A family of annuals, biennials and border perennials with architecturally pleasing foliage, stems and flowers. A traditional seaside garden favourite.
Family: Apiaceae (umbellifers)
Botanical Name: Eryngium
Common Names: eryngo, sea holly
Foliage: Deciduous or evergreen, simple or divided, dark green or blue-grey leaves, often spiny.
Flowers: Metallic, blue-grey or purplish, thistle-like, flower-heads, usually surrounded by spiny bracts.
Flowering Period: July-September.
Soil: Well-drained, poor to moderately fertile soil (chalk, sand or loam). Any pH.
Conditions: Best in full sun, will tollerate some shade. Plant in a east, west or south facing aspect.
Habit: Erect, clump forming.
Type: Herbaceous perennial.
Origin: Europe, North Africa, and North and South America
Hardiness: Most varieties are fully hardy in the UK.
A useful perennial for its ability to cope with hot, dry conditions and windy coastal locations.
It thrives in full sun and poor sandy soils. Deep-rooted, wind resistant and drought tolerant once established.
Plant out between autumn and spring in an open sunny spot, in a light, well-drained soil.
Ideal for flower beds or middle of the border.
Excellent for cutting and dried-flower arrangements.
Support tall varieties with twiggy sticks. Avoid waterlogged conditions and protect from winter wet.
The seed heads can be left-on overwinter for architectural interest. Cut the plants down to ground level in early spring.
Generally pest and disease free but can be affected by eelworms. Powdery mildews and root rot can be a problem in wet soil conditions.
Sow seed under glass when ripe or in early spring. Alternatively increase from root cuttings in midwinter or strike cuttings in spring using a propagator.
Large mature clumps can be divided but Eryngium dislikes root disturbance, which can temporarily affect flowering.
A number of good garden varieties are available, including:
Eryngium Agavifolium an unusual form that resembles a small agave, with a shiny bright green rosette of sword-like leaves, above which appear branched stems of bracted blossoms in shades of sage-green. Available from Gardening Express.
Eryngium alpinum (Europe) has heart-shaped basal leaves, deeply cut leaves and blue branching stems. Large cone-shaped blue flower heads, surrounded by spiky bracts, in july-August. Height to 2.5 ft (75cm). Available from Thompson & Morgan.
Eryngium bourgatii is a dwarf form with silvery blue leaves and strong stems of dark steel-blue flowers. Available from Gardening Express. Good cultivars include 'Picos Blue'.
Eryngium giganteum is a biennial with upright, branching pale grey stems and rounded, spiny leaves. Large ivory-blue flower-heads and bracts in July-August. Seeds itself freely. Height 2.5ft (75cm), spread 2ft (60cm).
Eryngium leavenworthii is an attractive annual which flowers quickly from seed, producing spiky glaucous foliage which changes to a rich purple colour on the cones and bracts. Height from 20-36in (50-90cm). Available from Thompson & Morgan.
Eryngium 'Magical Blue Globe' is a compact hardy perennial, ideal for hot, sunny borders. The silvery stems are topped with domed flowers, and surrounded by a collar of green bracts. Available from Thompson & Morgan.
Eryngium maritimum (common sea holly) produces silver-green leaves and metallic blue flowers. Height 18in (45cm).
Eryngium x tripartitum is a perennial with attractive blue-grey flowers in July-September. Height to 2.5 ft (75cm).
Eryngium x oliverianum is a hardy perennial with blue stems, deep-cut blue-green leaves and blue or pale purple flowers, surrounded by prickly bracts. Height from 2 to 3ft (60 - 90cm).
Eryngium planum has rounded deep blue flowers and dark green heart shaped foliage on upright stems, in summer. Height to 48in (120cm). Available from Gardening Express. Good cultivars include 'Blue Hobbit' a low maintenance dwarf variety that produces sprays of spiky electric blue flowers. Height and spread to 12in (30cm). Available from Thompson & Morgan, You Garden.
Eryngium varifolium is a small evergreen variety which grows to only 25in (35cm), with beautiful spiny dark-green-and-white veined leaves throughout the year. Available from Gardening Express.
Eryngium variifolium is a semi-evergreen perennial with glossy white-veined green leaves and metallic blue flower cones with white bracts. Height to 24in (60cm).
Eryngium zabelii 'Neptunes Gold' is a golden-leaved form with jagged rosettes of foliage and thistle-like blooms in the same golden colour before changing to a lovely steely blue. Available at You Garden.