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Herbaceous Perennial

Eryngium × zabelii 'Blue Waves'

sea holly 'Blue Waves'

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

Synonyms

Eryngium Dove Cottage hybrid

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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

South–facing or West–facing or East–facing

Exposure

Exposed or Sheltered

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 the UK: 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

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