Soapwort: Planting, Growing and Caring

Botany

Soapwort (Saponaria) is a genus of perennial or annual plants with deciduous foliage, belonging to the Caryophyllaceae family, which also includes pinks (Dianthus), baby’s breath (Gypsophila), and Lychnis. Native to meadows and mountainous regions of southern Europe and western Asia, soapwort grows naturally in ditches, along riverbanks, on roadside banks, field edges, and wastelands. It is highly vigorous and quickly spreads via its running rootstocks.

Saponaria derives from the Medieval Latin “Sapo-ponis,” meaning “soap.” Indeed, soapwort has been known since antiquity for its cleansing properties. Hippocrates recommended using soapwort as a laundry detergent. The rootstocks, and to a lesser extent, the leaves and flowers of this herbaceous plant contain saponin, a natural surfactant that gives it foaming, degreasing, and cleansing properties. Laundresses used it to whiten linen by simply steeping the roots in boiling water. This unique characteristic earned soapwort names like “soap plant,” “fuller’s herb,” or “hedge pink.”

Soapwort is also renowned for its medicinal properties: it was used in leprosariums to clean wounds. This plant is effective in relieving skin conditions and clearing respiratory passages as an expectorant.

The Saponaria genus includes around twenty species, some of which are very easy to grow and exceptionally beautiful for adding a rustic, pastoral charm to borders, rockeries, or slopes. Saponaria officinalis is the wild species found in our countryside. It spreads rapidly via underground stolons and thrives in partially shaded or shaded areas, such as woodland edges. Its pale pink flowers bloom throughout summer. Horticultural varieties like ‘Alba Plena’ extend the colour palette to white.

Among perennial species, Saponaria ocymoides, the rock soapwort, forms dense flowering cushions perfect for covering rockeries, slopes, wall crevices, or even paving. It also thrives in containers on balconies and terraces, available in various shades of pink.

Like rock soapwort, Saponaria caespitosa and Saponaria pumilio are dwarf mat-forming varieties with dense foliage. Saponaria x olivana, a cross between the two, is prized for its ground-covering habit in rockeries, featuring small pink flowers with purple throats. Meanwhile, Saponaria x lembergii, a hybrid of S. officinalis and S. ocymoides, is highly floriferous and spreading. Saponaria calabrica, native to Calabria, is grown as an annual in temperate climates.

Depending on the species and variety, soapwort can form an upright clump 60–80 cm tall or a dense mat 5–20 cm high, spreading 40–60 cm wide.

Upright common soapwort and spreading rock soapwort

Soapwort has opposite, ovate or lanceolate, pointed leaves. They feel rough to the touch and are bright green. Deciduous along the stems, they are erect and sturdy in S. officinalis, while prostrate and spreading in S. ocymoides, slightly hairy, and also disappearing in winter. However, rosette leaves are more persistent.

Flowers and roots of Saponaria caespitosa, a mat-forming soapwort

From early summer until September (depending on the region), soapwort produces inflorescences in compact terminal cymes at the leaf axils. The short-petioled flowers have five unevenly spaced petals. S. officinalis flowers emit a clove-like scent, noticeable only at dusk. Other varieties are scentless. The flowers develop into ovoid or oblong capsules containing seeds.

Hardy beyond -20°C, soapwort is exceptionally easy to grow. Though unassuming, it is charming when planted in groups.

Some interesting soapwort varieties

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[product sku=”810092″ blog_description=”This soapwort forms a lovely flowering cushion in varying shades of vibrant pink. The ovate leaves are villous. Perfect for covering a rock garden or slope, or filling gaps in a dry stone wall” template=”listing1″ /]

[product sku=”81010″ blog_description=”This variety of soapwort offers semi-double, pure white pompon flowers with a light fragrance. It forms a lush, bushy clump” template=”listing1″ /]

[product sku=”8477″ blog_description=”This variety of soapwort produces semi-double flowers in a fairly rich pink from May to September” template=”listing1″ /]

[product sku=”P-11214-3209″ blog_description=”This horticultural variety of soapwort forms a very dense carpet of small ovate leaves and soft pink flowers. It thrives in rock gardens or in containers on patios and balconies” template=”listing1″ /]

How, when and where to plant soapwort?

Depending on the species of soapwort, the planting conditions vary slightly.

