Eryngium x oliverianum (Oliver Sea Holly) is an upright perennial with basal rosettes of heart-shaped, strongly toothed, dark green leaves. From mid-summer to early fall, sturdy leafy violet-blue stems bear large, cone-shaped, thistle-like, blue to lavender-blue flower heads. Each flower head is surrounded by narrow, spiny, metallic-blue bracts. Attractive to bees and butterflies but deer resistant, this striking Sea Holly survives in a wider range of soil types than many more difficult eryngiums. Eryngium x oliverianum is a cross between E. planum and E. giganteum. According to many, it has the strongest blue stems and flowers of any eryngiums.
- Recipient of the prestigious Award of Garden Merit of the Royal Horticultural Society.
- Grows in clumps of stiffly erect, branched stems up to 24-36 in. tall (60-90 cm) and 18-24 in. wide (45-60 cm)
- Performs best in full sun in fairly dry, poor to moderately fertile well-drained soils. Tolerates light shade, poor soils, drought and salt.
- Excellent choice for gravel gardens, cottage gardens and coastal gardens. May be planted as a single specimen or in groupings. Perfect for cut or dried flower arrangements too!
- Although you can cut back flower stems after flowering the seedheads are a very attractive feature so are usually left over winter
- Watch for leaf and bud eelworms, powdery mildew and root rot.
- Propagate by root cuttings in late winter