Steel Blue Sea Holly is a frost-hardy perennial that brings an otherworldly shimmer to sun-drenched gardens across hardiness zones 5 through 9. This cultivar of Eryngium planum grows 24 to 48 inches tall and produces distinctive steely blue flowers that attract pollinators while thriving in lean, well-draining soil where many ornamentals struggle. It demands full sun and low water once established, rewarding patient gardeners with a long season of architectural blooms and remarkable drought tolerance.
Full Sun
Low
5-9
48in H x ?in W
—
Moderate
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Steel blue flowers emerge on branching stems with a metallic sheen that catches the light beautifully, creating an almost ethereal effect in the garden. This plant grows happily in poor, sandy, or gravelly soil where other perennials would languish, and its deep taproot system makes it exceptionally drought-tolerant once established. The flowers persist for weeks, providing late-season interest and sustenance for beneficial insects when other blooms have faded.
Steel Blue Sea Holly serves primarily as an ornamental perennial, valued for its distinctive steel blue flowers that add striking color and texture to mixed borders, cottage gardens, and naturalized plantings. The flowers dry exceptionally well, making them excellent for dried arrangements and cut flower displays that retain their metallic blue tone for months.
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Start seeds indoors 10 to 12 weeks before your average last frost date in soil temperature of 70 to 75 degrees Fahrenheit. This extended indoor start allows seedlings to develop strong root systems before transplanting.
Transplant seedlings outdoors 10 to 12 weeks before your average last frost date once they've developed true leaves. Harden off gradually over 7 to 10 days before moving to permanent positions.
Sow seeds directly in fall or late winter, pressing them into the soil surface. Fall sowing takes advantage of natural cold stratification and winter moisture.
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