About
Eryngium planum, the flat sea holly, is an upright, clump-forming perennial to around 90 cm with oval, heart-shaped basal leaves and, in summer, freely branching stems carrying numerous small, rounded, steel-blue flowerheads surrounded by narrow, blue-grey bracts. One of the most reliable and free-flowering of all the blue-flowered sea hollies.
About the genus
Eryngium, the sea hollies, are biennials and perennials with spiny-margined, often architectural leaves and distinctive, dome-shaped flowerheads surrounded by spiny bracts, often in metallic shades of blue, silver or purple. Drought-tolerant and ornamental, they are grown in sunny, well-drained borders.
Plant details
Suggested usesBedding, containers, hanging baskets.
Care notes
CultivationPlant out after last frost in fertile, well-drained soil.
PruningDeadhead regularly to prolong flowering.
PropagationGrow from seed sown in spring.
Pest resistanceGenerally pest-free. Monitor for common garden pests.
Disease resistanceGenerally disease-resistant. Ensure good air circulation.