Eryngium planum. This drought tolerant perennial thrives in sandy, well drained soil. Its stiff, spiny leaves are bluish green with silvery veins. It forms a clump over time, and blooms from June to September. The blue and white flower clusters each have a distinctive bract. Direct sow the seeds in autumn, or stratify in the fridge for three weeks if sowing in the spring. This involves planting into moist soil and enclosing the container in a plastic bag in the fridge. When the three weeks are up, move the bagged container into a warm room and await germination. Either way, this simulation of winter improves germination in Sea Holly seeds.
Known as Sea Holly as it thrives in the sandy, well drained soil near seashores. The seeds of Eryingium can be tricky to germinate, but if you follow our How to Grow Eryngium instructions, you should have good success.
Good drainage is fundamental to growing this plant.
Exposure: Full sun
Zone: Hardy to Zone 5
Germination can be slow, and the seeds benefit from vernalization. Sow pre-moistened flats and seal them in plastic bags in late. Refrigerate for two to three weeks. Then move the flats outdoors to a shady location after all threat of frost has passed. Transplant as seedlings appear, which usually takes two to three weeks. Or, more simply, direct sow in the fall.
Sow seeds 2mm (1/8″) deep. Germination can take 5 to 90 days, so be patient.
Water only during very dry spells. Carefully mulch around the crowns with fine gravel to keep plants dry over winter. The long taproots make transplanting difficult.