Sea Holly

Eryngium planum

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verifiedReviewed by the GreenScout Team

An eye-catching perennial with distinctive blue, thistle-like flower heads and spiky blue-tinted foliage that creates architectural interest in the garden. The flowers bloom from mid to late summer and are excellent for cutting and drying. This drought-tolerant plant is extremely hardy and thrives in poor, well-drained soils with minimal care.

Common Problems

Select the problem your Sea Holly is experiencing to get a treatment guide.

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Overwateringchevron_right

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Root Rotchevron_right

Care Guide

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Light

Full sun (6+ hours daily)

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Water

Low to moderate; water sparingly once established. Drought tolerant.

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Soil

Well-drained, poor to moderately fertile soil. Prefers sandy or gravelly conditions.

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Fertiliser

Minimal; avoid overfeeding. Optional light spring feeding.

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Temperature

Hardy perennial; tolerates cold winters and coastal conditions.

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Humidity

Low to moderate; prefers drier conditions.

Toxicity

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Non-toxic, though spiky foliage may cause minor skin irritation.

Common Diseases

filter_dramaRoot Rotchevron_right

Common Pests

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Seasonal Care

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Resume regular watering and feeding as growth picks up.

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Peak growing season. Water and feed regularly.

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Reduce watering as growth slows. Stop heavy feeding.

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Minimal watering and feeding. Protect from frost if needed.

Frequently Asked Questions

Why does my Sea Holly have spiky, thistle-like blooms?

Its distinctive blue, thistle-like flower heads and spiky blue-tinted foliage create the architectural interest it's grown for — the spikiness may cause minor skin irritation, so handle with care when cutting.

Why did my Sea Holly rot after a wet season?

It's extremely drought-tolerant and prefers poor, well-drained soil — consistently wet or waterlogged conditions are its main vulnerability, quickly leading to root rot.