Where to plant it?

Generally, soapwort thrives in sunny locations. In southern France, partial shade will suit it better. However, full shade will completely halt its flowering.

In terms of soil, the different soapwort species have slightly different needs. Indeed, common soapwort, which grows naturally along our pathways, prefers humus-bearing, fairly fresh, light, and moderately fertile soils that must be perfectly drained. The more compact, spreading species prefer poor, even chalky soils, rather dry in summer, and not too rich. But this soil must also be very well-drained. This is why these species are perfect for rockeries, sunny slopes, and walls. You can even grow these species in pots or large containers on a balcony or terrace.

When to plant it?

As soapwort is a perennial plant, it is planted in spring, in March or April, or in autumn, in September-October. For spring planting, be sure to water it during the summer.

How to plant it?

Soapworts are planted in groups of 3 to 4 plants per square metre.

• Loosen the soil deeply
• Remove weeds and stones
• Add some organic amendments to heavy, clay soils, or a little compost or manure to poor soils for common soapwort. Ground-covering soapwort species need nothing
• Soak the root ball in a basin of water
• Dig holes twice the size of the root ball, spaced at least 30 to 40 cm apart
• Place the soapworts and fill the holes with the excavated soil
• Water generously and mulch.

Montpellier soapworts (Saponaria ocymoides) can be planted in pots, with drainage holes and clay pebbles, in a light substrate such as special Mediterranean plant compost.

How to pair soapwort?

The different varieties of soapwort will thrive in large borders of cottage-style gardens where their wildflower-like appearance will create a sensation, planted in groups of several young plants. Their wild nature allows them to pair beautifully with sturdy perennials such as artemisias, cornflowers, coneflowers, bee balms, sea hollies, spike speedwells (Veronica spicata), or garden phlox with very similar flowers… You can also add a touch of lightness with ornamental grasses like fountain grasses with their feathery spikes or Calamagrostis acutiflora ‘Karl Foerster’.

Around the soapwort, bee balms, sea hollies, speedwells, and garden phlox

On the other hand, varieties of Montpellier soapwort, planted on walls, slopes, or sunny rockeries, will thrive alongside sedums, houseleeks, or catchflies. They can also be planted at the base of roses or with snow-in-summer (Cerastium tomentosum) beneath shrubs and tall perennials.

The care of soapwort

Soapwort is a very easy-to-grow perennial that requires minimal maintenance. During the first summer, watering should be fairly regular (once a week), especially for common soapwort to keep the soil moist. Once established, watering can be spaced out as the plant should manage on its own, except during extreme heat or drought.

To encourage flowering and stimulate new blooms, don’t hesitate to deadhead spent flowers from common soapwort.

Flowers of common soapwort and Montpellier soapwort

At the very end of the flowering season, cut the plant back to ground level to prevent self-seeding and potential invasiveness. In winter, the deciduous foliage of soapwort almost entirely disappears, only to regrow vigorously in March-April.

Diseases and Pests of Soapwort

Soapwort is known for its excellent resistance with no known diseases or pests. Only slugs and snails may attack young shoots in spring. Ingrid shares 7 effective and natural ways to control slugs and snails.

The propagation of soapwort

Soapwort can be propagated by division or by sowing. Division should be done every 3 years, preferably in early spring. Sowing is also done in spring (April-May), or possibly in very early autumn, in August-September.

Division

• Dig up the clump with a garden fork
• Divide the clump by hand, separating it into several pieces, each with rootstocks and shoots
• Replant immediately

When dividing, don’t hesitate to take some roots to make a completely natural homemade laundry liquid. Simply wash the roots thoroughly to remove the soil. Then soak 70g of roots in a litre of water overnight. In the morning, boil for 15 minutes and strain. This laundry liquid keeps for two weeks.

Sowing

Sowing directly in the ground is done in April or May, once the soil temperature has reached 15°C.

• Work the soil well to loosen it
• Rake to remove weed residues and stones
• Flatten the soil with the back of the rake
• Sow the soapwort seeds broadcast
• Cover with a very thin layer of compost
• Water with a fine spray

Keep the soil moist by watering with a very fine spray until germination. Then it’s time to thin out, keeping only one seedling every 30 to 40 cm. When the soapwort young plants reach 15 cm, pinch them to encourage ramification.