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Eryngium - Growing Guide
Growing Eryngium – Sea Holly
Care and thought is needed when considering the positioning of eryngium in your garden because different species come from different countries with markedly different growing conditions.
Those that originate from dry coastal areas of Europe, North Africa, Asia and China have tap roots, ovate to heart shaped and divided leaves and congested heads of blue or white flowers with conspicuous bracts.
Within this category come:
E. bourgatii – herbaceous perennial
E. alpinum – herbaceous perennial
E. giganteum ‘Mrs Willmott’s Ghost’ – herbaceous perennial
E. planum – evergreen perennial
E. x tripartitum – herbaceous perennial
E. variifolium – evergreen perennial
E. zabelii (E. alipinum x E. tripartitum) – semi evergreen perennial
These represent the majority of the species which we offer. They can readily be grown in well drained, poor to only moderately fertile soil in full sun with some protection from winter wet. A coastal setting is ideal where there are hot dry sunny banks.
There are however other species which come from Argentina, and elsewhere in South America, that originate in wet and marshy grassland. These have fibrous roots, evergreen sword shaped foliage and less showy greenish white flowers.
Within this category are:
E. agavifolium – evergreen perennial
E. padanifolium – evergreen perennial
These have rather different requirements. They need a moist, well drained and fertile soil in full sun. You might easily conclude that these are best grown in wetter areas of the country.
All eryngiums form basal rosettes, have leaves which are spiny with silvery white veins, and have crowded thistle-like umbels of stalk-less flowers on branched stems.
Eryngiums are some of the very best and most distinctive plants to grow in your herbaceous border. They hold their flowers for very long periods in the summer and they are fully frost hardy down to minus 10°C.
They spread and naturalise in the border and make wonderful dried flowers although they need to be cut for this purpose before the flowers are actually out. At Christmas they make wonderful decorations or show up well with cut winter flowers such as hellebores.
The secret to maintaining your plants in good order, as with many other herbaceous plants, is to remove the flowering stems after flowering is over and before a great deal of energy has been wasted in setting seeds. Although some to the plant are evergreen, and although the old flowering stalks retain colour long after flowering, they do need to be cut away from the plant well before they brown off, fall over, and begin to look unsightly.
Seeds can be sown in a cold frame in containers as soon as they are ripe. Clumps can be lifted and divided in the spring while still dormant. It can be a bit of a struggle to get the divisions re-growing and they can be slow to get away. Taking root cuttings from the clumps of these perennials in late winter is easier and may well give better results on bottom heat.
Images to follow