Eryngium × zabelii 'Big Blue' (sea holly) brings dramatic, iridescent blue flower heads with spiny bracts to your garden in summer. You will get an upright, clumping perennial with bold texture for borders, gravel gardens, and cutting beds, plus excellent dried stems for arrangements.
Give it full sun for the strongest color and the sturdiest stems. Plant it in dry to average, well-drained soil - sandy or gravelly sites are ideal. Once established, it tolerates drought and heat far better than rich, moist conditions, which can cause sprawling growth. Water regularly the first season, then let the soil dry slightly between deep soakings.
Mature size is about 24-30 inches tall with a spread around 24-30 inches, making it easy to tuck into mixed plantings without crowding. Leave it undisturbed if possible, since sea hollies dislike frequent transplanting. A light spring cleanup and an optional late-season cutback after bloom are usually all it needs.
Pollinators will work the flowers when they are in peak color, and the spiny foliage helps it shrug off browsing in many landscapes. Pair it with other sun lovers and airy companions so the steel-blue tones stand out and the stems stay upright and neat.