I’ve seen people posting about poison hemlock and am seeing a lot of contradictory information. What do I need to know about poison hemlock in Tulsa? MW

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

The first thing you should know is that yes, poison hemlock is poisonous. Most of the toxins are located in the seed, lower stem, and roots. Either way, you don’t want to ingest it because doing so can result in respiratory paralysis, coma, and death if not treated quickly.

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

One of the challenges is that poison hemlock looks similar to wild carrot (Queen Anne's lace) and cow parsnip. Each of these plants produce small, white flowers so it would be easy to confuse them from a distance. One way to identify poison hemlock is that it’s stem has purple spots. In contrast, wild carrot has a hairy stem and cow parsnip has a ribbed stem. Neither of their stems have any purple on them, so that is a key identifier. Poison hemlock also has a cat urine type smell that is evident during the summer.

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

One challenge with eliminating this plant is that their seeds can remain viable in the soil for 3 years, so any attempt to control poison hemlock is going to be a multi-year process rather than a one and done. Complete control will likely take 3 to 6 years using a multi-tiered approach.

Since some people break out in a rash by even touching poison hemlock, be sure to wear protective clothing at all times when working around this weed. A mask wouldn’t be a bad idea either.

Mowing is a good strategy since mowing will stress the plant and reduce its ability to intake nutrients. Just remember, this process could take several years. Herbicides such as 2,4-D or dicamba are effective against poison hemlock. Because those seeds remain viable in the ground for up to 3 years, this too will be a multi-year process.

So be aware, check for purple on the stems, and stay away for the most part. 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: Ansel Oommen, Bugwood.org