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Herbaceous Perennial

Eryngium planum 'Tetra Petra'

blue eryngo 'Tetra Petra'

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 silvery-blue bracts which can also be very attractive if left on the plant after the flowering period

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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 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 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

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

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

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