@Vazgen - It doesn't seem to be a reliable glitch. Not sure exactly why that is, but I'd try quitting the game, reloading, and trying again. From reading a few comments online, it sounds like some people had to reboot several times before getting it to work. Some people also reported that it seemed to work better if you dropped multiple items. Maybe try dropping a few pieces of miscellaneous equipment along with the root/poison?
Sorry for not replying directly to you, but the comment thread seems to have reached the max length.