Petrorhagia saxifraga aka Tunic Flower

Petrorhagia saxifraga, or tunic flower, belongs to the pink family, Caryophyllaceae. Other names include coat flower and pink saxifrage. Its native range spans central and southern Europe to Iran. It grows in rocky, sandy soils, including lime-rich sites. This perennial has also spread beyond gardens in North America. It now grows in fields, meadows, and disturbed ground. Records include Quebec, Ontario, and the eastern and central United States.

The plant creeps outward to form a low leaf mat. Garden sources give heights of about 0.3–1 foot [0.1–0.3 metres]. The lower figure reflects its short carpet of leaves. Thin flower stems rise above this green base. Its spread can reach about 1.5–1.6 feet [0.46–0.5 metres]. Small, narrow, pointed leaves give the mat a grassy look. Leaves grow opposite one another on very thin stems. They stay green through winter where the climate is mild.

Small flowers have five petals and come in pink or white. Their fine stems give the flowering plant a loose, airy form. Missouri Botanical Garden lists bloom from May through August. Chicago Botanic Garden records flowers from May through October. The display suits rock gardens without hiding nearby stones. Cutting the plant back after flowering can prompt more blooms. Its low growth also suits path edges and border fronts. Stems can trail over walls, steps, and raised beds. Gardeners also use it as ground cover or on green roofs.

Give tunic flower full sun and soil that drains well. It grows in sand or loam and tolerates poor soil. Acid, neutral, and alkaline soils can all suit it. It prefers cool summers and tolerates drought once established. Yet its shallow roots can lose water fast. Mulch helps the soil hold moisture around those roots. Missouri Botanical Garden recommends moderate moisture for garden growth. The RHS rates it H4 for UK hardiness. US sources list USDA zones 5–7, with possible survival in zone 4. Plants take about two to five years to reach full size.

This plant needs little routine care and has few serious problems. Slugs and snails may still cause damage. The RHS reports that disease is seldom a concern. It can seed itself freely and spread strongly through gardens. Allow room for this habit when using it as ground cover. Sow seed in spring or autumn in pots with free-draining compost. Harden young plants off before planting outside after frost risk passes.