These two plants are poisonous and have made headway in the Miami Valley in the last few years. Many misidentify them and mistake them for Queen Anne’s lace. While similar, they are considered dangerous to have around.
Poison hemlock (Conicum maculatum) and wild parsnip (Pastinaca sativa) are both non-native invasive weeds in the carrot family (hence the reason for mistaken identity).
They are biennials, which means they take two years to complete their life cycle. The first year, they are vegetative and grow in a rosette form. Plants that have this habit have leaves that are circular arrangement of leaves, growing low to the ground.
They spend the season producing carbohydrates for a very robust root system. They overwinter as roots and the next season they enter the flowering stage. The stems shoot up, flowers develop, and they go to seed and die.
They produce copious amounts of seeds to ensure the species continues. Seeds may stay in the ground for up to four years. You may see a stand of them with both flowering and vegetative plants mixed.
Why should you eliminate these plants? Because they are both toxic and you don’t want them in the landscape.
Poison hemlock was what killed Socrates. All parts of the plant are toxic and if ingested can cause respiratory failure and death for mammals.
However, you don’t necessarily have to ingest them to be poisoned. Handling them could lead to sap on the skin. This sap can be transferred to the eyes, nose, other membranes or a cut and can lead to poisoning.
Wild parsnip is an interesting plant that causes phytophotodermatitis. The sap, when on the skin and exposed to the sun, can cause severe blisters and often a redness that can last for several months.
These plants bloom in May, with poison hemlock having white blooms and wild parsnip having yellow blooms. I tend to see more stands of poison hemlock than wild parsnip in the Miami Valley, though we do have both.
Don’t mistake this for Queen Anne’s lace, which blooms in late July and August. Learn to identify these plants to eliminate them.
Poison hemlock has distinctive purple blotches on the stems and wild parsnip has leaves that resemble celery. Go to bygl.osu.edu and search for poison hemlock to find several articles and photos on both plants as well as control options.
This is the best time to spray with herbicides. There is little other vegetation present; they are easy to spot and are the most susceptible to herbicides. Once they get to the flowering stage, herbicides are not as effective.
If you decide to pull them or handle them, wear proper protective clothing and gloves, and keep the sap off your skin.
Pamela Corle-Bennett is the state master gardener volunteer coordinator and horticulture educator for Ohio State University Extension. Contact her by email at bennett.27@osu.edu.
About the Author