I can't really tell because the player is moving around a lot but it looks to me like those plants are 3D plane objects with a mesh distort animation on them.
You can get a similar effect by adjusting the height and angle of individual plant leaves with a sin/cos oscillation. Just be smart about where you put your hotspots. They should go at the base of the leaf where it connects to the plant, or the base of the plant where it connects to the ground. When playing your demo it looked to me like the hotspots on your plants were closer to the center, which made the bases wobble back and forth.
I would only use that level of separate-leaf detail on very foreground plants, though. Having full plants and flowers in the mid and background should suffice, and only put composite leaf-by-leaf plants in the foreground.
Also, you can change the period and range of the Sine behavior so if you want the plants to do something like bend to one side in the wind you could bump up their angle period so they "flutter," as well as skewing them in the wind direction.
Ultimately though you might find you have more control over how they move by doing this with solely with events, rather than having Sine behavior on them. And you don't really need a shader.