Hi Jennifer !

An important question because, unfortunately Poison Hemlock is readily found in Ohio. And, this is a good time of year to ask that question.

First, I have to ask you to make sure that it is Poison Hemlock (Conium maculatum) that you have on your property. Poison Hemlock's appearance is very similar to that of  Queen Anne's Lace (Daucus carota, often called wild carrot) and some other plants.  Poison Hemlock differs from them in appearance in its hairy, purple-speckled, hollow stems. The other plants have smooth, solid stems without speckling. Queen Anne's Lace and other similar plants can be left to grow, or removed without the use of herbicides, if you so choose.

Assuming that you've made certain that you do have Poison Hemlock, if the amounts are small, you can remove Poison Hemlock mechanically (digging the plants up) as well. However,  you will need to be very careful about your personal protective gear ! You will need long pants, closed-toe shoes, long sleeves, heavy duty gloves and even mask and goggles to prevent any sap reaching your face, legs and arms. Remember that Poison Hemlock is toxic to both humans and animals. Keep pets and livestock away, and children of course. If you do dig up the plants, do NOT compost or burn.  Place the plants in a heavy duty bag, seal and put in the trash.  

For herbicide spraying of larger groups of Poison Hemlock, you will need the same protective gear listed in the above paragraph, plus any other items that might be recommended by the nonselective herbicide that you use. Please carefully read the instructions on the herbicide container for your safety and that of the environment. 

If at any time you start feeling sick - vomiting/diarrhea, difficulty breathing, confusion, changes in pupil size or heart rate, call 911 for treatment, as hemlock poisoning can be fatal. 

As far as timing of any herbicide application (or mechanical removal), the present time (February) and early Spring (March) are good times to manage Poison Hemlock.  Poison Hemlock's rosettes can remain green throughout much of the winter and early spring when other types of foliage are generally brown, making them easy to spot at this time. Most of the Poison Hemlock plants that you see now are probably second year plants (Poison Hemlock plants are biennial - they live a 2-year cycle) and you want to destroy them before their central stem arises in early to mid-summer in order to prevent flowering and seeding.  You may need to re-spray in the Fall to catch some of the young plants that you have not caught in early Spring because they weren't readily visible or identified. Check your sprayed area in about a month to make sure that the plants are destroyed and re-spray if not.   

I hope this helps ! Good luck on Poison Hemlock control and feel free to contact us with any further questions. 

You can check out https://u.osu.edu/sheep/2012/04/17/identify-and-control-poison-hemlock/ for further information.