Toxic Plants Rear their Ugly Flower Heads
Authors Thomas deHaas
Published on June 9, 2025
It’s that time of year in Northwest Ohio that two toxic plants are coming into flower. Poison Hemlock and Wild Parsnip are both in full flower but are toxic in different ways.
Poison Hemlock is a biennial that flowers or bolts in the second year if its life cycle.
It is flowering prolifically along freeway right of ways and can be seen in patches driving down the highway.
Its leaves are fine and lacy, and the stem of the plant is smooth, greenish white with pink blotches. The flower heads are white.
I wrote an article about this time two years ago titled “I Spy…..Poison Hemlock”: https://bygl.osu.edu/node/2157
Poison Hemlock has sap that is toxic and can cause heart problems. So weed whacking or brush hogging patches can release sap and cause health problems as Joe Boggs points out in the article “Poison Hemlock is No Joke”: https://bygl.osu.edu/node/2111
It’s too late to control Poison Hemlock now since it has already set seed for next year. But if you map where you have patches growing, next spring you can spray the rosettes in the spring before they bolt and go to flower as Curtis Young points out in his March article from 2024 “Now is a Fine Time to Scout for Poison Hemlock”: https://bygl.osu.edu/node/2313
So, what can you do ‘NOW?’ Map out infestations of Poison Hemlock. These patches are often found on road right of ways, banks of stream beds, and fence rows along farm fields.
The key is to know where they are and spray next spring. The seeds have already formed so spraying now is a waste of time and material.
What about Wild Parsnip?
It does not stand out like Poison Hemlock, but it is still there and very dangerous if it comes in contact with your skin. Wild Parsnip has a yellow flower head similar to Queen Ann’s Lace but is in flower now.
The leaves look similar to celery leaves. The stalk looks different as well.
Also, a biennial, it flowers in the second year of its life cycle. As Joe Boggs points out in “Poison Hemlock and Wild Parsnip: TOO LATE!”, Wild Parsnip can cause serious skin burns: https://bygl.osu.edu/node/2356
In the above article, Joe also points out that an application of herbicide in the second year of growth in the spring for Wild Parsnip is an effective control.
Again, mapping patches of Wild Parsnip will help you target herbicide applications next year. Whatever you do, don’t pull Wild Parsnip!
Be aware, the battle to control both may take a number of years since seeds can germinate years after deposited on the soil.
But now is the perfect time to scout for both.