Sea hollies (Eryngium) have spiky leaves and thistle-like flowers in colours ranging from grey to intense cobalt blue, surrounded by a characteristic ‘ruff’. They make striking garden plants and have excellent wildlife value, particularly for pollinators. There are over 250 species of Eryngium, including plenty of cultivated varieties. As their name suggests, they grow well in coastal areas. They look wonderful in gravel gardens or mixed herbaceous borders.
Eryngiums make good winter silhouettes in the garden and the flowerheads work well in both fresh and dried arrangements. To dry sea holly flowers, simply cut them at the base of the plant and hang them upside down in a dry spot such as a shed or a garage.
How to grow sea holly
Grow sea hollies in full sun in free-draining soil, ideally where the soil stays relatively dry in winter. Protect the roots with a straw mulch in winter. Cut back the flower spikes in spring.
Where to grow eryngiums
Eryngiums need plenty of sunshine and free-draining soil. They can tolerate poor soil, and a spot at the foot of a wall is a good position as the soil will remain dry over winter. It’s also a good idea to plant eryngiums away from the edge of a border or path, as their spikes can be quite sharp. They work well in gravel gardens and don’t need a lot of watering.
How to plant eryngiums
Dig a generous hole, larger than the pot your sea holly came in and add a handful of grit to boost drainage. Follow our step by step guide to planting perennials.
Caring for eryngiums
In colder climates you may need to protect the roots with a mulch of straw over winter, and tidy spent foliage in spring to prevent rot.
Propagating eryngiums
Species eryngiums can be grown from seed, although if you have a named cultivar, take root cuttings to ensure it stays true to type. Follow our step-by-step guide to taking root cuttings. Some eryngiums can be propagated by division in spring. Watch Sarah Raven demonstrate how to divide herbaceous perennials.
Eryngiums: problem solving
Eryngiums are generally trouble-free plants with no pests or diseases, though slugs and snails can slowly eat small parts of the tough foliage.
Advice on buying eryngiums
- There’s a huge variety of cultivated seal hollies to choose from, with varying colours and heights. Make sure you choose the right one for the space you have in mind
- Most garden centres and online retailers will have some eryngiums for sale but specialist nurseries will have the greatest range of plants
- Always check plants for signs of pests and diseases before buying
Where to buy eryngiums online
Eryngiums to grow
- Eryngium varifolium – a compact sea holly, with small spiky flowers on sturdy, upright stems from July to September
- ‘Neptune’s Gold’ – a colourful plant. The spiky bracts are silvery blue at the base, turning gold at the tips. The stems of ‘Neptune’s Gold’ are blue, and the foliage yellow
- ‘Big Blue’ – as the name suggests, the flower cones are large and a very intense blue. They appear from June to August and contrast beautifully with the grey-green in leaves
- ‘Picos Blue’ – a more intense blue than the species bourgatii, and slightly larger
- Eryngium x tripartitum – with branching violet stems emerging from a rosette of leaves, the flowers are smaller and appear more starry, as the dark blue bracts are more like narrow daisy petals rather than lacy ruffs
