich soil or nutrient-rich water lets grasses, reeds and algae take over, and then grass-of-Parnassus disappears.

Mowing

Mow the spot once a year, in October, when the seeds have been shed, and remove the cuttings. This keeps the vegetation low and open.

Competition

Pull out young willows, reeds, rushes and vigorous grasses in good time: grass-of-Parnassus needs light right down to the ground.

Self-seeding

Let the capsules split open on the plant: new seedlings will then appear around the parent plant, on patches of slightly bare, moist soil.

Tip: Make a bog bed with poor sand and a little chalky material, without potting compost, and keep the water level up: this recreates a damp dune slack, where grass-of-Parnassus feels at home.

Pruning and mowing

Pruning months: October.

When: No pruning, just mowing: once a year in October, after the seeds have ripened.

How:

• Leave the spent stems until the capsules turn brown and split open.
• Mow short in October and remove the cuttings, so the soil stays poor.
• In a larger garden, leave a strip unmown until spring as shelter for overwintering insects.
• Now and then scratch open a small patch of bare soil, so the seeds can germinate.

Caution: Do not mow from July to September: that is when it flowers and the seed ripens.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Seed

Sow fresh seed in September–November outdoors in a pot of moist, poor, chalky sand, without covering it. After a cold winter it germinates in spring; the seedlings grow slowly and usually do not flower in their first year.

Division

A plant with several rosettes can be carefully divided in April, with a good ball of soil. It does not always work, because the plant dislikes disturbance.

Grass-of-Parnassus: how does it get through the winter?

Hardy to −30 °C.

• In autumn the leaves die back; the plant overwinters as a bud at ground level.
• Very hardy: it grows far into northern Europe and high in the mountains.
• A short-mown, open spot lets the light reach the ground quickly in spring, so the new rosettes get off to a good start.

Diseases and pests

• Drying out: In a dry summer it soon disappears. Choose a spot that always stays wet, such as a pond margin or a bog bed.
• Being overgrown: Tall grasses, reeds, rushes and young willows take away its light. Mow every year and pull out young woody growth in good time.
• Slugs and snails: They eat the young leaves and flower buds. In a wet spot with frogs, toads and ground beetles the damage usually stays limited.
• Too rich: Manure, compost or nutrient-rich water encourage algae and vigorous plants. Keep soil and water poor and do not use potting compost.

Through the year

• March: Scratch open a few small patches of bare soil for self-sown seedlings.
• April: New leaf rosettes. Plant or carefully divide.
• May: Plant. Keep the soil well wet.
• June: The flowering stems grow. Water in dry spells.
• July: First flowers. Do not mow.
• August: Full flower. Flies and hoverflies visit the flowers.
• September: Last flowers; the seeds ripen. Plant, or sow in pots.
• October: Mow and remove the cuttings.
• November: Sow in pots and leave them outside over winter.
• December: Dormant. The plant overwinters as a bud.

Did you know?

• The name refers to Mount Parnassus in Greece: the Greek physician Dioscorides described a ‘grass of Parnassus’, and the name has stuck to this plant.
• The glistening knobs on the fringed scales look like drops of nectar but give nothing: they are there to lure flies. The real nectar sits at the base of the scales.
• Grass-of-Parnassus used to be placed in the saxifrage family. DNA studies showed that it is related to spindle, and it is now placed in the spindle family.