We’re starting to see poison hemlock and Queen Anne’s Lace popping up so let’s talk about how to identify these two plants and what you should know about them.

The first thing you should pick up from the name “poison hemlock” is the term “poison” in the name. It’s not just a nickname. While most of the toxins in the plant are in the seeds, lower stems, and roots, you don’t want to ingest any part of the plant since doing so can cause respiratory paralysis, coma, and death. Yes, that’s a pretty strong penalty for snacking on a plant.

However, the primary threat from this plant is to wildlife and livestock. Pigs are the ones most at risk, but it is also potentially dangerous to goats, sheep, horses, and cattle. If you have this plant in an area where these animals might graze, they should not be allowed to eat poison hemlock. Poison hemlock can sometimes be found in contaminated hay.

One of the primary challenges with poison hemlock is that it looks very similar to wild carrot (aka Queen Anne’s Lace) and cow parsnip. From a distance, these plants are easily confused since they produce small white flowers. To positively identify poison hemlock, look at the stem. The stem of poison hemlock has purple spots while the wild carrot’s stem is hairy. Cow parsnip has a ribbed stem. Neither of these two have the distinctive purple spots found on poison hemlock. Poison hemlock also has a rather distinctive smell in the summer, similar to cat urine.

Another indicator to help identify these plants is that poison hemlock prefers a shady, moist place to grow, oftentimes located along streams or ditches. However, from that location it can spread to nearby areas.

If you find your have an outcropping of poison hemlock where you don’t want it, eliminating it can be challenging since their seeds can remain viable in the soil for up to 3 years. Because of this, control of poison hemlock will require a multi-tiered approach lasting potentially 3 to 6 years.

You can start by mowing the plant. Mowing will stress the plant and inhibit its ability to take in nutrients. Herbicides such as 2, 4-D or dicamba are effective when used on poison hemlock. Just remember, there are probably some of those long-lasting seeds in the ground below, so you’re going to have to stay after it to eliminate it completely.

When working in the same area as poison hemlock, it’s a good idea to wear protective clothing and a mask since even touching this plant can cause some people to break out in a rash.

So, remember, purple on the stem, stay away from them. Good luck.

You can get answers to all your gardening questions by calling the Tulsa Master Gardeners Help Line at 918-746-3701, dropping by our Diagnostic Center at 4116 E. 15th Street, or by emailing us at mg@tulsamastergardeners.org. Photo: Chris Evans, University of Illinois, Bugwood.org