Poison hemlock is a biennial, herbaceous weed in the carrot family (Apiaceae). It is native to Europe and the Mediterranean but has naturalized in the United States and become problematic. It is highly toxic and can be fatal to people and livestock. Many states have listed it as a noxious weed. It grows 6 to 10 feet tall and 4 to 5 feet wide and quickly colonizes an area and displaces native plant species. Its white fleshy taproot has red spots and resembles a parsnip or carrot. The stems are hollow and have small purple spots. Showy white flowers look like umbrellas or like other members of the carrot family. The leaves of poison hemlock resemble parsley. The roots, leaves and stems have a foul odor when crushed. It is found growing in disturbed areas, at roadsides, along fences, on streambanks or in ditches. In early spring it emerges from the soil with a basal rosette of fine-textured ferny leaves. While it is usually a biennial, in ideal locations – full sun to partial shade and moist soils – it can be perennial. It reproduces by seeds which are dispersed by animals, machinery and clothing and persist in the soil for years, making eradication difficult. Insects, Diseases and Other Plant Problems: No significant problems.
Curated pairwise relationships between this plant and others in the library — who feeds
whom, who competes, who confuses the pests. Green reads as a good pairing, red as one to avoid.
No curated interactions recorded for this species yet.
Also noted by NC State
Related species the NC State Plant Toolbox flags for this plant — look-alikes to tell
apart, and plants that play a similar role in a planting. Ones we carry in the library are linked.
Full sun (6 or more hours of direct sunlight a day) | Partial Shade (Direct sunlight only part of the day, 2-6 hours)
Soil drainage
Moist
Mature size
Height: 6 ft. 0 in. - 10 ft. 0 in. | Width: 4 ft. 0 in. - 5 ft. 0 in.
Growth rate
Rapid
Maintenance
High
Canopy layer
4 - Herbaceous (3-15 ft)
Form & Appearance
Habit / form
Erect
Texture
Fine
Leaf color
Green
Leaf type
Compound (Pinnately , Bipinnately, Palmately)
Leaf shape
Deltoid; Ovate
Hairs present
No
Leaf detail
Large, 3-4 pinnately dissected, the leaflets broadly ovate to deltate very delicate and resemble parsley leaves with prominate veins on the underside. They clasp the stems at enlarged nodes.
Flower color
Pink; White
Flower value
Showy
Flower form
Umbel
Flower size
< 1 inch
Flower detail
Small, white 5 petaled, in terminal umbrella-like clusters with one purple flower in the center of the cluster. Flowers appear late summer.
Bloom time
Summer
Fruit color
Brown/Copper; Gray/Silver; Green
Fruit detail
Green ovoid to suborbicular compressed laterally and wavy ribbing on the surface. Each fruit contains a single seed, and the fruits are generally called "seeds." At maturity, fruits turn gray-brown. The fruits ("seeds") resemble those of anise.
HIGHLY TOXIC, MAY BE FATAL IF EATEN! Delivery by ingestion. Salivation, vomiting, diarrhea, muscular weakness, paralysis, nervousness, trembling, dilation of pupils, weak pulse, convulsions, coma. People with highly sensitive skin may experience contact dermatitis from handling this plant.