Not scorn, but for clarity and accuracy....
The plants will help to scatter upper mid and high frequencies somewhat. They will not diffuse. There is a big difference. Diffusion provides even and random redistribution in both space and time. Plants will not do this evenly and in both dimensions. Also, you'd want to address both 'sides' evenly so if you're going to go this way, you'd want to have 2 plants that are identical and set up as mirror imaged of each other if in the front or rear of the room.
Bryan