Public advisory (PDF) | Treatment proposal (PDF) | Map of sightings | Photos/videos

What is Poison Hemlock?

  • Poison Hemlock, an invasive plant, is fatally toxic to humans and animals if ingested. It can also cause harm if inhaled during mowing or trimming.

Where does it grow?

  • PH can now be found in almost every US state
  • It commonly occurs in dense stands along roadsides, stream banks, irrigation ditches, field margins, waste areas, riparian woodlands, and open floodplains.

How will I recognize it?

  • See the identification guide above. 
  • Look for jagged, triangular leaves, blotchy purple stems, and lace-like white flowers.
  • Plants can range from a few inches tall to 8-10 feet.
  • It tends to grow in moist environments with good sun exposure.

What should I do if I see it?

  • Avoid it – do not cut, mow or burn poison hemlock.
  • Report it – take a photo and send it to <>. (If possible, describe the specific location, area of coverage, and plant height.)
  • Warn neighbors and visitors in the area.
  • Even dead plants remain toxic for years.

What if I accidentally touch it?

  • Generally, physical contact with poison hemlock will not cause a rash.
  • If you (or your pet) accidentally ingest poison hemlock, seek immediate medical attention.

Where is it in Closter?

  • While not entirely new to Closter, PH has spread recently due to favorable climate conditions and uncontrolled growth in hidden areas. 
  • Thus far, PH has been sighted in multiple locations around Closter Nature Center and the Closter DPW composting site.

How will Closter address this?

  • Eradicating Poison Hemlock is a difficult, multi-year process requiring careful controls and application of herbicides. To avoid continued spread, quick action is required.
  • Closter Nature Center, Closter Environmental Commission, Closter DPW, and others seek to develop a public awareness campaign and a mitigation strategy.
  • If herbicides must be employed, they must be applied prior to flowering in June.

How can I help?

  • Report any sightings.
  • Share this information with residents, visitors, school and scout groups, landscapers, etc.
  • Follow the Environmental Commission’s info page at
  • If you wish to join a PH cleanup team as a volunteer, contact us at <>


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Last modified: May 23, 2024

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