Eryngium offer interesting foliage and forms as well as flowers and stems in alluring shades of blue, violet and white, many with a metallic sheen. They range from British seaside native the sea holly, E. maritimum, to the statuesque South American species E. pandanifolium Award of Garden Merit (AGM), which can reach heights of 2.5m.
It is a huge genus of 230 species in the Apiaceae family. In cultivation a large group come from Europe and there are several South American species. All tend to have thistle-like flower heads surrounded by a ruff of spiky bracts. The leaves of the evergreen American species are long, sword-like and toothed, not unlike a bromeliad. The European species’ leaves are usually rounded or lobed. They can be either glossy green or bluey-green and often have attractive white veining.
Most of the European species are hardy to -15°C so can be planted in any area. The South American species, including E. agavifolium and E. pandanifolium AGM, can suffer below freezing. But they can do well given a sheltered corner with well-drained conditions.
Probably the best-known species is E. bourgatii from the Pyrenees. It has deeply divided leaves, marbled with white, and blue-green flowers. It is herbaceous so dies down in the winter. Related hybrid E. × zabelii is has some outstanding cultivars, including ‘Neptune’s Gold’.
But it is the American species that provide the wow factor by virtue of their height, silhouette and exotic look of their long, toothed leaves. I recently saw fantastic specimens of E. pandanifolium AGM at Arundel Castle. They provided structure to the borders as well being grown as standalone specimens, with highly attractive branched stems bearing numerous small flower heads.
Other great South American species include E. eburneum, which is perhaps the commonest of that region’s species found in our gardens, as well as E. agavifolium, E. yuccifolium and Christopher Lloyd’s favourite E. proteiflorum.
Some of the South American species, such as E. pandanifolium AGM, prefer moist soil. But generally Eryngium like a very well-drained soil. They can cope with poor gravelly soils that mimic the conditions of their natural habitat and they can tolerate lime. They like full sun. To avoid rot it is best to clear out dead foliage from around the crown before a cold wet winter sets in. Eryngium are a florist’s favourite and can be cut and hung upside down over winter to dry out before arranging.
What the specialists say
Neil Alcock, managing director, Seiont Nurseries, Gwynedd
"Eryngium are a valuable part of Seiont’s perennial production and sales, and are increasing year on year. This genus has a wide appeal to many sectors including retail and mail order, as well as landscapers and designers.
"E. × zabelii ‘Neptune’s Gold’ is a great variety, but then I’m bound to say that as I bred it. I also like E. × zabelii ‘Big Blue’. These two are our best-selling varieties. They partner well, attracting many beneficial insects. We also offer E. bourgatii ‘Picos Blue’ and ‘Picos Amethyst’.
"We grow Eryngium hard at Seiont, in a peat-free growing media, quite dry. They need the cold of winter to initiate more flowers for the following year."
Derry Watkins, owner, Special Plants, Wiltshire
"I adore Eryngium. They are handsome at all stages. My favourites are E. giganteum ‘Silver Ghost’, the E. × zabelii hybrids and E. pandanifolium ‘Physic Purple’. The latter variety blooms insanely late, in mid October. It’s 7ft tall with small, deep-red bobbles that turn brown and stand all winter, with a crazy eruption of long leaves at the base.
"The South American Eryngium are very different to European ones and have to be treated differently. They tend to have long, sword-like leaves, prefer a fairly moist soil and seed keeps for much longer than the Europeans. They will even tolerate some shade.
"For the European ones the tip is drainage, drainage and more drainage. E. giganteum is not so fussy though."
Rosy Hardy, owner, Hardy’s Cottage Garden Plants, Hampshire
"Eryngium is a very useful genus for a long summer season display in the herbaceous border and also a stalwart of the cut flower trade. Over the last few years the best variety we have sold is E. × zabelii ‘Jos Eijking’, followed by E. × zabelii ‘Big Blue’, although another top species for gardens is E. × oliverianum.
