Eryngium (Sea Holly) in Zone 4a & 4b
Eryngium planum
When to plant eryngium (sea holly) in zone 4b
Zones 4a and 4b share the same average frost dates in our data, so this page covers both.
Method: Start indoors: Start indoors from seed, then transplant outside. Eryngium (Sea Holly) needs a head start most zones can't give it by direct-sowing alone.
| Start indoors | Feb 13–Feb 20 |
|---|---|
| Direct sow / transplant outside | May 22–May 29 |
| Estimated bloom | May 21 '28–May 28 '28 (~365 days after transplanting) |
Spacing: 1 per square foot (square-foot-gardening spacing). Mature height: 2-3 ft.
Eryngium, commonly called sea holly, looks like a thistle crossed with a metal ornament, its spiny bracts taking on a blue or silvery sheen that holds up well both fresh and dried.
How eryngium (sea holly) fits zone 4's season
Zone 4b's frost-free window runs about 128 days, from May 15 to September 20. Eryngium (Sea Holly) needs about 365 days from transplant to first harvest.
Good companions
No standout companions recorded yet for Eryngium (Sea Holly).
Where to buy eryngium seeds
See why we recommend these suppliers →
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See it growing
Search YouTube for "growing eryngium (sea holly)" videos → (a live search, not a hand-picked video; results vary and aren't vetted by us)
← Back to the full zone 4b calendar · Full companion planting guide · Full plant profile · Plan your beds in the Garden Designer →
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Growing Eryngium (Sea Holly) in USDA zone 4b: when to start seeds indoors, when to direct-sow, and when to expect a bloom.
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