Sea holly brings extraordinary architectural beauty to the garden by day, and wonderment at night as it reflects the silvery moonlight. It blooms profusely through the summer, attracting pollinators and providing garden interest in winter with long-standing blooms. Cut flowers are captivating in fresh or dry arrangements. This tough plant thrives in poor soil, heat, and drought, and even tolerates salty soil as found in coastal areas. Perennial in USDA zones 5–9. Deer and rabbit resistant.
Botanical Name: Eryngium planum
Native: Europe and Asia
Hardiness: Perennial in USDA zones 5–9
Plant Dimensions: 24″–48″ tall
Variety Information: ½”–1″ flower heads made up of many tiny flowers start out green and turn to silvery-blue as the flowers open.
Exposure: Full sun
Bloom Period: Summer to frost
Attributes: Attracts Pollinators, Cut Flower, Drought Tolerant
When to Sow Outside: Sow in fall or late winter.
When to Start Inside: RECOMMENDED: 10 to 12 weeks before your average last frost date. Ideal soil temperature for germination is 70°–75°F.
Days to Emerge: 7–90 Days
Seed Depth: Press into surface
Seed Spacing: A group of 3 seeds every 18″–24″
Thinning: When 1″ tall, thin to one every 18″–24″
Special Care: For optimal germination, stratify sea holly seeds. Stratification is the process of subjecting seed to moist, cold treatment to break dormancy, which occurs naturally when seed is sown outdoors in fall. When starting seed indoors in spring, sow the seed into a container of moistened seed-starting mix, cover with clear plastic wrap, and leave the container in a refrigerator for 2 to 3 weeks, then move to a room temperature location to germinate. Keep soil evenly moist.
Harvesting: For longest vase life, harvest in the morning and change vase water frequently. For Drying: Harvest flowers when they are green; they will resist turning brown over time.