Flat sea holly Eryngium planum
Flat sea holly (Eryngium planum) is a deciduous perennial flowering plant in the Apiaceae family, native to Central and eastern Europe to Central Asia. It grows 60–90 cm (24–35 in) tall and 40–60 cm (16–24 in) wide, wants full sun and low water, and is hardy to about -30 °C (-22 °F). Space plants about 50 cm (20 in) apart.
Plan Flat sea holly in your garden →
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Flat sea holly at a glance
| Type | Perennial flowering plant, deciduous |
|---|---|
| Family | Apiaceae |
| Mature height | 60–90 cm (24–35 in) |
| Mature spread | 40–60 cm (16–24 in) |
| Spacing | 50 cm (20 in) centre to centre |
| Sun | Full sun, at least 6 h of direct sun a day |
| Water | Low; drought tolerance high, waterlogging tolerance none |
| Soil pH | 6–8 |
| Cold hardiness | About -30 °C (-22 °F) once established (roughly USDA zone 4) |
| Heat stress | Likely above about 35 °C (95 °F) |
| Flowering | from about July for 5–7 weeks (northern hemisphere; later in cold climates, earlier in warm ones) |
| Wind tolerance | Moderate |
| Pollinator value | High |
| Edible | Not grown as food |
| Native to | Central and eastern Europe to Central Asia |
| Common in gardens of | 🇬🇧 United Kingdom, 🇩🇪 Germany |
Is Flat sea holly toxic?
- People: not well documented
- Cats: not well documented
- Dogs: not well documented
No toxicity data found in ASPCA or standard poison references; spiny bracts can scratch skin.
If a child or pet may have eaten part of a plant, call a poison centre or vet straight away.
Companion planting: what to grow with Flat sea holly
No well-documented helpful pairing. Group it with plants that like full sun and low water.
Questions about Flat sea holly
- How far apart should I plant Flat sea holly?
- About 50 cm (20 in) apart, centre to centre. A mature plant spreads 40–60 cm (16–24 in).
- Does Flat sea holly need full sun?
- Full sun: at least 6 hours of direct sun a day.
- How much water does Flat sea holly need?
- Low water. Drought tolerance is high and waterlogging tolerance none.
- How cold-hardy is Flat sea holly?
- It tolerates about -30 °C (-22 °F) once established, roughly USDA zone 4.
- When does Flat sea holly flower?
- From about July for 5–7 weeks (northern hemisphere; later in cold climates, earlier in warm ones).
- Is Flat sea holly poisonous to cats and dogs?
- For cats it is not well documented; for dogs not well documented; for people not well documented. No toxicity data found in ASPCA or standard poison references; spiny bracts can scratch skin.
- What grows well with Flat sea holly?
- There is no well-documented companion pairing for Flat sea holly. Group it with plants that like the same sun (full sun) and water (low).
Sources and evidence
Evidence grade C (C: plausible, mixed evidence).
- RHS Plant Finder, Royal Horticultural Society
- Missouri Botanical Garden Plant Finder, Missouri Botanical Garden
Notes and assumptions
- Typical garden-form values; cultivars and local conditions differ.
- Taproot resents division; best propagated by seed or root cuttings. Needs sharp drainage.
Reference values for planning, not horticultural, veterinary or medical advice. Varieties, soils and local climates differ: check with a local nursery or extension service.
Related plants
- Carrot Daucus carota subsp. sativus
- Parsley Petroselinum crispum
- Celery Apium graveolens
- Coriander (cilantro) Coriandrum sativum
- Dill Anethum graveolens
- Parsnip Pastinaca sativa
- Celeriac Apium graveolens var. rapaceum
- Florence fennel Foeniculum vulgare var. azoricum