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Poison Hemlock

From time to time, we identify Poison Hemlock on publicly accessible sites that we own and maintain. Most notably at Holywell Fish Ponds.

We always endeavour to take appropriate action to remove Poison Hemlock. It may take up to five years to remove, owing to it readily self seeding.

Where we implement control measures to eradicate this weed, signage will be in place on site to make members of the public aware.

We advise the public to keep away from these localised areas within our sites. Otherwise, the sites remain open and available for public enjoyment.

Please read our advice below to keep yourself, others and animals safe from Poison Hemlock.

About Poison Hemlock

Hemlock is one of the most poisonous plants to humans and animals. It is highly toxic to humans and animals and can be fatal. Do not touch or ingest any part of the plant.

Hemlock poisoning occurs after ingesting any part of the plant. Both the growing and cut dried plant are poisonous. Its seeds, flowers, leaves, roots etc contain toxic alkaloids. These toxic alkaloids can be fatal to humans and animals, even in small amounts. Even touching the plant can cause a skin reaction.

There is no antidote for Hemlock poisoning.

Spring growth with previous summer's dead stem in the background

How to identify Poison Hemlock

Hemlock is a member of the carrot family. It looks similar to Cow Parsley with its big white flowers, tall slender stem and green leaves. However, there are some identifiable differences that are worth noting:

Pink / red / purple spotting on the stems of the plant. Key identifying feature.
  • Hemlock has a smooth, green, hollow stem which is usually spotted or streaked with red, purple or pink on the top and lower half of the stem.
  • The plant grows tall, usually 1.5 to 2.5 metres (5 to 8 feet), but could reach heights of 3.5 metres (12 feet).
  • Hemlock produces umbrella-like clusters of white or cream flowers. The plant usually flowers in summer, not during spring or autumn. The non-flowering form has bright green leaves and the red, purple or pink spotting or streaking feature on the stem that the tall, flowering plant has.
  • The central stem has sets of two opposite branches with triangular feather-like leaves along these. The central stem itself is hairless and hollow. The plant has a long whitish taproot.
  • Unlike similar looking edibles, Hemlock has a distinctive unpleasant musty smell if the plant is damaged.
  • Hemlock can look very similar to other plants including carrots, parsnips, chervil and cow parsley.
  • Hemlock has a two-year lifecycle (growing from seed to fruition and then dying). However, the seeds can lay dormant and remain viable for three to five years.
Dead hemlock stem with green growth at base.

Please note we don't have any photos of Hemlock in flower yet due to the time of year. For further photos of Hemlock, please see the Wildlife Trust website.

Symptoms of Hemlock poisoning

Those with Hemlock poisoning will display symptoms after 30 minutes and up to 3 hours, depending on the extent of contact or the amount ingested.

When touched, the plant can generate a painful rash or painful burning on the eyes if contact is made here.

Ingesting any part of the plant can lead to poisoning. This affects the nervous and respiratory systems and can lead to respiratory failure.

Symptoms include:

  • Trembling
  • Burning sensation in digestive tract
  • Increased salivation
  • Dilated pupils
  • Muscle pain and weakness
  • Decreased heart rate
  • Loss of speech
  • Convulsions
  • Unconsciousness

Seek medical attention immediately if you experience any symptoms or think you have come into contact with Poison Hemlock.

If possible, take a sample of the plant for identification if it is safe for you to do so. Use plastic gloves or a bag to avoid direct contact. If not, take some photographs.

Do not try and make the patient sick. Help them to remain calm.

The NHS website has a webpage about Poisoning.

Report instances of Poison Hemlock on public land

If you notice Poison Hemlock growing on any public land owned or maintained by us, please call 01733 747474 to report. The phone line is open Monday to Friday, 9am to 5pm.