Saponaria ocymoides aka Rock Soapwort

Saponaria ocymoides is known as rock soapwort or tumbling Ted. It belongs to the carnation family, Caryophyllaceae. This perennial grows on rocky mountain slopes in Europe. Its native range includes Spain and southwestern and south-central Europe. It grows on sunny rocks, often over limestone. People have introduced it to Britain, Scandinavia, and parts of America.

The plant forms a low mat with many branches. Its stems mound up, then trail across the ground. Garden plants reach about 0.5–0.75 feet [0.15–0.23 metres] tall. They spread about 1–2 feet [0.30–0.61 metres] wide. RHS gives a lower height, under 0.33 feet [0.10 metres]. Growth is moderate, with maturity reached in two to five years. The red stems can become partly woody. Fine hairs cover both stems and leaves. The grey-green leaves grow in opposite pairs, close to the stems. They have smooth edges and oval to lance-shaped outlines. The foliage can stay green through part of winter.

Loose clusters of pink flowers cover the mat during bloom. Some flowers have a purple tint. Each flower has five petals and a round outline. Flowers measure about half an inch to an inch across. The listed flowering season runs from May to August. A flush of flowers may last about three weeks. The fruit is a capsule. The plant can seed itself without becoming aggressive.

Grow rock soapwort in full sun and soil that drains well. It suits loam or sand with neutral to alkaline pH. Dry to moist soil suits it, but avoid waterlogged roots. Established plants withstand some drought. Sources place it in USDA zones 2–9 and RHS class H5. Hot, humid summers and wet winter roots can cause trouble. Cut plants back after bloom to keep their shape compact. This can also prompt branching and another flush of flowers. Divide clumps in spring or summer. Seeds and softwood cuttings offer other ways to grow new plants.

Use it along borders, in rock gardens, or in pots. Its trailing stems can hang over walls and container rims. It also fits between stepping stones, away from heavy foot traffic. Deer resistance adds value where browsing causes damage. Few diseases trouble it, though slugs and snails may feed on it. No edible or medicinal uses are known. It contains saponins, which can be toxic when swallowed. All parts can supply a soap substitute when simmered in water.