How to Grow Eryngium - Sea Holly

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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.

Table of Contents

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

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.