Blaukappe Sea Holly is a striking cultivar of Eryngium planum that brings architectural elegance to summer and fall gardens. Its steel-blue flower heads rise 24 to 30 inches tall on wiry stems, creating an almost otherworldly presence in the landscape. Hardy in zone 4, this plant thrives on neglect once established, asking only for full sun and well-draining soil. It blooms reliably from June through November, attracting pollinators throughout the season while resisting deer browsing and tolerating drought with ease.
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Full Sun
Low
4-4
30in H x 18in W
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Moderate
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The blue-tinged flowers appear in a form unlike most ornamentals, with metallic bracts surrounding delicate blooms that seem almost frozen in time. Blaukappe stands tough and reliable in cold climates, handling zone 4 winters without fuss while demanding virtually no supplemental water once rooted. Pollinators flock to its nectar-rich heads from early summer straight through the first hard frosts, making it both a visual anchor and an ecological asset in any garden.
Blaukappe Sea Holly serves primarily as an ornamental flower, valued for its distinctive blue flower heads and architectural form in border plantings, cottage gardens, and pollinator landscapes. Its long bloom window and tolerance for poor conditions make it particularly useful in low-maintenance mixed perennial borders where visual interest is needed through late fall.
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Surface sow seeds in pots 10 to 16 weeks before your last spring frost. Keep soil at 70 to 75 degrees Fahrenheit until germination occurs (expect 7 to 28 days), then drop to 55 to 60 degrees Fahrenheit. If no seedlings appear after four weeks, cover the pots with plastic and refrigerate for about four weeks, then return to warmth to trigger germination. Bottom water or mist regularly to avoid accidentally covering the seeds.
Harden off seedlings over 7 to 10 days by gradually exposing them to outdoor conditions. Transplant after your last frost date when soil has warmed. Space plants 18 inches apart and water in gently, then reduce watering once established.
Direct sow in fall or earliest spring, or use winter sowing by placing seeds in pots in the shade during winter months. Seeds need light to germinate, so do not cover them with soil.
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