Originally Posted by
bubby8ball
tested and confirmed, but it looks like you don't even have to do anything with the upgrade. Just pick each herb, not looting anything from them and kill any mobs that spawn and loot their corpses. After you have picked each plant, they will disappear after about 30-35 seconds, but then respawn after another 20 seconds, and you can wash, rinse, repeat after that.
It appears that if you loot anything from the herbs, even just a seed from one of them, and don't loot the other herbs, after they disappear, they will not respawn, so make sure not to loot anything from any of the plants.