Eryngium planum 'Seven Seas'

RHS Plant Profile

blue eryngo 'Seven Seas'

Synonyms

Eryngium 'Seven Seas'

Herbaceous Perennial

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'Seven Seas' is a clump-forming perennial to 90cm with rounded basal leaves. Upright, branching stems bear deeply-lobed, blue-tinged, spiny leaves and small, dark blue, terminal flower-heads with narrow, spiny bracts in summer and early autumn

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: 1–2 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
Exposure: 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: Accepted

How to Grow

Cultivation

Grow in dry, well-drained poor to moderately fertile soil in full sun, with protection from winter wet

Propagation

Propagate by division during spring, although they may be slow to re-establish, or insert root cuttings in late winter

Suggested planting locations and garden types

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

Pruning

Tidy plants after flowering; ideal for flower arranging - cut the stems before the flowers are fully open

Pests

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

Diseases

May be susceptible to root rot and powdery mildews