Eryngium alpinum aka Queen Of The Alps

Eryngium alpinum is a herbaceous perennial in the Apiaceae family. Its common names include alpine sea holly and alpine eryngo. It comes from central and southeastern Europe, including the Balkans. Wild plants grow in rocky subalpine sites and moist pastures. They occur at heights up to 6,500 feet [1,981 metres]. This species is not native to Britain or Ireland.

Plants form clumps with a basal rosette and deep taproot. Stiff, branched stems give the plant an upright shape. Garden plants reach about 2–3 feet [0.6–0.9 metres] tall. The RHS gives an upper height of 3.3 feet [1 metre]. Spread is about 1.5–2 feet [0.46–0.61 metres]. Basal leaves are heart-shaped, glossy, and dark green. The foliage dies back each year. Blue stems carry the flower heads above the leaves.

Each cone-shaped head holds many tiny blue to purple flowers. The heads reach about 0.17 feet [0.05 metres] long. A collar of finely cut blue bracts surrounds each head. These bracts look spiny, though Missouri Botanical Garden describes them as somewhat soft. Their blue colour is strongest with full sun and cool nights. Main flowering falls in July and August. Missouri Botanical Garden also describes blooms lasting into early October. The seedheads can remain as a feature through winter.

Give this plant full sun and soil that drains well. Poor to moderately fertile soil suits it well. It grows in chalk, loam, or sand across acid to alkaline conditions. It tolerates drought, dry soil, salt, and some light shade. Yet shade or rich, moist soil can make tall stems sprawl. Protect the crown from winter wet; gravel mulch may help. Its taproot makes moving established plants difficult. The RHS rates it H5, while Missouri Botanical Garden lists USDA zones 2–8. Plants take two to five years to reach full size.

Use alpine sea holly in borders, cottage gardens, or gravel beds. It also suits coastal sites and wildlife gardens. Plant it alone, in small groups, or in larger drifts. The flowers last well when cut and also dry well. Remove spent blooms for a tidier look, or keep the seedheads. Sow ripe seed in pots in a cold frame. Missouri Botanical Garden reports no major pest or disease problems. The RHS lists possible leaf and bud eelworms, slugs, and snails. Root rot and powdery mildew can also occur.