If you want grass and plants to cover your landscape, then Landscape Grass Types are your best bet.
Essentially you can tell the engine which foliage meshes you want to place on each layer of your landscape (I’m assuming you have layer set up on your landscape already, but if not, I think these videos show how to do that too).
These videos should be a good starting point (although, disclaimer, I haven’t watched either of them all the way through, but they look fine at a glance)
