Control where particles show up on static mesh with Niagara

I have a static mesh that is meant to be the terrain and I want to spawn particle mesh foliage on it. I’m doing it this way because I want to change the foliage over time in various ways, including making it go away. All as the player watches.

So my question is: I can use Niagara to put the mesh particles on the static mesh terrain object, but I don’t know how to control what different foliage meshes go where. Anyone have any thoughts on this?