Eryngium — 19 species

Eryngium, commonly called sea holly, is a genus of spiny-bracted perennials and biennials prized for their striking steel-blue or silver flower heads. Cultivars such as 'Blue Hobbit', 'Big Blue', 'Picos Blue', and the towering 'Silver Ghost' bring sculptural drama to borders from midsummer onward. They demand full sun — at least six hours daily — and thrive in poor, well-drained soils; established plants are highly drought-tolerant and rarely need supplemental watering. All species in this genus are toxic to cats and dogs, so plant them where pets cannot graze.