Sea holly varieties: the most beautiful at a glance
Sea holly species are often hardy, beautiful and also very useful for insects. Their thistle-like flowerheads look great in flower arrangements.
The frequently bizarre-looking flowering perennials have a lot to offer – be it bright blue flowers or agave-like leaves, we have compiled the most beautiful and fascinating species and their varieties. Check out our overview for everything you need to know about planting and caring for sea holly.
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Sea holly varieties and species: how many are there?
The genus Eryngium is the most diverse family of the umbellifer (Apiaceae) with about 230 known species. On almost every continent you can find a native species of sea holly – even in Europe wild growing specimens can be found.
The most beautiful species and varieties at a glance
Blue eryngo (Eryngium planum)
The deciduous flat-leaved blue eryngo even occurs in the wild from Central Europe to the Western Himalayas. The blue flowerheads appear from the end of June to mid-August and are surrounded by grey-blue bracts. This species grows up to 100cm tall and forms slender, upright clumps. It develops comparatively small flowerheads and bracts. Once a sunny site with well-drained soil has been found, Eryngium planum needs little attention from the gardener. This species successfully self-seeds and does not require a cold period for germination in autumn or spring.
Winter hardiness: down to -28 °C
- ‘Blue hobbit’: grows between 30 and 50cm tall and has intense blue coloured flowers. This variety grows well in small groups of up to 10 plants.
- ‘Blue cap’: flowers in an almost brilliant blue and should be planted in small groups with 9 other specimens, spaced 50cm apart.
Alpine eryngo (Eryngium alpinum)
As the name suggests, this species of sea holly is found in the Alps, with the northernmost occurrence in Switzerland, south of Lake Constance. The species prefers a moderate to good nitrogen supply. The thistle-like sea holly grows up to 60cm high and flowers intensely blue from July to August. In its natural habitat, alpine eryngo is unfortunately threatened with extinction. Although it is a beautiful perennial, it is not recommended for every location – it should be sunny and cool – a combination that is not often found in the garden. Eryngium alpinum rarely self-seeds and must therefore be sown selectively if necessary.
Winter hardiness: to -24 °C
- ‘Blue Star’: grows somewhat taller and reaches up to 80cm.
Miss Willmott’s ghost (Eryngium giganteum)
Miss Willmott’s ghost originates in the Caucasus, Turkey and Iran. In Europe, this species is currently becoming established as a neophyte. It tolerates partial shade very well and grows in its natural habitat on calcareous gravel soils, which is why this variety is suitable for rock gardens. Miss Willmott’s ghost is a biennial species and displays silvery bracts and white flowers at a maximum height of 70cm. The flowering period extends from the beginning of June to the end of July. Miss Willmott’s ghost germinates less easily on its own and therefore needs the gardener’s support.
Winter hardiness: to -24 °C
- ‘Silver Ghost’: is somewhat longer-lived than the pure species and forms narrower bracts.
Mediterranean sea holly (Eryngium bourgatii)
Eryngium bourgatii is native to the Mediterranean and Asia Minor and reaches a manageable height of 40cm. This species is comparatively long-lived and is suitable for dry and warm locations. If it is given enough sun, the bracts and stems turn a delicate blue. Like all sea holly varieties, this one does not tolerate compacted soil that tends to be waterlogged. Mediterranean sea holly propagates quite well by seed and by root cuttings.
Winter hardiness: to -24 °C
Agave-leaved sea holly (Eryngium agavifolium)
This species is a wintergreen perennial that is mainly characterised by its fleshy, slightly succulent leaves. Thorns on the leaf edge are also reminiscent of agave plants, which give this sea holly variety its name. In mild regions, Eryngium agavifolium can overwinter well; that said, even temperatures of -12 °C can cause leaf damage. This species is therefore wonderfully suitable for planting in tubs and it should definitely be protected in winter and at best wrapped with a fleece. Agave-leaved sea holly is quite successful at self-seeding and produces its green-white flowers in July – a total height of up to 120 cm is reached.
Winter hardiness: to -12 °C
Rattlesnake-master (Eryngium yuccifolium)
The delicate rattlesnake-master forms spherical, white-grey flower umbels at the beginning of July. The leaves are reminiscent of the genus Yucca, which is the reason for its Latin name. However, the species, which is easy to care for, is relatively lazy about flowering and enriches the garden every 2 years with its beautiful flower umbels. Their bracts remain small and have little effect on the ornamental value. Pay particular attention to a sunny location for this sea holly variety – it does not tolerate shade well.
Winter hardiness: to -12 °C
Field eryngo (Eryngium campestre)
Field eryngo is seen less in the gardens, but this species is still worth mentioning because of its bizarre structure. Altogether it reaches a height of up to 80cm, but forms strongly branched flower shoots, which is why it has a bushy growth habit. Eryngium campestre is competitive, develops taproots up to 180cm long and is thus extremely drought tolerant. A few spherical flower umbels appear from June to September. The seeds of field eryngo germinate very unevenly, sometimes over several months.
Winter hardiness: to -24 °C
Eryngium x zabelii
Eryngium x zabelii is a natural hybrid of Eryngium alpinum and Eryngium bourgatii and has the typical steel-blue bracts and flower umbels. Overall, it reaches a growth height of up to 70cm and can be planted in small groups with a maximum of 9 other plants. The hybrid is sterile and therefore does not self-seed. The flowering period extends from July to August.
Winter hardiness: to -24 °C
