Q&A: Is this giant hogweed or poison hemlock?

poison hemlock

Poison hemlock can be mistaken for giant hogweed

Q: I think I might have giant hogweed on my property, or maybe it is poison hemlock. How can I tell for sure?

A: Giant hogweed (Heracleum mantegazzianum) was found recently in Clarke County, Virginia, and it has raised awareness and concern about the plant – and rightfully so. The plant produces toxic sap that can cause very severe skin inflammation. We have received a lot of questions about it lately.

poison hemlock

Poison hemlock Photo: E. Nibali

What you have here is NOT giant hogweed. It is poison hemlock (Conium maculatum), which is much more common. The ferny foliage makes it possible to distinguish it from giant hogweed.

All parts of poison hemlock are toxic too. If you’re removing the plant from your landscape, treat it like you would poison ivy. Wear gloves and a long-sleeved shirt when you handle it. If you’re mowing the plants, wear a face mask as well.

With regard to concerns about giant hogweed, be aware that there are several other plants that look very similar to it. In addition to poison hemlock, there is common cow-parsnip, angelica, wild parsnip, wild chervil, Queen Anne’s lace, and golden Alexanders. Some of these plants also contain toxins, but none are as potent as giant hogweed.

In Maryland, invasive giant hogweed has been found in Garrett, Baltimore, and Harford Counties, where it has been controlled. It is possible to find giant hogweed elsewhere in the state, but the chances are much greater that you will encounter one of the look-alike plants.

If you think you see giant hogweed, avoid touching it. Take photos (particularly of the flowers and stems, if possible) and look at this identification guide online. If you are still unsure about the plant’s identity, send clear digital photos to our Ask an Expert service and we will help you.

Giant hogweed is a federally regulated noxious weed. Suspected sightings of it will be reported to the Maryland Department of Agriculture Plant Protection Division.

Additional Resources

By Christa K. Carignan, Coordinator, University of Maryland Extension Home & Garden Information Center

Have a plant or pest question? University of Maryland Extension’s experts have answers! Send your questions and photos to Ask an Expert.

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