Eryngium (Sea Holly) in Zone 7a & 7b
Eryngium planum
Yes, eryngium (sea holly) grows in zones 7a and 7b. Start seeds indoors Jan 9–Jan 16 and plant out Apr 17–Apr 24.
When to plant eryngium (sea holly) in zone 7b
Zones 7a and 7b share the same average frost dates, so this page covers both.
Method: Start indoors: Start indoors from seed, then transplant outside. It needs a head start most zones can't give it by direct-sowing alone.
| Start indoors | Jan 9–Jan 16 |
|---|---|
| Direct sow / transplant outside | Apr 17–Apr 24 |
| Estimated bloom | About a year after planting |
Spacing: 1 per square foot (square-foot-gardening spacing). Mature height: 2-3 ft.
Plant alongside it in zone 7b
These go outside within two weeks of eryngium (sea holly) in zone 7b, so one planting day can cover them.
- NasturtiumApr 17–Apr 24
- MarigoldApr 17–Apr 24
- Ageratum (Flossflower)Apr 17–Apr 24
- AmaryllisApr 17–Apr 24
- Annual Geranium (Pelargonium)Apr 17–Apr 24
- Butterfly Weed (Asclepias)Apr 17–Apr 24
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 7's season
Zone 7b's frost-free window runs about 198 days, from April 10 to October 25. Eryngium (sea holly) takes about a year from planting to first bloom, so it spans more than one growing season.
Eryngium (Sea Holly) planting windows in every zone
Zone 7b is highlighted. Useful for comparing against a neighbouring zone, or for a garden somewhere else.
| Zone | Start indoors | Sow or plant out | Bloom |
|---|---|---|---|
| 3a & 3b | Feb 28–Mar 7 | Jun 6–Jun 13 | About a year after planting |
| 4a & 4b | Feb 13–Feb 20 | May 22–May 29 | About a year after planting |
| 5a & 5b | Feb 8–Feb 15 | May 17–May 24 | About a year after planting |
| 6a & 6b | Jan 24–Jan 31 | May 2–May 9 | About a year after planting |
| 7a & 7b (your zone) | Jan 9–Jan 16 | Apr 17–Apr 24 | About a year after planting |
| 8a & 8b | Dec 24–Dec 31 | Apr 1–Apr 8 | About a year after planting |
Good companions
No well-established companions for eryngium (sea holly).
Where to buy eryngium seeds
None of the seed suppliers we list carries eryngium seeds right now. A local garden center or a specialty seed house is the place to look.
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 7b calendar · Plan your beds in the Garden Designer →
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Growing Eryngium (Sea Holly) in USDA zone 7b: when to start seeds indoors, when to direct-sow, and when to expect a bloom.
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