Sea holly (Eryngium maritimum)

Also known as: Seaside coyote-thistle

Sea holly (Eryngium) is a striking perennial often found along European coastlines. Known for its spiky, metallic blue or silver flowers and spiny foliage, it blooms from mid-summer to early fall.

**Key Characteristics:**
- Height: Typically 1 to 3 feet
- Flower Color: Metallic blue or silver
- Bloom Time: Mid-summer to early fall
- Wildlife: Attracts bees and butterflies
- Conservation: Considered endangered in some regions

**Growing Requirements:**
- Light: Prefers full sun
- Soil: Thrives in well-drained, sandy or loamy soil
- Water: Low to moderate; drought-tolerant
- USDA Hardiness Zones: 4-9
- Maintenance: Minimal care needed; deadheading can prolong blooming

Sea holly is a resilient plant that adds unique texture and color to gardens, making it ideal for xeriscaping and coastal landscapes.

In This Article

Care Tips Water Sunlight Temperature Soil Fertilize Prune Propagation Repotting

Attributes of Sea holly

Lifespan

Perennial, Biennial

Plant Type

Herb

Plant Height

60 cm to 90 cm

Spread

60 cm to 90 cm

Leaf Color

Green White Silver Blue Gray

Flower Size

1-2 cm

Flower Color

Blue

Images of Sea holly

Quickly Identify Sea holly

Eryngium maritimum can be identified by its deeply divided, spiny leaves that are bluish-green in color, and by its globular flower heads that are also blue and thistle-like.

Scientific Classification of Sea holly

Phylum

Vascular plants

Class

Dicotyledons

Order

Apiales

Family

Umbellifers

Genus

Eryngos

Species

Sea holly

Planting and Growing of Sea holly

Care Difficulty

Easy

Watering Schedule

Every 2 days

Sunlight Requirements

Full sun

Sunshine Duration

6-10 hours

Ideal Temperature

60-75℉

Soil Type

Potting Mix, Peat Mix

Soil pH

6.5-7.5

Fertilizer Type

Balanced

Pruning Season

Spring, Summer

Pruning Area

Branches, Leaves

Pruning Frequency

Once a year

Repotting Season

Spring

Pot Type

Plastic, Ceramic

How to Water Sea holly?

Eryngium maritimum requires a modest amount of water, approximately 250 ml per watering session. This amount ensures that the soil remains moist but not soggy, which is crucial for its roots' health. The key is to allow the top layer of the soil to dry out between waterings, as this plant is adapted to coastal conditions where water retention is minimal.

What are the symptoms of an underwatered Sea holly? ›

What should I do if my Sea holly is not getting enough water? ›

What are the symptoms of an overwatered Sea holly? ›

How to save an overwatered Sea holly? ›

What Are the Sunlight Requirements for Sea holly?

Sunlight Requirements: Full sun, Partial sun

Duration of light: Six to eight hours

Eryngium maritimum thrives in full sun to partial sun environments, best suited for areas receiving six to eight hours of sunlight a day. This exposure fosters healthy, vibrant growth and abundant flowering.

What is the ideal light condition for Eryngium maritimum? ›

How can I ensure Eryngium maritimum gets the best light? ›

What benefits does Eryngium maritimum gain from optimal sunlight? ›

More About Sunlight Requirements Techniques→

What Is the Ideal Temperature Range for Sea holly?

Ideal Temperature: 60 ~ 75℉

The ideal temperature range for Eryngium maritimum is between 60°F and 75°F. This range provides optimal conditions for growth by ensuring enough warmth to stimulate metabolic processes while avoiding excessive heat that could stress the plant. Temperatures within this range mimic the natural coastal habitats where these plants thrive, typically resulting in healthier foliage and better growth rates.

What Soil is Best for Sea holly?

Soil type: Sandy soil, Sand soil, Calcareous soil

Soil PH: 6.5 ~ 7.5

Eryngium maritimum thrives in well-drained soils to prevent root rot and other moisture-related issues. Well-drained conditions help the roots access oxygen, promoting strong and healthy growth of the plant. Adapting to nutrient-poor soils is one of the strengths of Eryngium maritimum. It thrives in environments where other species might struggle, emphasizing its minimal fertilization needs to achieve its characteristic silvery foliage and striking blue flowers. This plant is adept at handling saline environments, making it well-suited for coastal areas. This tolerance allows it to thrive where salt sprays can devastate less hardy species, contributing to its natural beauty in these unique landscapes.

How to Fertilize Sea holly?

Fertilizer type: Balanced

Eryngium maritimum, commonly known as sea holly, typically thrives with minimal fertilization. When fertilizing, use a balanced fertilizer at one-half the strength recommended for standard use. This helps ensure that the plant receives adequate nutrients without overwhelming its systems.

How to Prune Sea holly?

Pruning Time: Spring, Summer

Begin by identifying dead or damaged stems. Use clean, sharp pruning shears to cut these stems back to the base. This encourages healthy new growth and helps maintain a tidy appearance. Trim the plant to maintain its natural shape, avoiding excessive cutting to preserve its structural form. Once flowering has finished, remove spent flower heads by cutting them back to the nearest healthy leaf node. This prevents seed formation, which can sap energy from the plant, and encourages a second flush of blooms if done in early summer. More About Pruning Techniques→

How to Propagate Sea holly plant?

Propagate Time: Spring, Early summer

Harvest seeds from mature Eryngium maritimum flowers at the end of their blooming period. Ensure seeds are completely dry before storage to prevent mold or decay.

Select healthy stems and use a sharp knife to make clean cuts. Cuttings should be around 4-5 inches long, with leaves removed from the lower part to facilitate rooting.

Place seeds in a seed tray filled with well-draining soil mix. Cover lightly with soil and keep the tray in a warm, sunny location. Maintain consistent moisture until germination occurs.

More About Propagating Techniques→

How to Repot Sea holly plant?

Repotting frequency: Every 2-3 years

Eryngium maritimum shows signs that it's ready for repotting when its roots start protruding from the drainage holes or the plant appears stunted despite proper care. Ideally, repotting should occur during the active growing season in spring or summer to minimize transplant shock.

Select a pot that is slightly larger than the current one and has good drainage holes. Ceramic or terracotta pots are beneficial as they allow for better air exchange and stabilization. Such pots ensure your Eryngium maritimum avoids potential waterlogging and encourages root health.

Opt for sandy, well-drained soil that mimics its natural coastal habitat. This type of soil prevents water retention, reducing the risk of root rot. Adding grit or perlite to the soil mix can further enhance drainage, catering to the plant's preference for arid conditions.