I've watched this stop carpenter ants all day. Cherry tree.
Upside-down plastic flower pot barriers work against carpenter ants because they disrupt the ants’ normal climbing and trail behavior. Carpenter ants prefer textured vertical surfaces, edges, and established pheromone trails. The smooth inverted plastic forces them to transition from bark to a difficult upside-down surface with little traction and no clear trail path. Even though ants can technically walk upside down, larger carpenter ants struggle on smooth plastic over longer distances, especially around outward overhangs and lips. Once enough ants fail to cross consistently, the pheromone trail weakens and the colony often abandons the route entirely. Environmental factors like dust, heat, condensation, and surface flexibility can further reduce grip and effectiveness.