Sea Holly

Sea Holly (Eryngium planum) is a spiky, architectural perennial about 50cm tall and wide, with silvery holly-like leaves and metallic blue flowerheads like small raspberries wrapped in a lacy ruff. They open in late spring and last through summer, then stand dried into autumn. It is cold hardy, drought tolerant and a magnet for pollinators.

Why you'll love it

• Blue that stands out. Metallic blue flowerheads are rare in the garden, and they look sharp beside silver foliage and soft grasses.
• Architectural shape. Open, branching, thistle-like stems and spiky leaves give a mixed border structure all season.
• Very cold hardy. It shrugs off hard frosts, so it works in cold districts where many perennials fail.
• Drought tolerant once mature. After the first season it copes with dry spells on very little water.
• Good for pollinators and cut flowers. Bees and butterflies visit the flowers, and the heads last well in a vase or dried.

Where it works best

Mixed borders and cottage gardens. Plant 50cm apart in drifts of three or five. The silver-blue colour pulls a border together and holds its shape long after other flowers have finished.

Prairie-style plantings. Set it among ornamental grasses, where its spiky texture contrasts with soft, flowing foliage.

Cut flowers and dried arrangements. Cut the flowerheads in summer for a vase, or leave them to dry on the stem and enjoy them into autumn.

Growing Sea Holly in Australia

Position and climate. Full sun is essential. It is very cold hardy, so it is at its best in cool temperate, Mediterranean and warm temperate gardens with a distinct cold season. Winter wet is its enemy: in wet-winter regions plant it on a raised mound. We would not choose it for the humid tropics or subtropics, where summer humidity and wet soil make it hard to keep.

Soil. Plant into free-draining soil. It will grow in moist soil, provided the ground dries out in winter. Poor, lean soil suits it better than rich ground, which makes it floppy.

Water and feed. Mulch and water regularly until the plant is established, usually around 12 weeks. After that it is drought tolerant. Feeding is rarely worthwhile.

Pruning. It is deciduous, so cut the dead stems back in late winter and let new growth start from the base. Leave the dried flowerheads standing through autumn if you like the look.

What to expect when it arrives

We sell Sea Holly as tube stock (a young plant in an 80mm deep tube that establishes quickly) and in 140mm pots in packs of 10. Tubes are the economical way to plant a border, and the 140mm pots give a more established clump. Expect a modest plant at first. It flowers better after it has been in the ground for a year or two, and it may look bare in winter because it is deciduous.

Plants are delivered Australia wide, with delivery from $29.95. Every plant is covered by our 30 day healthy plant guarantee.

Plant care guides and related reading

• Perennials for a cottage garden
• Plants for bees and butterflies
• Frost hardy plants
• Drought tolerant plants

Common questions

Why has my sea holly not flowered?

Plants flower better once they have been in place for a year or two, so be patient. Full sun and lean, free-draining soil also help.

Does it die back in winter?

Yes, it is deciduous. The stems die down in the cooler months, so cut them back in late winter and expect fresh growth in spring.

Will it grow in clay?

Only with care. It will grow in moist soil if the ground dries out in winter, but it hates winter wet around the roots, so raise the bed or add plenty of grit.