Sea holly (Eryngium planum 'Blue Glitter')

Overview

Eryngium planum ‘Blue Glitter’, commonly known as sea holly, is highly valued for its unique, architectural presence and striking steel-blue coloration. This coarse, clump-forming perennial provides textural contrast in the garden long after typical blooms fade. The cultivar ‘Blue Glitter’ is especially celebrated for prolific branching, showcasing abundant, glittering steel blue flower heads throughout the summer season.

This plant thrives under conditions that stress many other garden specimens, namely poor soils and intense heat. Its low maintenance needs make Eryngium planum ‘Blue Glitter’ an excellent choice for contemporary or xeriscape landscape designs where drought tolerance is paramount. Once established, the sea holly is reliably hardy and offers excellent utility for fresh arrangements and long-lasting dried crafts.

Fast Facts

• Plant Family: Apiaceae
• Plant Type: Herbaceous perennial
• Hardiness Zones: USDA Zones 5-8
• Size at Maturity:
  • Height: 2-3 ft
  • Spread: 1-1.5 ft
• Bloom Time: June to September
• Bloom Description: Steel blue
• Sun Exposure: Full sun
• Water Needs: Dry
• Maintenance Level: Low

How to Grow

Plant sea holly in dry, sandy, well-drained soils. It thrives when given full sun exposure and generally tolerates poor soil conditions well; avoid overly rich mediums which can encourage sprawling. Because this is a taprooted plant, it transplants poorly and should be placed carefully where its final location is intended, as it prefers to be left undisturbed once established.

Water needs for Eryngium planum ‘Blue Glitter’ are minimal once the plant has settled in, requiring dry soil conditions to prevent root rot. Avoid overwatering at all costs. Fertilizing is generally unnecessary; rich soil amendments can negatively impact its rigid structure.

As a low-maintenance perennial, cleanup is straightforward. Stems may be cut back after the foliage dies back in late fall or early spring. Gardeners looking to maximize the viewing period can leave the dried flower heads for winter interest. Although it spreads slowly, allowing the established clumps naturalize offers a steady return each year.

Landscape Uses

The structural form and intense blue color of Eryngium planum ‘Blue Glitter’ make it an excellent focal point or textural element within mixed beds and borders. It excels in sun-baked areas where many softer perennials struggle, offering reliable four-season structure. Consider using it as a single specimen to highlight its unique habit or grouping three to five plants for a bolder mass display of steel-blue interest.

Due to its dry soil and full sun requirements, the sea holly pairs beautifully with other drought-tolerant plants such as ornamental grasses, Sedums, and lavender. Its distinctive texture contrasts well against fine-leaved plants, providing necessary visual weight in the landscape design. Furthermore, the sturdy stems ensure that this perennial contributes height and architecture without needing staking.

Standout Features

Flower Qualities

• Showy
• Good Cut
• Good Dried

Noteworthy Characteristics

Eryngium planum, commonly called sea holly, is a coarse, clump-forming perennial that features a summer bloom of steel-blue, thistle-like flower heads on branched stems rising from a rosette of dark green basal leaves. The cultivar ‘Blue Glitter’ is particularly noted for producing an abundant crop of “glittering” steel blue flower heads on heavily branched stems throughout summer, making it an excellent addition to the home garden.

Tolerances

• Drought
• Dry Soil

Potential Problems

Eryngium planum ‘Blue Glitter’ typically avoids serious insect or disease issues, provided its basic cultural needs are met. The most significant threat comes from overly moist conditions, as sea holly is highly susceptible to root rot if the soil retains too much water. Ensure excellent drainage to mitigate this risk.

Gardeners should monitor for localized leaf spot diseases, which can sometimes appear, especially in humid climates or if overhead watering occurs. Slugs and snails may occasionally target young foliage; early season vigilance or preventative measures can manage these soft-bodied pests effectively.

Frequently Asked Questions

What hardiness zones is Sea holly suitable for?

Eryngium planum ‘Blue Glitter’ is reliably hardy in USDA Zones 5 through 8.

How large does Sea holly grow?

This perennial typically reaches a height of 2 to 3 feet, spreading between 1 and 1.5 feet wide at maturity.

When does Sea holly bloom?

The exceptional steel blue blooms of Eryngium planum ‘Blue Glitter’ appear consistently from June through September.

What sun exposure does Sea holly need?

This variety absolutely requires full sun exposure to maintain its best habit and flower production.

Conclusion

The architectural form and outstanding steel blue coloration provided by Eryngium planum ‘Blue Glitter’ sea holly make it an invaluable, drought-tolerant component for the modern garden. Its tolerance for poor soil and reliability when dry ensures low maintenance success. Before planting, confirm that your site offers full sun and sharp drainage, matching the needs of this unique perennial.

Companion Planting

Selecting companions that share the dry, sunny habitat requirements of Eryngium planum ‘Blue Glitter’ will result in the healthiest, most visually cohesive planting scheme. Pair the sea holly with silver-leaved drought lovers such as Russian Sage (Perovskia atriplicifolia) or Artemisia to intensify the cool blue tones of its flowers.

For seasonal interest, plant drifts of summer-blooming Coneflowers (Echinacea) or Black-Eyed Susans (Rudbeckia). These warmer yellow and orange tones provide a beautiful, complementary contrast to the steely spikes of the sea holly throughout July and August. Ensure companions do not create dense shade beneath the Eryngium.

Design Ideas for Xeriscaping

The inherent drought tolerance of sea holly makes it a cornerstone plant for sustainable, low-water landscape design. Groupings of Eryngium planum ‘Blue Glitter’ planted along a sunny, south-facing border create reliable structure without demanding supplemental irrigation once established. Use light-colored gravel mulch near the planting zone to further retain heat and emphasize the dry aesthetic.

In contemporary garden settings, the rigid, thistle-like form works well juxtaposed against smooth, geometric hardscaping elements like retaining walls or monochromatic paving stones. The plant’s unique texture, especially the spiky collar of bracts surrounding the flower heads, adds necessary visual roughness and intricate detail within structured layouts.