Of all the perennials in my garden, the large clumps of metallic blue eryngiums really do have the WOW factor. They are attractive nine months of the year from the emergence of the basal leaves in March followed by the young flowers which are greeny-silver in May/June and which begin to turn metallic blue or silver from July onwards. This colour is retained until September/October and even longer when cut and dried. Hot dry conditions seem to intensify the colour but some selected forms are better than others.
The ones I grow are E. giganteum, E. planum, E. bourgatii, E. x tripartitum and E. x zabelii. As with all members of this family, which includes astrantias, the flower is a collection of small flowers surrounded by a fringe of bracts. The size of the inflorescence, the length of the bracts and their spikiness and the shape of the leaves are all diagnostic features.
Eryngium giganteum is a biennial commonly known as 'Miss Willmott's Ghost'. It is easily grown from seed, the best form being Eryngium giganteum 'Silver Ghost'. At three feet tall it is a very architectural plant.
E. bourgatii. This species has distinctive white marbling on the dark green basal leaves. A good clump can be two feet tall. The flowers are slightly larger than E. planum and the bracts are broader. The selected form E. bourgatii 'Picos Blue' and E. bourgatii Graham Stuart Thomass Selection give the best colour. E. variifolium also has spiky marbled foliage but is a much smaller plant. It is readily available, looks good in a pot but not too impressive in the garden. One for the rockery perhaps.
E. planum has large, oval, soft, grey-green leaves and sprays of small flowers with linear spiky bracts. It is three feet tall and may need staking. This is the one used in bouquets. Two years ago I purchased E 'Jade' which was variegated. It has now reverted, but the intensity of the violet blue colour throughout the stems and flowers is amazing. It seems to be a form of E. planum but so far is only two feet tall.
My best plants are E. x tripartitum and E. x zabelii. Both are sterile hybrids and therefore only propagated from root cuttings.
E. x tripartitum is a very variable hybrid with a distinctive three lobed leaf up to five inches in length. My plant has reddish stems when the flowers are silver green. Then the plant goes violet blue as the season develops. It reaches three feet in height and can need staking.
E. x zabelii is a hybrid of E. alpinum and E. bourgatii and is also variable as you might expect. My plant has large flowers (same size as E. alpinum) but with spiky bracts. The foliage like E. bourgatii has silver marbled three lobed leaves and the colour is a wonderful metallic blue.
E. alpinum is one of the best eryngiums with large flowers that have soft bracts making it very touchy-feely unlike all the others. E. x oliverianum (an AGM plant) and a hybrid of E. alpinum and E. giganteum is also a very desirable plant. These last two are still on my must-have list.
The eryngiums are excellent bee plants and are performing well in the current hot dry conditions as they have deep tap roots.
First published in the South Pennine Group Newsletter, Autumn 2011
and subsequently in Cornucopia Issue 30.
© Copyright for this article: Janet Gears
This article was taken from a copy of Cornucopia that was published in 2012. You could be reading these articles as they are published to a national audience, by subscribing to Cornucopia.