Poison Hemlock

General

Native to Europe, western Asia and North Africa.
Highly aggressive and toxic plant that invades pastures and riparian areas displacing valuable forage species and native plants.
Acutely toxic to humans and animals, with symptoms appearing 20 minutes to 3 hours after ingestion. All parts of the plant are poisonous and even the dead canes remain toxic.
Ingestion is the main danger but it is also toxic through the skin and respiratory system.
Plants have a disagreeable musky smell, especially when leaves are crushed.

Identification

Biennial that forms a low growing rosette the first year and the second year bolts up to 10 feet tall, with small white flowers with five petals that occur in 4-8 inch umbrellas shaped clusters.
Blooms during May through August in Washington
Leaves are triangular, toothed, finely divided and alternately arranged; gradually reducing in size going up the stem.
Stems are hollow and hairless with purple to purplish-red spotting or blotches.
Long taproot, pale yellow in color, with numerous lateral roots may be mistaken for a pale carrot.
Plants die back after setting seed, leaving upright dead stems that can remain into winter.

Photos

Habitat

Colonizes disturbed sites, including roadsides, vacant lots and construction sites. Also found in gardens, backyards, open fields, meadows, and stream and river banks.
Prefers moist soil, but can grow in almost any conditions.

Reproduction and Spread

Reproduces solely by seed. Each plant produces up to 40,000 seeds. Seeds germinate almost immediately, but can remain viable for 2-4 years.
Seeds are dispersed by erosion, animals, rain and human activity.

Control

Use caution when removing poison-hemlock. Make sure to use PPE including gloves, long sleeves, long pants, eye protection and possibly a mask.
It is best to remove plants in the rosette stage before they bolt, if this is not possible cut just below the flower or seed heads and dispose of them in the trash.
Small infestations can be effectively hand-pulled or dug up.
When removing a large, mature plant, cut the stem to allow access to the root mass. Use a hand tool such as a shovel or Pulaski to dig up the root and remove as much as possible; small fragments left in soil will usually not resprout.
Mowing once will not eradicate poison-hemlock and plants will quickly grow back. Mowing can prevent seed production if repeated multiple times however caution must be taken to avoid release of volatile oils from the plants, especially during hot days.
- Sheet mulching can be effective following mowing. Use biodegradable plant fabric, burlap or cardboard and apply 6-8 inches of mulch.
Do not burn plant material as toxins can be released into the air.

Herbicide Control