Can I grow this in my garden?

It is strongly discouraged due to its extreme toxicity and invasive nature.

How do I identify it?

Look for purple blotches on the smooth, hollow stems and fern like leaves.

Plant guide

Poison hemlock.

Conium maculatum

Pronounced KOH-nee-um mack-yoo-LAY-tum

Also known as Carrot-fern, Deadly Hemlock, Fool's-parsley

Poison hemlock is a highly toxic biennial plant often found in disturbed areas and along roadsides. It is famous for its historical use as a lethal poison. You should avoid touching or ingesting this plant entirely.

At a glance

Care level: Easy
Plant type: Biennial herbaceous plant
Light: Full sun to partial shade
Indoor light: Direct sun
Water: Every 3 to 7 days
Mature size: 6 to 10 feet
Growth rate: Fast
Hardiness: USDA 4 to 9
Bloom time: Late spring to mid summer

Care

This plant is considered a dangerous invasive weed and should not be cultivated in home gardens. If you find it on your property, wear gloves and protective clothing to remove it before it sets seed. Watch for skin irritation after any contact with the foliage.

Watering: It prefers consistently moist soil but can tolerate short dry spells.
Feeding: It does not require fertilization as it thrives in most soil conditions.
Pruning: Remove flower heads before they produce seeds to prevent further spread.
Repotting: It is not recommended to keep this plant in containers due to its size and toxicity.
Soil: Moist, fertile, well drained soil
Soil pH: 6.0 to 8.0
Temperature: -34 to 30°C
Humidity: 40 to 70%
Drought tolerance: Moderate

Safety

People: All parts of this plant contain potent alkaloids that cause respiratory failure and death upon ingestion.
Pets: This plant is extremely poisonous to both cats and dogs if ingested.
Children: This plant is highly dangerous to children due to its attractive appearance and extreme toxicity if touched or eaten.
Contact allergens: Handling the foliage can cause skin irritation or dermatitis in sensitive individuals.
Airborne allergens: The pollen can trigger allergic reactions in some people.
Edibility: This plant is extremely poisonous and can be fatal if ingested, even in small amounts.

How to identify it

Purple blotches on smooth stems
Finely divided fern like leaves
Small white flowers in umbels
Taproot resembles a parsnip

Height: 1 to 2.5m
Spread: 0.3 to 0.6m
Leaves: bright green, deciduous
Flowers: white, 0.2 to 0.5cm
Fruit: brown, Late summer

Problems to watch for

AphidsCommon
Powdery MildewUncommon
Root RotUncommon
RustUncommon

By symptom

Plant problems by symptom

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Growing it

Propagation: seed
When to plant: spring, autumn

Do not plant this near any edible crops due to the high risk of accidental ingestion.

Similar species

Wild Carrot · It looks similar but lacks the purple spots on the stem.

Science

Family: Apiaceae
Genus: Conium
Order: Apiales
Class: Magnoliopsida
Native range: Europe and North Africa
Conservation: It is considered an invasive weed in many regions and is often subject to control measures.

It thrives in disturbed soils, roadsides, and damp areas where it can outcompete native vegetation.

Value to wildlife: nectar source
Pollinators: bees, butterflies, beetles
Uses: botanical study, historical interest

Through the year

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Flowering

Fruiting

Foliage

Ecological indicators

Salinity: 2/9
Soil reaction: 6/9
Light: 6/9
Temperature: 5/9
Moisture: 6/9
Nutrients: 7/9

Taxonomy resolved against GBIF.

Questions people ask

Can I grow this in my garden?: It is strongly discouraged due to its extreme toxicity and invasive nature.
How do I identify it?: Look for purple blotches on the smooth, hollow stems and fern like leaves.

Where the name comes from

The name Conium comes from the Greek word for hemlock, while maculatum refers to the spotted appearance of the stems.

Good to know

It is a member of the carrot family.
The stems often have purple spots.
It is a biennial, meaning it grows leaves the first year and flowers the second.

Also in

Plants toxic to cats and dogs

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This guide was generated with AI on September 26, 2026 and checked against GBIF taxonomy. It is general information, not horticultural or veterinary advice. Read about how we build these guides.