Eryngium × olivierianum 'Blue Steel'

RHS Plant Profile
eryngo 'Blue Steel'

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Other common names

sea holly 'Blue Steel'

Synonyms

Eryngium × zabelii 'Blue Steel'
Eryngium 'Blue Steel'
Eryngium biebersteinianum 'Blue Steel'

Herbaceous Perennial

A robust, clump-forming perennial with erect branched stems and spiny, highly divided dark green leaves. Flowering in summer, it has abundant small thimble shaped flower-heads with spiky steely deep-blue bracts which can also be very attractive if left on the plant after the flowering period

Position

Full sun

Soil Types

Chalk, Loam, Sand

Max Height

0.5-1 metres

Max Spread

0.1-0.5 metres

Size

Time to Maturity
2–5 years
Max Spread
0.1-0.5 metres
Max Height
0.5-1 metres

Growing Conditions

Chalk Loam Sand
Moisture
Well–drained
pH
Acid or Alkaline or Neutral

Position

Full sun
Aspect
East–facing or South–facing or West–facing
Exposure
Exposed or Sheltered
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)
H5
Drought Resistance
Yes

Colour & Scent

Season Stem Flower Foliage Fruit
Spring
Summer
Autumn
Winter

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
Unresolved

How to Grow

Cultivation

Will grow well in poor, moderately fertile, well-drained soil in full sun avoiding wet winter conditions

Propagation

Propagate by seed, by root cuttings in late winter and by division in spring

Suggested planting locations and garden types

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

Pruning

Cut back any dead foliage throughout the season and but leave spent flowers for winter interest. Cut flowers before they open for floristry purposes

Pests

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

Diseases

May be susceptible to root rot and powdery mildews