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Poison hemlock

Quick facts

Poison hemlock is an invasive species on the Prohibited Eradicate List. The plant must be destroyed and transportation, propagation, or sale of these plants is prohibited.

  • Poison hemlock is found near railroad tracks, rivers, ditches, field edges, farms and bike paths.
  • Poison hemlock should be reported. 
  • The Minnesota Department of Agriculture monitors this invasive species. Please report any poison hemlock you spot at Arrest the Pest.

WARNING: Poison hemlock can be deadly to humans and livestock if ingested. All plant parts are highly toxic. Protective clothing and gloves must be worn when working in an infestation.

poison hemlock plant with white blossoms with blue background

Poison hemlock (Conium maculatum) is an invasive plant native to Europe and North Africa.

It is highly toxic and can be fatal to humans and livestock.

Poison hemlock requires considerable sunlight to flourish and is found often near railways, rivers, ditches, field edges, farms and bike paths. It is a biennial plant (having a two year life cycle), and is unlikely to grow in very shady areas or places that are frequently mowed.

Close-up of red spotted poison hemlock stem
Poison hemlock stem

How to identify poison hemlock

  • Biennial herbaceous plant that starts out as a low-growing rosette and matures into a tall flowering stalk, up to eight feet.
  • Highly poisonous.

Stem

  • Smooth, hollow, light green stems with purple spots.
  • May appear ridged due to veins.

Leaves

  • Alternate, generally triangular in form.
  • Doubly or triply pinnately compound, up to 18 inches long by 12 inches wide, with dark green leaves.
  • Leaflets are fern-like, deeply divided and typically twice as long as wide.
  • Basal leaves tend to be larger and have longer petioles than upper stem leaves.
  • Petiole to stem attachments are covered by a sheath.
poison hemlock plant with defined fern looking leaves
Poison hemlock

Flowers

  • White with five small petals, cluster in an umbrella shape at the tips of branches.
  • Umbels can be two to three inches across.
  • Blooms May to August.

Seeds

  • Round, ridged seeds are produced in abundant quantities.
  • Two seeds per capsule that split at maturity.
  • Each seed is flattened on one side and lined with vertical, wavy ribs.

Roots

  • Taproot resembles a small white carrot or parsnip, but is deadly when eaten.

Human health impacts

All parts of poison hemlock (roots, stems, leaves and seeds) are extremely toxic to humans and livestock when ingested. Small amounts can be deadly.

This toxin impacts the nervous system causing trembling, salivation, lack of coordination, dilated pupils, weak pulse, respiratory paralysis, coma and death. Extra care should be taken to wear protective clothing and eyewear before working with or exposure to poison hemlock.

Common look-alikes

Many plants are often mistaken for poison hemlock, or vice-versa. Use this printable poison hemlock lookalikes chart (PDF) or the list below to determine if you have found poison hemlock.

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Reporting poison hemlock

If you believe you have found poison hemlock, contact Arrest the Pest and send a picture of the purple spots on the stem, a leaf, and the specific location of the plant. We ask that you report the plant so that we can track the extent of the invasion and need for future control across the state.

Natural resource and other land management professionals should use the GLEDN app to report poison hemlock plants.

Once you have determined it is poison hemlock decide if you or a professional will treat the plants on your property.

Management

It is highly recommended that you call a professional to handle this plant. However, if you choose to manage poison hemlock yourself, be sure to wear gloves and other protective clothing including eye wear. Shower afterwards to be sure you have no toxic sap on your skin, and launder your clothes.

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Disposal

We recommend you call a professional to safely dispose of the poison plants. 

  • Do not compost the plants as the seed and poison will stay viable into the future and more plants will reappear later. 
  • Do not burn the plants as this may release the toxin.

If your garbage services accept poisonous plants (as does Dodge, Fillmore, Olmsted and Winona counties) then place the plants in plastic bags and put them in the garbage. The plastic bags will protect the health of the people who handle the garbage even after leaving your property.

If your county does not accept poisonous plants, then bury the plants, flowers and seed heads in an area that will remain undisturbed.

Emergency, livestock, and other resources

For suspected ingestion call the Minnesota Poison Control Center 1-800-222-1222

Angela Gupta, Amy Rager and Megan M. Weber, Extension educators

Reviewed in 2020

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