Eryngium (Sea Holly) Seeds

Eryngium planum, known as Flat Sea Holly, is a robust Hardy Perennial (H7). Native to the dry plains of Eastern Europe, it is built for endurance, surviving temperatures down to -20°C and thriving in poor, sandy soils where other perennials might struggle to stay hydrated.

The "Blueing" Effect: While the stems and buds emerge green, they undergo a spectacular transformation as the UV intensity of the summer sun increases. The plant develops a metallic steel-blue pigment across its upper stems and ruffs—the stronger the light, the deeper and more shimmering the blue becomes.

The Taproot System: Sea Holly develops a long, vertical taproot that anchors it deeply into the soil. This allows it to access moisture far below the surface, making it exceptionally drought-tolerant. However, this also means it deeply dislikes being moved once established, so choose its permanent garden home carefully.

Eryngium can be slow to germinate but becomes incredibly self-sufficient once established in the garden.

How to Sow:
Sow indoors from February to April. Surface sow the seeds onto moist, gritty compost and cover with only a very fine dusting of vermiculite. If germination hasn't occurred after 3 weeks at 20°C, the seeds may require a "cold spell"—move the tray to a refrigerator (approx. 4°C) for 2-3 weeks before returning them to the warmth to trigger growth.

Where to Plant:
They demand full sun to develop their signature metallic colour. Sharp drainage is critical; the only condition that typically kills Sea Holly in the UK is waterlogged soil over winter. If your garden has heavy clay, we recommend digging in a significant amount of horticultural grit or planting into a raised gravel bed.

Ongoing Care:
Sea Holly actually performs better in lean, poor soil. Avoid overfeeding with high-nitrogen fertilizers, as this will lead to floppy stems and a loss of that prized metallic blue pigment. For drying, harvest the stems in late summer once the cones are fully coloured and the structure feels rigid and dry to the touch.

Because Sea Holly is so spiky and architectural, it looks best when softened by contrasting shapes or airy partners from our collection:

• 🌸 Echinacea purpurea: The Soft Contrast. The drooping, velvety pink petals of the Coneflower provide the perfect antidote to the rigid, steel-blue spikes of the Sea Holly. Together, they create a quintessential late-summer display that is a haven for butterflies.
• 💜 Verbena bonariensis: The Colour Echo. The electric blue of the Eryngium and the vibrant violet of the Verbena are perfect tonal partners. Both plants possess a "see-through" quality, creating a misty haze of blue and purple that adds depth to the back of a sunny border.

Sow indoors in spring for a shimmering candelabra of metallic blue from mid-summer until early autumn.