Adding grass on custom terrain

Unity Engine
1

Does 2018.3 has easier method to add grass on imported terrain?

So that you could paint with foliage brush on custom terrain rather on Unity terrain.

2

What’s a custom terrain? Is this a static mesh only or some 3rd party solution?

3

Static mesh

4

The grass, details and tree system have not been modified (yet)

5

I think what you’re looking for is Polybrush (Beta) from unity technologies in the asset store.
It’s free and offers Mesh Scattering - painting objects with a brush on any other object.
Haven’t had a look at in in quite a while so I don’t know how “beta” it’s functionality and stability currently is.