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Herbaceous Perennial

Eryngium planum 'Tetra Petra'
  • RHS Plants for pollinators

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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Size
Ultimate height
0.5–1 metres
Time to ultimate height
2–5 years
Ultimate spread
0.1–0.5 metres
Growing conditions
Chalk
Loam
Sand
Moisture
Well–drained
pH
Acid, Alkaline, Neutral
Colour & scent
StemFlowerFoliageFruit
Spring Green
Summer Blue Grey Silver Green
Autumn Green
Winter
Position
  • Full sun
Aspect

East–facing or South–facing or West–facing

Exposure
Exposed or Sheltered
Drought resistance
Yes
Hardiness
H5
Botanical details
Family
Apiaceae
Native to the UK
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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