Ivory Sea Holly - Eryngium eburneum

by Martin Blow, SpecialPerennials

Eryngiums are well suited to our garden; they like free draining soil and don’t mind lots of water as long as it doesn’t stay around. In fact, this dry year (2022) has sorted the men from the boys when it comes to drought tolerance.

Over the years we’ve tried quite a few species and varieties with mixed success; some romp away and become architectural stars of the garden; others have failed to make it through the winter. This year some have struggled with the drought.

The blue flowered E.zabelli and E.bourgatii have both lost their leaves and gone dormant this summer. They do recover in the autumn.

Eryngium agavifolium is somewhat desiccated and awaits rains to “reinflate”.

One species, however, has shrugged off drought and decided the show must go on!

The star of our front garden is Eryngium eburneum, lacking a real common name, the epithet, eburneum, means “like ivory”, describing the flowers and flower stems so it is known as Ivory Sea Holly.

The narrow, spine-edged leaves can be 12-15” / 30-37cm long and the rosettes cover around 2ft 6in / 75cm after 3 years or so.

Our specimen, now 18 years old, is 4ft / 120cm across. The dark green leaves remain on the plant through the winter, except in the most extremes of temperatures; minus 15C killed the top growth but not the rootstock.

The plants have proved to be extremely drought tolerant requiring no watering and with no browning leaves by the end of August. In the autumn, some of the older leaves will start to die and these can be pulled off in late winter. The spines, although soft, can irritate with prolonged contact, so long sleeves and gloves are in order for this task.

Flowering starts in mid to late June. The emerging flower stems are green as first with the branching stems becoming more ivory coloured as they reach their ultimate height of 4-5ft / 120-150cm.

The flowers are white at first, then ivory, then greenish.

Bees, butterflies, and hoverflies throng to the flowers.

Flowering continues well into the autumn when the stems and seed heads turn brown. The dead stems create wonderful silhouettes through the winter and catch a dusting of frost and a tracery of spider’s webs.

The large, mounded rosettes of spiny leaves create a secure, warm, and dry winter home for our garden’s hedgehog.

Like most Eryngiums, eburneum can be propagated by division (least successful), root cuttings (most inconvenient!) and seed (easy once you know how). We leave the seed heads on the plants until late winter when we cut them and dry them in our greenhouse. We sow 4 or 5 seeds into each module in early spring using multipurpose compost or John Innes seed compost (a trial of peat free seed compost produced miserable results this year). The trays are left outdoors. Germination is usually very good. Once they have grown to about the width of the module across, we pot on the whole module into 9cm pots and grow on and they are usually of a reasonable planting size by July.

Eryngium eburneum comes from SE Brazil and NE Argentina, a sub-tropical area. It is also known as Eryngium paniculatum.

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