Rock soapwort

Rock soapwort: how do you recognise it?

Habit

Low, cushion-forming to trailing perennial about 15 cm tall and 50 cm wide, with slender, sprawling stems.

Foliage

Small, oval and green, slightly hairy; set close along the stems.

Flower

Small pink five-petalled flowers in loose clusters, from May to July. White and deeper pink forms also exist.

Roots

Fine root system that needs free-draining soil and dislikes wet soil in winter.

Flowering: May–July · Plants: March–April and September · Pruning: July

Why grow it?

• A cloud of pink flowers from May to July, one of the best for the rock garden.
• Tumbles like a waterfall over walls, rocks and the edges of steps.
• Ground cover for full sun and dry, poor soil; drought-tolerant once established.
• The flowers attract bees.
• Very hardy (to −30 °C) and almost no maintenance.

Rock soapwort: where does it grow best?

• Full sun: the more light, the more compact the cushion and the richer the flowering.
• Sandy or loamy soil, neutral to chalky, poor and well-drained.
• Dry to moderately moist; it hates wet feet, especially in winter.
• Ideal at the top of a wall, in a rock garden or in a gravel bed; allow 40–50 cm per plant.

Light

Sun

Soil type

Sand or loam

Acidity

Neutral or chalky

Moisture

Dry

Size

0.15 m tall, 0.5 m wide

Hardiness

Hardy (to -30 °C)

Goes well with

• Creeping thyme: Low, fragrant ground cover for the same dry sun.
• Stonecrop: Sedum for rock gardens and walls; tolerates the same poor soil.
• Rock pink: Dianthus flowers at the same time, with scent and colour.
• Bellflower: Blue bells that contrast nicely with the pink.

Rock soapwort: when and how to plant it?

Plant in March–April and September.

1. Plant in March–April or in September, when the soil is not frozen or waterlogged.
2. Lighten heavy soil with coarse sand or grit so that water drains away well.
3. Set the plant at the same depth as in its pot, no deeper.
4. Leave 40–50 cm between plants and plant at the edge of a wall.
5. Water well after planting, then only in a prolonged dry spell.
6. Spread a layer of fine gravel around the plant rather than compost; this keeps the neck dry.

Care

Water

In the first year water a few times in dry weather; after that it is rarely needed.

Feeding

Almost unnecessary. Soil that is too rich gives soft growth and fewer flowers.

Mulching

Use fine gravel or stone chippings around the plant, not compost or leaves on the neck.

Cutting back

Cut back firmly after flowering: this keeps the cushion compact and dense.

Weeding

Weed between the plants in the first year; later the cushion closes up and weeds stay away.

Tip: Put it at the top of a wall or in a gravel bed. Cut back firmly straight after flowering and give it poor, well-drained soil.

Rock soapwort: when to prune it?

Pruning months: July.

When: Straight after flowering, in July.

How:

• Shorten all stems by a third to a half, above the green part.
• Remove dead or bare stems in March before the new shoots.
• Use sharp secateurs and clear away the clippings.

Caution: The plant sap is not for eating: wash your hands after pruning.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Cuttings

In July, after cutting back: take 5–8 cm cuttings of non-flowering shoots in sandy potting compost. They root in a few weeks.

Division

In March–April, carefully lift a piece with roots and replant it elsewhere.

Seed

In spring in a seed tray with sandy seed compost; it also self-seeds lightly.

Rock soapwort: how does it get through the winter?

Hardy to −30 °C.

• Very hardy, down to about −30 °C: no protection is needed in Belgian winters.
• The danger is wet soil, not frost: ensure good drainage and put grit around the plant.
• In a pot: stand it against a wall or on pot feet so that the pot does not fill with water.

Diseases and pests

• Rot from wet feet: The cushion yellows or dies in the middle. Mix grit or sand into the soil and choose a sunny spot.
• Bare, floppy stems: After flowering it becomes loose and bare. Cut back firmly.
• Slugs: Young plants are sometimes nibbled. Collect slugs in the evening and protect young plants.
• Weeds in the cushion: Weeds growing between the stems are hard to remove. Weed in the first year.

Through the year

• March: Plant. Cut away dead or bare stems.
• April: Plant. Spread gravel around the plant.
• May: Flowering begins.
• June: Full flower. Bees visit the flowers.
• July: After flowering, shorten by a third to a half. Take cuttings.
• August: Water young plants in dry weather.
• September: Plant. Pot on cuttings.
• October: Clear plant debris. Dormant.

Edible and useful

Not edible. Soapwort contains saponins, especially in the roots: whisked in water they lather like soap, and eating them causes a burning mouth, vomiting, stomach ache and diarrhoea. The root was once used to wash wool and fine fabrics; do not use it yourself as soap for your skin or face, and keep the lather out of your eyes. Children, dogs, cats and livestock such as horses and sheep are at risk: do not plant it in or beside a field, and do not throw dug-out pieces near the feed. Wash your hands after working with the plant. If any is swallowed, call a poison centre (in Belgium 070 245 245) or your doctor at once.

Good for wildlife

Bees

Nectar and pollen for honeybees and wild bees.

Did you know?

• The name Saponaria comes from the Latin sapo (soap): plants of this genus contain saponins, which foam in water.
• The species name ocymoides means ‘like basil’ (Ocimum), after the shape of the small leaves.