Eryngium (Sea Holly)

Few plants offer the electric, metallic intensity of Sea Holly. Eryngium planum produces a candelabra of branching stems, each tipped with a thimble-sized cone surrounded by a spiky silvery-blue ruff that turns a vivid, shimmering steel-blue in full summer sun — the stronger the light, the deeper and more metallic the colour becomes.

Ultra-hardy (H7), drought-tolerant, and providing hundreds of stems that last two weeks fresh or indefinitely when dried. Thrives in poor, lean soil — do not over-feed. Approximately 150 seeds per packet.

• Eryngium planum — Hardy Perennial (H7)
• Height: 90cm | Flowers: July–September
• Sow indoors February–April; may need cold stratification if slow
• Full sun; poor, sharply drained soil — hates waterlogging
• Do not move once established — deep taproot
• Outstanding for cutting fresh and drying

Grow it with Echinacea purpurea for a late-summer combination of steel-blue spikes and drooping pink petals that is one of the great pollinator borders.