Soapwort

Soapwort: how do you recognise it?

Habit

Upright stems 40–60 cm tall that spread by runners into patches 60 cm wide and more.

Leaves

Lance-shaped to oval, 5–10 cm, smooth, in opposite pairs, with three distinct parallel veins.

Flower

Pale pink to white, about 2.5 cm across, with five petals on a long calyx tube, in dense clusters at the stem tips. Double in ‘Rosea Plena’ and ‘Alba Plena’.

Scent

Sweet and spicy, strongest in the evening.

Roots

Creeping, fleshy rhizomes that spread far underground.

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

Why grow it?

• Scented pink flowers from July to September, when many other native plants have finished.
• Attracts moths in the evening with its sweet scent, and bees and butterflies by day.
• Tough and easy on dry to normal soil, in sun or partial shade.
• Quickly fills a bare spot, a bank or a rough corner of the wildlife garden with its runners.
• The double forms are lovely old-fashioned border plants that stay attractive for a long time.

Soapwort: where does it grow best?

• Sun to partial shade; in sun it flowers more and stays sturdier.
• Sand, loam or clay, acid to chalky.
• Dry to normal soil; on rich, moist soil it grows more lushly but flops more easily.
• Give it a spot where it may spread, or plant it behind a root barrier.
• Plant 40–50 cm apart.

Light

Sun and partial shade

Soil type

Sand, loam or clay

Acidity

Not fussy

Moisture

Dry or normal

Size

0.6 m tall, 0.6 m wide

Hardiness

Hardy (to -30 °C)

Goes well with

• Evening primrose: Yellow flowers that open in the evening: together a garden for moths.
• Honeysuckle: A scented climber for a hedge or fence, also loved by moths.
• Common mallow: Purplish-pink flowers in the same summer, on the same dry soil.
• Wild marjoram: A low, pink bee plant for the front of the patch.

Soapwort: when and how to plant it?

Plant in March–May and September–October.

1. Plant from March to May or in September–October.
2. Choose a spot where it may spread, or sink a root barrier 20–30 cm deep.
3. Dig a hole slightly larger than the pot and set the plant at the same depth as in the pot.
4. Leave 40–50 cm between plants. No fertiliser or compost is needed.
5. Firm in and water well. In the first year water during long dry spells.
6. Wear gloves and wash your hands after planting.

Care

Water

Only in the first year during dry spells. After that it copes well with dry summers.

Feeding

Not needed. On rich soil it becomes floppy.

Support

In May, push a few twigs or a ring in around the patch, or plant it among sturdy neighbours.

Spent flowers

Cut off spent clusters for a longer display and fewer seedlings.

Runners

Every spring, cut off runners that grow outside the intended spot with a spade.

Tip: Plant it near a terrace or seat, so you can smell the scent and watch the moths in the evening. Give it a spot where it may spread; the double forms stay attractive the longest.

Soapwort: when to prune it?

Pruning months: March and August.

When: In August cut back after the first flush, and in late February–March clear the old stems.

How:

• In August, cut the spent stems back by a third: you get a second flush in September and a sturdier plant.
• In March, cut all old stems down to just above the ground.
• During the spring work, also cut off any runners that have gone too far.

Caution: Wear gloves when cutting back and keep the sap out of your eyes.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Division

In March–April or September–October: cut off a piece of the patch with rhizomes and shoots and replant it elsewhere at once.

Runners

In spring: dig up a runner with roots and plant it in a pot or a new spot. This is also how to propagate the double forms.

Cuttings

In May–June: take 8–10 cm cuttings from non-flowering shoots and root them in moist cutting compost.

Soapwort: how does it get through the winter?

Hardy to −30 °C.

• Fully hardy, to about −30 °C: no protection is needed in Belgium.
• The stems die back above ground; the rhizomes overwinter in the soil.
• Leave the old stems until March: they give insects shelter.

Diseases and pests

• Spreading: The runners pop up among other plants. Use a root barrier and cut them off every spring.
• Flopping: After rain or on rich soil the stems fall flat. Stake in May, do not feed and cut back in August.
• Slugs: Eat the young shoots in spring. Pick them off in the evening or spread a rough layer around the young shoots.
• Bare stems: In late summer the lower stems become bare and yellow. Put lower plants in front of the patch.

Through the year

• March: Cut off old stems. Plant, divide or cut off runners.
• April: Plant. Watch for slugs.
• May: Add support. Take cuttings.
• July: Flowering starts. Moths at the scented flowers in the evening.
• August: Cut spent stems back by a third.
• September: Second flush. Plant or divide.
• October: Plant. Leave the stems standing for winter.
• December: Rest. Leave the old stems standing.

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.

Butterflies

Nectar for butterflies.

Did you know?

• The roots and leaves contain saponins, which produce a gentle lather in water. Wool and fine fabrics were once washed with it, and conservators sometimes still use it for old textiles.
• The long calyx tube hides the nectar deep in the flower. Only insects with a long tongue, such as moths and hawk-moths, can reach it easily.
• Soapwort has been grown in gardens for centuries. The double forms are still often seen in old cottage gardens.