GARDENING: Poison hemlock and wild parsnip in bloom - beware

Credit: Contributed

Credit: Contributed

A few weeks ago I wrote a column about poison hemlock and that it was time to spray with herbicide if you wanted to control the spread. Today, I am writing about it again because it’s in full bloom and you see it everywhere.

I want to continue to raise the awareness of this plant and its movement into the landscape. I am seeing it quite a bit in home landscapes, where the seeds have come from nearby ditches, roadsides, and fields.

Poison hemlock, Conium maculatum, has continued its spread around the Miami Valley. Most confuse it with Queen Anne’s lace, a plant in the same family with similar blooms. However, poison hemlock blooms now while Queen Anne’s lace blooms later in the summer.

While you drive, bike, or walk around our area, you can see this green plant with white blooms along roadsides, in ditches and fields, and even in the landscape. I have observed this plant in hayfields, and this is quite bothersome.

This biennial weed is blooming while the first-year seedlings are hiding on the ground, waiting to bloom next year. The white blooms are flat-topped and the tell-tale identifying factor for poison hemlock are the purplish streaks or spots on the green stem.

This plant is highly toxic to mammals and can cause respiratory failure and death. All parts of the plant are toxic with the roots more than the stems and leaves.

The toxins enter the body by ingestion and the sap enters through the eyes or nose or even a cut in the skin. Handling the plant and then rubbing your nose or eyes could be problematic.

If you are removing this by hand, wear protective eye and body cover as well as gloves. Wash thoroughly after working around it.

The best time to control poison hemlock was when I wrote the first article, at the early stages of growth. Now, the most important thing is to eliminate it from the landscape before it goes to seed and spreads.

I have been working on eliminating patches in my landscape that have escaped from the field next door.

Look around, almost all that white flower that is around four to six and even eight foot tall is likely poison hemlock.

Another plant that is also a growing problem is wild parsnip and can usually be found growing with poison hemlock. I haven’t seen as much of this in my area (Clark County) as my colleague in Cincinnati, Joe Boggs, has seen.

The sap of wild parsnip can cause severe blisters when skin is exposed to the sun. Wild parsnip blooms are yellow.

Joe has been writing about poison hemlock for many years when he started seeing it in southern Ohio. My colleagues have been observing and writing about the spread. To learn more about this and wild parsnip, go to and search for poison hemlock.

Joe does a great job with the articles but also includes incredible photos. Be on the lookout for both plants. And be aware of the potential danger.

Pamela Corle-Bennett is the state master gardener volunteer coordinator and horticulture educator for Ohio State University Extension. Contact her by email at

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