The name – poisonous hemlock – says it all. This highly poisonous plant grows wild in El Paso County. It is included in the Colorado Noxious Weed List as a List C plant.
A noxious weed is a non-native plant designated by the Colorado Department of Agriculture as harmful to agricultural or horticultural crops, natural habitats or ecosystems, humans or livestock. Although management of List C species is not mandatory, poisonous hemlock should be eradicated from your landscape due to plant toxicity and the possibility of accidental ingestion by humans, pets, or livestock. All parts of the plant are poisonous.
One of the factors contributing to accidental ingestion is the fact that poison hemlock (Conium maculatum) belongs to the carrot / parsley family (Apiaceae). They are biennial plants and the first year plants resemble parsley or carrots. Just slicing up what you think is parsley for your salad could lead to illness or death. In the second year of growth, the white flowers borne on the umbels strikingly resemble wild carrots, also known as Queen Anne’s lace. You should never harvest an “edible plant” from the wild unless you are absolutely certain of the identity and safety of that plant. Children may find the bamboo structure of the flowering plants attractive for play, perhaps making “snorkels or whistles” from the hollow stems; be sure to teach them not to play with plants that are not approved by adults.
The poisoned hemlock, 4 to 8 feet tall, has fern leaves and white flower umbels. Since there are other similar plants, confirm your identification by looking for purplish spots and colouration on the stem. There is another species of hemlock native to Colorado, the water hemlock (Cicuta douglassii), which is more poisonous. It is not a noxious weed in Colorado as it is a native plant.
Management of these plants can be accomplished either by elimination – they are fairly easy to dig up in the spring – or by the application of broad-spectrum herbicides. If the plant is in flower or forming seeds, be careful not to scatter the seeds if you are removing the plants by digging or weeding them. When working with these plants, be careful to avoid skin contact by wearing gloves, long sleeves, and long pants. Although contact with the skin is not as dangerous as ingestion, it can cause a rash.
Here are two resources on identifying and managing these plants:
Submit your gardening questions to [email protected] The in-person assistance service, 17 N. Spruce St., will be open from 9 a.m. to noon and 1 to 4 p.m. on Wednesdays. Find Colorado Master Gardeners – El Paso County on Facebook.