Eryngium × olivierianum 'Blue Waves'

RHS Plant Profile

eryngo 'Blue Waves'

RHS

Other common names

sea holly 'Blue Waves'

Synonyms

Eryngium × zabelii 'Blue Waves'
Eryngium Dove Cottage hybrid

Herbaceous Perennial

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An upright, clump-forming perennial to around 75cm tall with semi-evergreen, deeply divided green leaves with silvery veining. Large, intense steel-blue flowerheads surrounded by long, spiny bracts are borne in succession from early summer on stout, branching, blue stems

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: South–facing or West–facing or East–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: Semi evergreen
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 and protect from winter wet

Propagation

Propagate by root cuttings in late winter

Suggested planting locations and garden types

Architectural
Coastal
Cottage and informal garden
Prairie planting
City and courtyard gardens
Gravel garden
Patio and container plants
Banks and slopes
Cut flowers
Flower borders and beds

Pruning

No pruning required. 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