Master Gardener: Setting the Record Straight to Poison Hemlock | Home & Garden

You’re right. News sometimes seems to take on a life of its own, especially on social media, and poison hemlock seems to be one of those topics in Tulsa right now.

The first thing you should know is that poison hemlock is poisonous. Most of the toxins are found in the seed, lower stem, and roots. In any case, you should not take it as it can lead to respiratory paralysis, coma and death if not treated quickly.

It is a threat to livestock and wildlife. Pigs are most at risk, but so are cattle, horses, sheep and goats. Livestock should not graze infested pastures in early spring when this plant is an early, green forage crop. However, livestock are more likely to encounter poison hemlock in contaminated hay.

One of the challenges is that poison hemlock is similar to wild carrot (Queen Anne’s lace) and cow parsnip. Each of these plants produces small, white flowers, so it would be easy to confuse them from afar. One way to identify poison hemlock is that its stalk has purple spots. In contrast, the wild carrot has a hairy stalk and the cow parsnip has a ribbed stalk. None of their stems have a purple on them, so that’s a key identifier. Poison hemlock also has a cat urine odor that becomes apparent in the summer.

Poison hemlock prefers a moist, shady spot to grow and is often found along streams or ditches. From there it can spread to adjacent areas.

A challenge in eliminating this plant is that the seeds can remain viable in the soil for three years, so any attempt to control poison hemlock will be a multi-year process rather than a single and completed one. Full control is expected to take three to six years if a tiered approach is used.

Because some people get a rash from handling poison hemlock, you should always wear protective gear when handling this weed. A mask wouldn’t be a bad idea either.

Mowing is a good strategy because mowing stresses the plant and reduces its ability to absorb nutrients. Herbicides such as 2,4-D or dicamba are effective against poison hemlock. Since these seeds remain germinable in the soil for up to three years, this will also be a multi-year process.

So be aware, look for purple on the stems and mostly stay away. Much luck!

You can get answers to all of your gardening questions by calling the Tulsa Master Gardeners Help Line at 918-746-3701, stopping by our Diagnostic Center at 4116 E. 15th St., or emailing us at mg@tulsamastergardeners.org .

Watch the Tulsa King teaser from Paramount+