"They are a plant that likes to get that tap root down to find water. However, they don’t need to go into wet ground. The colour is always better if they are in a position in good sunlight. We would recommend
not to overfeed them as this has a detrimental effect."
Ian Garland, owner, Grangehill Landscapes, London
"I have used E. bourgatii and the related E. × zabelii ‘Big Blue’ many times. They provide a nice structure, low down towards the front or middle of a border. They do like it well drained though so I avoid areas that get boggy in the winter.
"I’ve heard great things about E. pandanifolium, which I’ve seen in a few high-profile gardens. I like their rosette of sword-shaped serrated leaves and the small teasel-like flowers on their branched stem that turn a chocolatey colour in autumn. They are not very hardy though so need a mild climate and shelter.
Apparently they need moisture-retentive soil but it also has to be well drained — that holy grail of soil is not always that easy to achieve."
Species and varieties
E. agavifolium is an evergreen perennial that produces branched stems bearing small pale-green flower heads in late summer above a rosette of sharply toothed sword-shaped leaves. Height: 1.5m.
E. bourgatii ‘Oxford Blue’ AGM (H5) is an erect herbaceous perennial with clumps of deeply divided basal leaves with silvery-white veins and cone-like, deep-blue flower heads surrounded by silvery-blue spiny bracts. Height: 40-60cm.
E. bourgatii ‘Picos Blue’ PBR is a larger and more intensely blue cultivar. Its leaves are grey-green with white veining. Height: 60cm.
E. giganteum AGM (H6), Miss Willmott’s ghost, is a robust biennial or short-lived perennial. Once it has flowered, it dies. It produces tall stems with spiny leaves and plenty of cone-like umbels of tiny blue flowers sitting within a rosette of spiny silvery-grey bracts. Height: 1m.
E. pandanifolium AGM (H4) produces a numerously branched stem bearing many small, round, purplish-grey flower heads that can mature to chocolate brown. It has a dense, basal rosette made up of large sword-shaped, spiny-margined blue-green leaves. Height: 1.5-2.5m.
E. pandanifolium ‘Physic Purple’
is an earlier-flowering form of the species that also has richer purple flowers. Originally found at Chelsea Physic Garden and it comes true from seed.
E. planum is a robust perennial that has a clump of rounded basal leaves and branched stems covered with deeply-lobed, blue-tinged, spiny leaves. Not a favourite of Christopher Lloyd, who said it has "little charisma", but it remains popular because of its sprays of pale-blue flower heads with narrow spiny bracts. Well used by florists. Height: 75-90cm.
E. yuccifolium is a very hardy evergreen perennial from central USA that produces a branching candelabrum of small, pale-green/white inflorescences in late summer above sword-shaped, spiny-edged, blue-grey leaves. Height: 1.2m.
E. × oliverianum AGM (H5) is an erect herbaceous perennial that has large blue flower heads surrounded by narrow metallic-blue bracts. Its heart-shaped leaves are distinctly toothed and it has a metallic violet-blue sheen on its stems when grown in full sun. Height: 60-90cm.
E. × tripartitum AGM (H5) is an herbaceous perennial with violet-blue stems bearing cone-like purple heads surrounded by narrow dark-blue bracts above a basal rosette of grey-green leaves. Height: 1m.
E. × zabelii ‘Big Blue’ is an upright herbaceous perennial with spiky, divided, silvery-green foliage. Stiff branched stems are topped with blue thimble-shaped flower heads surrounded by a ruff of prickly, silvery-blue bracts. Height: 75cm.
E. × zabelii ‘Neptune’s Gold’ is a fantastic variety selected at Seiont Nurseries. Electric blue flowers are surrounded by bracts that graduate from silver to gold. Best new perennial in UK Grower Awards 2015. Height: 60cm. Spread: 30cm.
Thank you to Floramedia, which supplied the images for this article from its photo library