Poison Hemlock (Conium maculatum)

Poison Hemlock (Conium maculatum) Information

By Ronnie Dauber, Garden Guides Contributor Although Poison Hemlock is native to Europe, it has become widely spread across the northern United States and into Canada. It is most often displayed along roadsides, in ditches, on hiking trails and in field borders. The plant is attractive with its deep green leaves and white flower heads, but is extremely poisonous. It will cause toxic reactions if the volatile conium alkaloids are inhaled. It is fatal if the yellowy sap is taken internally. It is not considered an edible food for pasture animals; but if they consume it, the results will be death.

General Characteristics

The Poison Hemlock is a biennial that can grow to a height of between two and ten feet. Its dark green, fern-like leaves are divided 3 or 4 times and look similar to the leaves of a carrot. The plant produces basal rosettes the first year and erect, ridged and hollow, shiny stems with distinct purple spots the second year. The white flowers, which bloom in the second year, are about one and a half to two and a half inch compound umbels, forming clusters of smaller flowers within. The roots are solid, thick white taproots. The main identifying characteristic that separates this as a poisonous plant is the display of purple spots on the stems. The Poisonous Hemlock has been mistaken for wild carrots and Queen Anne's Lace.

Growing Conditions

The plants grow well in wet, shaded areas, pastures and wetlands. They grow along streams, rivers, ravines, ditches or in any soil that is constantly moist and in the sunlight; but they can also easily adapt to drier and shadier locations.

Cultivation and Care

The Poisonous Hemlock does not require any maintenance to grow and should be eradicated upon sight.

Weed Control Techniques

The most effective means of control is to eliminate the Poison Hemlock plants in the early spring before they produce seeds. This can be done manually by digging up the plants, being careful to wear protective garments to avoid skin contact, or by mowing down or cutting back the plants with a weed-eater. Follow this with mulching and replanting the area with desired plants. In highly infested areas, it may be necessary to spray the plants in the spring with glyphosate (Roundup) and remove them in the fall when the plants have fully absorbed the herbicide. If there are other plants around the hemlock, which could suffer from the herbicide, it may be necessary to spray each hemlock plant individually.

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