Poison Hemlock | Keweenaw Invasive Species Management Area (KISMA)

Conium maculatum

Characteristics

Poison hemlock, a biennial in the Apiaceae family, is an invasive herbaceous plant that prefers moist, shaded habitats subject to frequent disturbance but can be found in a range of habitats ranging from open fields to roadsides. Identifying features include:

basal rosette first year
grows to heights of 3-8 feet after the first year
stems are green with purple spots, glabrous, hollow, and without hair
leaves are triangular (8-16 inches), lacy, fern-like; leaf veins end at tips of teeth
small, white flowers occur in umbrella like clusters from June-August (more rounded than native species such as Queen Anne’s lace)

Note: As the name suggests, the poison hemlock is indeed poisonous. In fact, all parts of the plant are toxic and can be lethal to both humans and animals if ingested.

For more information visit Midwest Invasive Species Information Network (MISIN).

poison hemlock leaves — Triangular, fern-like leaves of poison hemlock

Image credit: Illinois Wildflowers

poison hemlock flowers — The white umbrella-like flowers of a mature poison hemlock

Image credit: Sigrid Resh

poison hemlock at the quincy ruins — Poison hemlock at the Quincy mine ruins

Image credit: Sigrid Resh

poison hemlock on edge of woods — Poison hemlock infestation on the edge of a field - notice the white flower clusters

Image credit: Sigrid Resh

KISMA Management Practices

Present within the Keweenaw, poison hemlock poses many ecological threats such as reducing quality wildlife forage, species diversity, and degradation of wildlife habitat. Currently, KISMA is managing populations around the Quincy Mine Dryhouse ruins in Hancock. Due to its toxicity, poison hemlock management can be problematic if done without caution.

wear protective clothing - pants, long sleeve shirts, gloves, and potentially a mask
when working with smaller populations, hand pulling with gloves is a viable option
when working with larger infestations, mowing or weed whipping is suggested, although repeated cuts - one early season before flowers bloom and one late season - will be needed to suppress the plant
after removal, ensure proper disposal through bagging/piling as the plant will remain toxic to humans and animals even after it is killed

Note: Like many other invasives, early detection and management of small populations is key to poison hemlock control. Because of the plant’s ability to produce a large seed bank, complete eradication will require several years of continued management and monitoring. Furthermore, management practices that target the plant's roots such as hand pulling are preferred, but not necessary as poison hemlock can only reproduce through seed production via its flowers.

Native Alternatives

If you do happen to remove poison hemlock on your property, it is never a bad idea to plant some natives in its absence! Since poison hemlock prefers disturbed sites with ample sunshine, it would be best to use natives that would also grow well in those conditions. A few great options would be native goldenrod (Solidago spp.), sunflowers (Helianthus spp.), wild lupine (Lupinus perennis), and native asters (Asteraceae family). These species grow well in meadows or field edges, and they also promote wildlife diversity.