Sea Holly Eryngium planum

👤 Non-toxic to humans
🐾 Non-toxic to pets
🌸 Blooming
🍪 Not edible
‍🌱 Easy-care
blue eryngo


The Eryngium planum, commonly known as Sea Holly, has a distinctive and striking appearance. It is characterized by its spiny-toothed leaves which are often a bluish or silvery-green color. The leaves form a rosette at the base of the plant, with smaller, more sparse leaves adorning the branching stems. Sea Holly's most notable feature is its cone-shaped flower head, which is surrounded by spiny bracts often resembling a collar. These flower heads are usually a metallic blue or violet color, giving the plant an almost alien, ornamental look. The texture of the plant is quite spiky, including the stems which can also take on a bluish hue. Overall, the plant presents a rather rugged yet alluring aesthetic, commonly used in gardens to provide a contrast with softer-leaved plants.

Plant Info
Common Problems

About this plant

  • memoNames

    • Family


    • Synonyms

      Flat Sea Holly, Blue Eryngo, Blue Hedgehog, Blue Thistle

    • Common names

      Eryngium affine, Eryngium amethystinum, Eryngium caucasicum, Eryngium cuneifolium, Eryngium firmum, Eryngium glaucophyllum, Eryngium latifolium, Eryngium noeanum, Eryngium planifolium, Eryngium poterioides, Eryngium spina-alba, Eryngium supinum, Eryngium sylvaticum, Eryngium variifolium.

  • skullToxicity

    • To humans

      Flat Sea Holly is generally considered non-toxic to humans, and there are no well-documented cases of poisoning from consuming or coming into contact with this plant. Therefore, ingestion of Eryngium planum, commonly known as Flat Sea Holly, is not typically associated with toxicity or adverse health consequences in humans.

    • To pets

      Flat Sea Holly is also not known to be toxic to pets, and there are no significant reports of pet poisoning from consuming or contacting this plant. As a result, ingestion of Eryngium planum, popularly known as Flat Sea Holly, does not pose a toxicity risk to pets, and no specific symptoms of poisoning are expected. However, it's always prudent to monitor pets around plants, as individual animals may have different sensitivities or reactions.

  • infoCharacteristics

    • Life cycle


    • Foliage type


    • Color of leaves


    • Flower color


    • Height

      2 feet (60 cm)

    • Spread

      1.5 feet (45 cm)

    • Plant type


    • Hardiness zones


    • Native area



  • money-bagGeneral Benefits

    • Attracts Pollinators: Eryngium planum, commonly known as Sea Holly, is known for its striking blue flowers that are highly attractive to bees, butterflies, and other beneficial insects, aiding in pollination in the garden.
    • Drought Tolerance: Sea Holly is well-adapted to dry conditions, making it ideal for xeriscaping or in gardens where water conservation is a priority.
    • Low Maintenance: This plant requires minimal care once established, tolerating poor soil and needing little in the way of fertilization or pruning.
    • Deer Resistance: The prickly texture and tough foliage of Sea Holly deter deer, making it a good choice for gardens in areas with high deer populations.
    • Ornamental Value: With its unique texture, striking flower heads and metallic blue color, Sea Holly serves as an attractive addition to bouquets and floral arrangements.
    • Long Blooming Period: Its extended blooming period from mid-summer to early autumn provides lasting visual interest in the garden.
    • Soil Erosion Control: The deep root system of Sea Holly helps to stabilize the soil, preventing erosion, particularly in sandy or coastal environments.
    • Winter Interest: The dried flower heads of Sea Holly can remain on the plant through winter, adding structural interest to garden landscapes during the colder months.

  • medicalMedical Properties

    • Anti-inflammatory: Eryngium planum has been traditionally used to reduce inflammation in various ailments.
    • Diuretic effect: The plant has been known to increase urine production, which can help in the management of certain urinary disorders.
    • Antioxidant properties: It contains compounds that are believed to have antioxidant effects, which may protect cells from oxidative stress.
    • Antimicrobial activity: The extract of the plant has been reported to possess antimicrobial properties against certain bacteria and fungi.
    • Wound healing: There is traditional usage of Eryngium planum preparations in promoting the healing of wounds.
    • Expectorant properties: The plant has been used to assist in clearing mucus from the respiratory tract.
    • Antispasmodic effects: It may help in relieving muscle spasms or cramps.

  • windAir-purifying Qualities

    This plant is not specifically known for air purifying qualities.

  • leavesOther Uses

    • Eryngium planum, commonly known as Sea Holly, can be used as a natural dye, producing a range of blue and green colors for textiles and artisan crafts.
    • Sea Holly is appreciated in floral arrangements for its unique texture and lasting color, often used in dried bouquets and as a fresh cut flower.
    • The plant can serve as an architectural feature in gardens due to its distinctive shape and striking blue flowers that add visual interest to landscape design.
    • Sea Holly has been utilized in traditional crafts, such as the making of wreaths and other decorative items, especially for festive occasions.
    • The plant is known to attract beneficial insects like bees and butterflies, enhancing pollination in gardens and agricultural settings.
    • Sea Holly is sometimes used in companion planting as it is believed to repel certain pests that would otherwise harm nearby plants.
    • The spiny leaves and stems of Sea Holly can act as a natural deterrent against garden pests like deer and rabbits, which tend to avoid its prickly texture.
    • Its root system helps to stabilize soil and prevent erosion, particularly in sandy or coastal areas where the plant thrives.
    • The striking appearance of Sea Holly makes it a popular choice for use in fashion and textile design, inspiring patterns and prints.
    • Sea Holly seeds are sometimes incorporated into bird food mixtures, attracting a variety of birds to gardens and providing them with a nutritious food source.

