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Herbaceous Perennial

Eryngium × olivierianum 'Cobalt Star'

eryngo 'Cobalt Star'

A herbaceous perennial with stiffly branched, dark blue stems and spiny, divided leaves with silvery veins. In mid-summer to early autumn produces cones of tiny blue flowers surrounded by narrow, spiny, bluebracts

Synonyms

Eryngium 'Cobalt Star'
Eryngium × zabelii 'Cobalt Star'

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Ultimate height

0.5–1 metres

Time to ultimate height

2–5 years

Ultimate spread

0.1–0.5 metres

Chalk

Loam

Sand

Moisture

Well–drained

pH

Acid, Alkaline, Neutral

	Stem	Flower	Foliage	Fruit
Spring
Summer
Autumn
Winter

Full sun

Aspect

East–facing or South–facing or West–facing

Exposure

Exposed

Drought resistance

Yes

Hardiness
Hardiness ratings
All ratings refer to the UK growing conditions unless otherwise stated. Minimum temperature ranges (in degrees C) are shown in brackets
H1a: under glass all year (>15C)
H1b: can be grown outside in the summer (10 - 15)
H1c: can be grown outside in the summer (5 - 10)
H2: tolerant of low temperatures, but not surviving being frozen (1 to 5)
H3: hardy in coastal and relatively mild parts of the UK (-5 to 1)
H4: hardy through most of the UK (-10 to -5)
H5: hardy in most places throughout the UK even in severe winters (-15 to -10)
H6: hardy in all of UK and northern Europe (-20 to -15)
H7: hardy in the severest European continental climates (< -20)

Botanical details

Family: Apiaceae
Native to GB / Ireland: No
Foliage: Deciduous
Habit: Clump forming
Genus: Eryngium can be annuals, biennials or perennials with simple or divided leaves, often spiny edged, and cone-like flower-heads often surrounded by an involucre of conspicuous spiny bracts
Name status: Accepted

How to grow

Cultivation

Grow in dry, well-drained soil that is poor to moderately fertile. Full sun is essential as is protection from winter wet

Propagation

Propagate by root cuttings in late winter

Suggested planting locations and garden types

City and courtyard gardens
Coastal
Cottage and informal garden
Gravel garden
Cut flowers
Flower borders and beds

Pruning

Although you can cut back flower stems after flowering the seedheads are a very attractive feature so are usually left over winter

Pests

May be susceptible to leaf and bud eelworms, and slugs and snails

Diseases

May be susceptible to root rot and powdery mildews

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