How far apart should I plant Alexanders (horse parsley)?

About 50 cm (20 in) apart, centre to centre. A mature plant spreads 50 cm–1 m (20 in–3.3 ft).

Does Alexanders (horse parsley) need full sun?

Part sun to part shade: at least 4 hours of direct sun a day.

How much water does Alexanders (horse parsley) need?

Moderate water. Drought tolerance is low and waterlogging tolerance none.

How cold-hardy is Alexanders (horse parsley)?

It tolerates about -12 °C (10 °F) once established, roughly USDA zone 8. As a biennial it is usually planted out after the last frost and flowers in its second year.

When does Alexanders (horse parsley) flower?

About 43–57 weeks after planting, for 4–6 weeks.

Is Alexanders (horse parsley) poisonous to cats and dogs?

For cats it is not known to be toxic; for dogs not known to be toxic; for people not known to be toxic. Not poisonous, but it is an umbellifer: be sure of identification if foraging (hemlock water-dropwort grows in similar places).

What grows well with Alexanders (horse parsley)?

There is no well-documented companion pairing for Alexanders (horse parsley). Group it with plants that like the same sun (part sun to part shade) and water (moderate).

Alexanders (horse parsley) Smyrnium olusatrum

Alexanders (horse parsley) (Smyrnium olusatrum) is a biennial vegetable in the Apiaceae family, native to Mediterranean region; long naturalised along coasts of Britain and western Europe. It grows 50 cm–1.5 m (20 in–4.9 ft) tall and 50 cm–1 m (20 in–3.3 ft) wide, wants part sun to part shade and moderate water, and is hardy to about -12 °C (10 °F). Space plants about 50 cm (20 in) apart.

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Alexanders (horse parsley) at a glance

Type	Biennial vegetable
Family	Apiaceae
Mature height	50 cm–1.5 m (20 in–4.9 ft)
Mature spread	50 cm–1 m (20 in–3.3 ft)
Spacing	50 cm (20 in) centre to centre
Sun	Part sun to part shade, at least 4 h of direct sun a day
Water	Moderate; drought tolerance low, waterlogging tolerance none
Soil pH	6–8
Cold hardiness	About -12 °C (10 °F) once established (roughly USDA zone 8)
Heat stress	Likely above about 30 °C (86 °F)
Flowering	about 43–57 weeks after planting, for 4–6 weeks
Days to maturity	About 365 days from planting
Wind tolerance	Moderate
Pollinator value	High
Edible	Yes: stems, leaves, flower buds, seeds (peppery)
Native to	Mediterranean region; long naturalised along coasts of Britain and western Europe
Common in gardens of	🇬🇧 United Kingdom, 🇮🇪 Ireland, 🇫🇷 France, 🇮🇹 Italy, 🇬🇷 Greece, 🇪🇸 Spain

Is Alexanders (horse parsley) toxic?

People: not known to be toxic
Cats: not known to be toxic
Dogs: not known to be toxic

Not poisonous, but it is an umbellifer: be sure of identification if foraging (hemlock water-dropwort grows in similar places).

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 Alexanders (horse parsley)

No well-documented helpful pairing. Group it with plants that like part sun to part shade and moderate water.

Questions about Alexanders (horse parsley)

How far apart should I plant Alexanders (horse parsley)?: About 50 cm (20 in) apart, centre to centre. A mature plant spreads 50 cm–1 m (20 in–3.3 ft).
Does Alexanders (horse parsley) need full sun?: Part sun to part shade: at least 4 hours of direct sun a day.
How much water does Alexanders (horse parsley) need?: Moderate water. Drought tolerance is low and waterlogging tolerance none.
How cold-hardy is Alexanders (horse parsley)?: It tolerates about -12 °C (10 °F) once established, roughly USDA zone 8. As a biennial it is usually planted out after the last frost and flowers in its second year.
When does Alexanders (horse parsley) flower?: About 43–57 weeks after planting, for 4–6 weeks.
Is Alexanders (horse parsley) poisonous to cats and dogs?: For cats it is not known to be toxic; for dogs not known to be toxic; for people not known to be toxic. Not poisonous, but it is an umbellifer: be sure of identification if foraging (hemlock water-dropwort grows in similar places).
What grows well with Alexanders (horse parsley)?: There is no well-documented companion pairing for Alexanders (horse parsley). Group it with plants that like the same sun (part sun to part shade) and water (moderate).

Sources and evidence

Evidence grade B (B: extension service or peer-reviewed).

Plants of the World Online (taxonomy, native range), Royal Botanic Gardens, Kew
Plants For A Future database, PFAF
Wildflowers and meadows, Plantlife (UK)

Notes and assumptions

Glossy, celery-like leaves in winter and yellow-green umbels in early spring, loved by early insects. The pot-herb eaten in Europe before celery replaced it; often said to have been brought to Britain by the Romans (likely but unproven). Self-seeds freely.

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