Having played with them on the PBE, plants have to be your worst idea yet, Riot.

They're completely random, which means that even though you can see them coming, you have no control over them. They force the player to play around them, which in theory is the point, but they fail miserably at being an interesting thing to plan plays around. The fact is, whoever has more AA range wins control of the plant. This massively fucks over melee champions. Range inequalites aside, never in my games have I thought: "Oh look, that player used that plant to outplay the other guy." Every time, without fail, all that happens is to everyone involved is a feeling of frustration and a cheapened sense of achievement, because a large portion of what affected the play is something that randomly showed up, and no one had control over. They're gimmicky, obnoxious, and a chore, because most of the time the right play is to get rid of them before the fight starts. That's all they'll ever be, and I pray with all my heart that you guys come to realize how bad of an idea they are.