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Eryngium planum is often confused with:
Cirsium arvense Carduus muticus
Eryngium aquaticum Eryngium aquaticum
Native alternative(s) for Eryngium planum:
Eryngium yuccifolium In the summer.
Plants that fill a similar niche:
Salvia rosmarinus Rosmarinus officinalis
Salvia nemorosa Form in bloom
Thymus vulgaris Thymus vulgaris

Sea Star Thistle Eryngium planum

Phonetic Spelling
er-RIN-jee-um
Description

Sea holly is a perennial plant in the Apiaceae (carrot) family.  It grows in stiff erect clumps 1 to 3 feet tall and 1 to 2 feet wide and provides interest in the landscape with its unusual spiky flower heads that resemble a thistle.  The name Eryngium is a Greek reference to the spiny nature of this genus of plants.  The species name planum means flat.

Plant in the full sun in well drained sandy or loamy soil.  In fact, the more sun this plant recieves the more intensely colored the blue flowers will be.  It is tolerant of a wide range of soil pH.

This plant blooms from June through September and often profusely during the summer.  It has ornamental interest in the colorful,  spiny, thick, and white-veined leaves.  Steel blue flowers with a ring of spiky ornamental bracts are useful for cutting or drying. Dead head flowers to maintain a tidy appearance cut the plant back after flowering at the end of the summer.  The plant sometimes self seeds, slowly moving around the garen but rarely becomes a problem.  Propagation is most easily accomplished by separating plantlets from the base of the parent plant.   Choose a location wisely as sea holly does not transplant well.

Sea holly is tolerant of poor or dry soils, and its spiny leaves are resistant to browsing by rabbits and deer.  It withstands salty, coastal winds and also does well in inland gardens.  Use in small groupings in a cottage garden, rock garden or as a specimen in a perennial border planting.  Plant in a container or along a patio to enjoy the unusual blooms that are frequented by butterflies.

Insects, Diseases, and Other Plant Problems:   Aphids, slugs, and snails may appear. Susceptible to root rot (needs dry soils and leaf spot diseases.   In rich soils plants may grow leggy and topple over.

See this plant in the following landscape:
Cultivars / Varieties:
  • 'Blue Cap'
    Clump forming, blue tinged leaves
  • 'Blue Glitter'
    Intense blue flower color, quick maturity
  • 'Blue Hobbit'
    Dwarf reaching only 1 ft. tall and wide, purple blue flower heads
  • 'White Glitter'
    Silver ivory flowers, silver green stems
'Blue Cap', 'Blue Glitter', 'Blue Hobbit', 'White Glitter'
Tags:
#showy flowers#full sun tolerant#drought tolerant#perennials#specimen#purple flowers#blue flowers#low maintenance#cottage garden#rabbit resistant#long-lasting flowers#summer flowers#deer resistant#spiny leaves#rock garden#border planting#cutting garden#pollinator plant#flowers mid-summer#dried arrangements#poor soils tolerant#flowers early summer#flowers late summer#small group plantings#patio planting#dry soils tolerant#unusual flowers#butterfly friendly#bee friendly#container plant#coastal plant
 
Cultivars / Varieties:
  • 'Blue Cap'
    Clump forming, blue tinged leaves
  • 'Blue Glitter'
    Intense blue flower color, quick maturity
  • 'Blue Hobbit'
    Dwarf reaching only 1 ft. tall and wide, purple blue flower heads
  • 'White Glitter'
    Silver ivory flowers, silver green stems
'Blue Cap', 'Blue Glitter', 'Blue Hobbit', 'White Glitter'
Tags:
#showy flowers#full sun tolerant#drought tolerant#perennials#specimen#purple flowers#blue flowers#low maintenance#cottage garden#rabbit resistant#long-lasting flowers#summer flowers#deer resistant#spiny leaves#rock garden#border planting#cutting garden#pollinator plant#flowers mid-summer#dried arrangements#poor soils tolerant#flowers early summer#flowers late summer#small group plantings#patio planting#dry soils tolerant#unusual flowers#butterfly friendly#bee friendly#container plant#coastal plant
  • Attributes:
    Genus:
    Eryngium
    Species:
    planum
    Family:
    Apiaceae
    Life Cycle:
    Perennial
    Recommended Propagation Strategy:
    Division
    Seed
    Country Or Region Of Origin:
    E. Central Europe to Mongolia and W. Himalaya
    Wildlife Value:
    The flowers attract butterflies and bees.
    Dimensions:
    Height: 2 ft. 0 in. - 3 ft. 0 in.
    Width: 1 ft. 0 in. - 2 ft. 0 in.
  • Whole Plant Traits:
    Plant Type:
    Perennial
    Habit/Form:
    Clumping
    Erect
    Maintenance:
    Low
    Texture:
    Coarse
    Appendage:
    Prickles
  • Cultural Conditions:
    Light:
    Full sun (6 or more hours of direct sunlight a day)
    Soil Texture:
    Loam (Silt)
    Sand
    Soil pH:
    Acid (<6.0)
    Alkaline (>8.0)
    Neutral (6.0-8.0)
    Soil Drainage:
    Good Drainage
    Occasionally Dry
    Very Dry
    Available Space To Plant:
    12 inches-3 feet
    NC Region:
    Coastal
    Mountains
    Piedmont
    USDA Plant Hardiness Zone:
    5a, 5b, 6b, 6a, 7a, 7b, 8a, 8b, 9b, 9a
  • Fruit:
    Fruit Type:
    Schizocarp
  • Flowers:
    Flower Color:
    Blue
    Gray/Silver
    Purple/Lavender
    Flower Inflorescence:
    Umbel
    Flower Value To Gardener:
    Good Cut
    Good Dried
    Long-lasting
    Showy
    Flower Bloom Time:
    Summer
    Flower Size:
    < 1 inch
    Flower Description:
    The long lasting flower head is a spherical-cylindrical umbel, 2 inches across packed with tiny, stemless, steel violet-blue flowers. A narrow, spiky collar of spiny, blue-green bracts surrounds the flower.
  • Leaves:
    Leaf Color:
    Green
    Leaf Feel:
    Prickly
    Leaf Type:
    Simple
    Leaf Arrangement:
    Rosulate
    Leaf Shape:
    Elliptical
    Oblong
    Leaf Margin:
    Dentate
    Hairs Present:
    No
    Leaf Length:
    > 6 inches
    Leaf Description:
    Deeply toothed spiny basal elliptic to oblong with a cordate base form rosettes that reach 14" wide.
  • Stem:
    Stem Is Aromatic:
    No
  • Landscape:
    Landscape Location:
    Container
    Patio
    Rock Wall
    Slope/Bank
    Small Space
    Landscape Theme:
    Butterfly Garden
    Cottage Garden
    Cutting Garden
    Drought Tolerant Garden
    Pollinator Garden
    Rock Garden
    Design Feature:
    Border
    Small groups
    Specimen
    Attracts:
    Bees
    Butterflies
    Resistance To Challenges:
    Deer
    Drought
    Dry Soil
    Poor Soil
    Rabbits
    Salt
    Problems:
    Spines/Thorns