To help identify poison hemlock in home gardens, public trails, parks, or roadsides, note its smooth, hollow stem with purple blotches.

Photo courtesy of Ben Legler

Barbara Faurot

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The Apiaceae, or carrot family, features root crops like carrots and parsnips, culinary herbs like dill, fennel, and parsley, and beneficial natives like biscuitroot and yarrow. But it also includes sketchy relatives that are invasive and harmful to people, pets, livestock, and crops. Some are seriously or even fatally toxic.

Both the beneficial and noxious members of the family share characteristics that can make identification tricky — small five-part flowers arranged in umbrella-shaped clusters, hollow stems, and alternate, often fern-like leaves. Given the risks, accurate identification is essential. 

Christine Heycke, WSU Extension Master Gardener and member of the Jefferson County Noxious Weed Control Board, shares some good advice: “Take time to do your detective work. In the carrot family, there are several members with toxic properties. So assume it’s toxic until you’re sure.” 

Let’s take a look at some identification clues for the worst offenders that are considered noxious weeds in Washington: giant hogweed, poison hemlock, wild chervil, and wild carrot or Queen Anne’s Lace. 

Giant hogweed (Heracleum mantegazzianum) is present but not yet widespread in our county. Sometimes called cartwheel flower, it can grow to 15 feet tall with hairy hollow stems 2-4 inches in diameter and purplish blotches. Small, white flowers are arranged in clusters, often two feet in diameter. Leaves are 2 to 5 feet wide with jagged edges. 

Giant hogweed is a public health hazard. The plant exudes a watery sap that causes extreme sun sensitivity. This can result in severe burns, blistering, and scarring. 

Poison hemlock (Conium maculatum), another unwanted carrot family member, is widespread in the county. It can grow up to 10 feet tall with smooth hollow stems and distinctive purple splotches. Small, white flowers grow in 4-inch clusters. Leaves are dark glossy green and fern-like. Leaves and stems have an unpleasant musty odor.

All parts of the poison hemlock plant are extremely toxic to people, pets, and livestock. Accidental poisonings and respiratory failure can occur if people mistake the plant for a culinary look-alike. Touching the plant can also result in skin irritation. 

Wild chervil, or cow parsley (Anthriscus sylvestris), has been spreading vigorously this year. It grows to 1 to 4 feet tall and has small, white flowers in umbrella-shaped clusters about 3 inches wide. Its distinguishing features are green stems that are ribbed or furrowed, hairy on the lower portion and smooth on the upper portions. Fern-like leaves are shiny and dark green. 

Wild chervil is not toxic to animals, but it spreads rapidly and threatens native plants, home gardens, and farms. It acts as a host for viral diseases that affect beneficial family members, including carrots, parsnips, and celery. 

Wild carrot, or Queen Anne’s Lace (Daucus carota), is also widespread. 

It reaches 1 to 4 feet tall, and all parts of the plant are covered with coarse, stiff hairs. Small, white flowers appear in flat-topped umbels 2 to
4 inches in diameter. The central flower is usually reddish-purple. Stems are hairy and ridged without purple spots. Leaves are fern-like with small, toothed leaflets. 

Wild carrot is mildly toxic. It can taint milk if ingested by dairy cows. Like giant hogweed, the plant exudes a sap that causes sun sensitivity, resulting in blisters or other skin irritations. Unintended hybridization with edible carrot varieties can cause poor seed production and damage carrot crops. 

In Washington, landowners are legally responsible for controlling noxious weeds. The county’s approach is to offer educational materials and advice on eradicating current outbreaks and preventing new infestations. 

When handling noxious weeds, wear protective clothing and gloves. Use knowledge of the weeds’ life cycle to deploy a variety of tools. Our examples are all biennial plants, so removing them during their first growth cycle, when leaves form rosettes, is a good place to start. 

When plants are blooming in their second year, cut and bag flower heads. Christine suggests that “with any weed, if you can only do one thing, remove the flower heads before they go to seed. If you catch it before it spreads, you’re actually doing a lot.” 

Plants can be dug out at any time, removing all the root stock. Efforts may be most effective on dry, sunny mornings to maximize drought stress on plant or root fragments that remain in the soil. Avoid weed-whacking or mowing, which can spread the seeds. 

Research varies on whether composting effectively kills toxic weed seeds. So it’s safest to bag all parts of the plants and discard them in the household trash. Never burn toxic weeds to avoid releasing harmful toxins into the air. 

Cover bare soil after removing the weeds. Options include adding several inches of coarse organic mulch or planting cover crops, vigorous ground covers, or hearty natives. For large infestations, covering the area with black plastic sheeting for a season can help prevent seed germination. 

Herbicides are not a “silver bullet” — a combination of tools is most effective. If herbicides are used, directions should be carefully followed and risks should be considered, including vapor drift, physical drift, and unintended damage to desirable plants. 

The county’s Noxious Weed Control Board offers fact sheets with detailed photos of control options. Visit their website at co.jefferson.wa.us/195/Noxious-Weed-Control-Board. The state’s Noxious Weed Control Board is also an excellent resource, nwcb.wa.gov. 

The Master Gardener Plant Clinic offers live Zoom sessions to answer home gardening questions from noon to 2 p.m. Thursdays through September. Sign up or submit a question at extension.wsu.edu/jefferson/gardening-2/plant-clinic. 

(Barbara Faurot is a Jefferson County Master Gardener and Master Pruner, working with other volunteers who serve as community educators in gardening and environmental stewardship.)