Yeah, Plant Lover trait took on an unexpected angle. Harvesting, flower arranging, eating, etc. can cause negative moodlets. As you are cutting/eating your friends.
I think we expected this to be like Sims 3 Green Thumb trait but better, instead they act like a PlantSim with communicating with plants and acting like plants are their kind/babies/friends/aka personifying plants.
I believe there is some lost in translation of previous installments' traits and Sims 4 traits. I believe Sim 4 wants to reinvent or do some traits different, and in some cases they did a nice job but in others they lack or are just confusing some players.
I accepted that Plant Lover trait works the way it does and either have a Sim act like a Plant caretaker and just avoid harvesting/cutting/uprooting/using plants or have them as a conflicted Sim over plants and plant activities—with their moodlet swings.