How to Grow Eryngium — Sea Holly

Eryngium Sea holly

Eryngium–commonly called sea holly–is an upright perennial with heart-shaped, divided green leaves. In summer, it produces tall blue stems topped with cone-shaped purple flowers surrounded by spiny bracts.

Eryngium is stiff-branched and thistle-like. There are 230 species in the Eryngium genus; some are fibrous-rooted and some are tap-rooted. Eryngium self sows.

Eryngium is an excellent cut and dried flower.

Alpine sea holly, Eryngium alpinum

Get to know Eryngium

  • Plant type: Perennial
  • Growing Zones and range: Zones 2 to 8 depending on the variety
  • Hardiness: Hardy to -20°F (-29°C)
  • Height and width: 2 to 7 feet (.6-2.1m) tall, depending on the variety
  • Foliage: Leaves are sparse, dark green, deeply cut, and spiny toothed.
  • Flowers: Tiny flowers are borne in dense, rounded, conelike umbles with a ruff of stiff, spiny bracts at the base
  • Flower colors: Blue, white
  • Bloom time: Midsummer to frost
  • Uses: Middle of borders; textural effects; dried arrangements
  • Common name: Sea Holly
  • Botanical name: Eryngium spp.
  • Family: Apiaceae
  • Origin: Europe, North Africa

Where to plant Eryngium

  • Grow Eryngium in full sun.
  • Eryngium will grow in poor, dry, and sandy soil. It grows well near the seaside.
  • Eryngium will tolerate heat and drought.

Eryngium uses and companions

  • Use Erynigium in bed and borders; beautiful against a dark background when backlit.
  • Eryngium is a good fresh-cut or dried flower.
  • Good garden companions for Eryngium include Artemisia, Limonium latifolium, Oenothera, Zauschneria.
Sea holly, Eryngium bourgatii
Sea holly, Eryngium bourgatii

When to plant Eryngium

  • Set established Eryngium plants in the garden in spring. Mature sea holly does not like transplanting.
  • Sow seeds in spring.

Planting and spacing Eryngium

  • Space Eryngium 2 feet (.6m) or more apart.
  • Sow seed 1/8 inch deep in containers or evenly prepared soil.

How to water and feed Eryngium

  • Eryngium needs moderate water; established plants are drought tolerant.
  • Fertilizing Eryngium can cause plants to grow tall and flop over.

Eryngium care

  • Eryngium is an excellent cut and dried flower.
  • For drying, pick just before bloom has fully opened and hang them in a warm, dry, dark place.

Eryngium pests and diseases

  • Eryngium is prone to root rot in wet soil especially in winter.
  • Sooty mold is a problem in humid conditions.
Flowers and bracts of sea holly, Eryngium
Flowers and bracts of sea holly, Eryngium

Eryngium propagation

  • Propagate Eryngiumgium by separating small plantlets from the base of the clump.
  • Tap-rooted plants are difficult to divide.
  • Erynigium seed germinates in 12 to 20 days at 68° to 70°F (20°-21°C).
  • Plants self-sow and seedlings are easily moved.

Eryngium varieties to grow

  • Erynigium agavivolium is an evergreen species that grows to 5 feet tall with greenish-white flower heads with spiny bracts.
  • E. alpinum grows to 2 feet tall with deeply cut blue bracts; ‘Blue Star’ is a good variety.
  • A. amethystinum, amethyst sea holly, grows to 2 feet tall bears round, metallic blue flower heads with silver-gray bracts; s cold hardy in Zones 2-8.
  • E. giganteum, giant seas holly is a short-lived perennial that grows to 3 feet tall; bears steel blue flowers,
  • E. pandanifolium, giant sea holly, grows 6 to 7 feet tall and 4’ wide in Zones 8-10.
  • E. planum, flat sea holly is an evergreen species that grows to 3 feet tall and bears pale steely blue flowers surrounded by blue-green bracts.
  • E. yuccifolium bears sword-shaped blue-green leaves and whitish-green flowers; grows to 4 feet tall.

Eryngium amethystinum – Amethyst sea holly

Eryngium amethystinum bears stiff and prickly and spiny blue flower heads. Eryngium adds architectural interest and color contrast to a garden. Several species are popular, but the Eryngium amethystinum is the most cold hardy and very showy. Tall-branched flowering stems, which may be blue, arise from a cluster of basal foliage. This is the only sea holly with spiny, pinnately compound leaves. The flowers are showy from midsummer to frost and look rather like thimbles framed by a starlike ring of steely blue bract.

  • Size: 1 ½ to feet tall; 2 feet wide.
  • Light: Full Sun.
  • Soil and moisture: Poor, dry, sandy soil; tolerates drought and seashore conditions.
  • Planting and propagation: Plant container-grown plants in spring, spacing 2 feet apart. Separate plantlets from plant base in fall.
  • Special care: Resents transplanting. May flop in fertile soil. Pick flowers for drying when fully open for best color retention.
  • Pest and diseases: May rot in winter-wet site. Sooty mold may disfigure flowerds if humidity is high; improve air circulation.
  • Climate: Zones 2-8.
  • Cultivars and similar species: E. giganteum, 4 to 6 feet tall, silvery all over, a biennial that dies after flowering but self-seeds; ‘Miss Willmott’s Ghost,’ nearly white bracts, E. alpinum: very blue pineapple-shaped flowers with finely divided soft bracts, heart-shaped lower leaves, palmately lobed upper leaves, Zones 4-8; ‘Amethyst,’ metallic blue, 3 feet tall; ‘Opal,’ metallic blue, 2 feet tall; ‘Superbum,’ dark blue flowers, 2 to feet tall. E. bourgatti: compact, white-veined, spiny palmate silvery foliage, blue-green flowers with long, spiny bracts. Zones 4-8.
  • Garden use: Striking plant in beds and borders where adapted. Beautiful against dark background and when backlit. Good fresh-cut or dried flower.

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