Interesting Facts

  • bedFeng Shui

    The plant Sea Holly is not used in Feng Shui practice.

  • aquariusZodiac Sign Compitability

    The plant Sea Holly is not used in astrology practice.

  • spiralPlant Symbolism

    • Protection: Eryngium planum, commonly known as Sea Holly, has thistle-like flowers and spiny leaves, suggesting its use in symbolism for protection and defense against negative forces.
    • Independence: With its hardy and resilient nature, Sea Holly is often associated with independence and the ability to thrive in challenging environments.
    • Persistence: The plant's ability to grow in poor soil and withstand drought conditions makes it a symbol of persistence and endurance.
    • Attractiveness: Despite its tough appearance, Sea Holly has striking blue flowers that symbolize an attractive quality, perhaps referencing the idea of "hidden beauty" or allure amidst a harsh exterior.

Every 2 weeks
2500 - 10000 Lux
Every 2-3 years
Spring-early summer
Not needed
  • water dropWater

    Sea holly should be watered deeply but infrequently to mimic the dry conditions of its native habitat. During the growing season, water approximately once a week, providing about one inch of water or around 0.6 gallons per plant especially if the weather is dry. It's important to let the soil dry out between waterings to prevent root rot. In winter, reduce watering significantly as the plant requires a drier dormancy period. Overwatering can be more detrimental than underwatering for this drought-tolerant species.

  • sunLight

    Sea holly thrives in full sunlight and should be placed in a location where it receives at least six hours of direct sunlight daily. Partial shade is tolerated, but too much shade can lead to weaker stems and less vibrant blooms. The best spot for sea holly is an open area with ample sunlight and good air circulation to promote healthy growth and prevent disease.

  • thermometerTemperature

    Sea holly is hardy and can tolerate a temperature range from about 40 degrees Fahrenheit at night up to around 85 degrees Fahrenheit during the day. It is cold hardy to USDA zone 5, which corresponds to minimum winter temperatures of approximately -20 to -10 degrees Fahrenheit. The ideal growing temperatures for sea holly are between 60 and 75 degrees Fahrenheit to encourage optimal growth and flowering.

  • scissorsPruning

    Sea holly benefits from pruning to remove spent flower heads and encourage further blooming. Prune dead or faded flowers during the flowering season to promote new growth. Periodic thinning of crowded clumps also improves air circulation and reduces the likelihood of disease. The best time for major pruning is in late winter or early spring before new growth begins to shape the plant and remove dead stems.

  • broomCleaning

    Not needed

  • bambooSoil

    Sea Holly (Eryngium planum) thrives best in a well-drained, sandy or loamy soil mix with moderate fertility. The ideal pH for Sea Holly ranges from 5.8 to 7.2, slightly acidic to neutral. Incorporating gravel or grit into the soil enhances drainage, which is essential for the plant's health.

  • plantRepotting

    Sea Holly (Eryngium planum) is typically not repotted frequently as it prefers to establish itself without disturbance. It should be repotted only when root-bound, roughly every 3 to 4 years, with care taken not to damage its taproot during the process.

  • water dropsHumidity & Misting

    Sea Holly (Eryngium planum) is tolerant of a wide range of humidity levels and prefers to be in drier conditions. It does not require high humidity and can thrive in the average humidity levels found in most temperate climates.

  • pinSuitable locations

    • Indoor

      Place in bright light, water sparingly, gritty soil mix.

    • Outdoor

      Full sun, well-drained soil, tolerant of drought.

    • Hardiness zone

      4-8 USDA

  • circleLife cycle

    Eryngium planum, commonly known as Sea Holly, begins its life cycle with seed germination, typically occurring in spring when temperatures are suitable for growth. After germination, the plant enters a vegetative state where it develops a rosette of spiny leaves close to the ground. As the plant matures, it sends up flowering stems in summer which bear small, metallic blue flowers clustered into thistle-like heads that attract a variety of pollinators. Following pollination, seeds are produced and dispersed, either by wind or by adhering to animals. Throughout fall and winter, the plant may die back, especially in colder climates, retreating to its root system where it can survive until the next growing season. In the following spring, either new plants will grow from the seeds or the existing root system will regenerate, repeating the lifecycle.

  • sproutPropogation

    • Propogation time

      Spring-early summer

    • Eryngium planum, commonly known as sea holly, is a durable perennial that is best propagated through seed. The optimal time to sow sea holly seeds is in late winter to early spring. To start, chill the seeds for a couple of weeks in the refrigerator to break dormancy, a process known as stratification. Prepare a seed starting mix in a tray or pots, and scatter the seeds over the surface, lightly covering them with soil. It's essential to keep the soil moist but not waterlogged. Place the tray or pots in a warm location with plenty of light, as this will help ensure successful germination. Once seedlings appear and have developed a few true leaves, they can be transplanted to their final location in the garden, keeping in mind that sea holly thrives in full sun and well-drained soil.