You can first attempt this in the alchemy shop in the town of Gorhart. Head downstairs and approach the alchemy lab and activate it. From here, select experiment from the options. You will be shown a list of all the reagants you own. Hopefully you have successfully harvested a few by this point in the game. If not, head back out into the world and walk up and activate (press X) on any of the plants you find. You can play around with ingredients and make all types of potions from here.
Personally I had a few Black Cohosh and Embereyes. Combine the two of them for a minor health potion, and this trophy.
Black Cohosh (2 needed) and Embereyes (1 needed).