For more detail this asset from the Unity Asset Store: Click Here
This is a paid asset, but now you can download VolumeGrass for FREE, Please keep in mind this package is provided only for learning purposes or to be able to test before buying the product, NOT FOR COMMERCIAL PURPOSES.
VolumeGrass v1.5d
Volumetric Grass gives unlimited density of grass with no CPU overhead !
Forum & demos | Documentation PDF | Video
This is complete system for building volumetric grass that can be used on Unity4 Free (DX11 needs Pro license) and Unity5
Consists of grass mesh editor and a special shader that gives an illusion of grass being rendered “inside” the mesh volume.
Grass look is highly configurable, handles directional and spherical wind zones & proper intersections with other objects. You can make your own textures easily using built-in editor. For full feature guide refer to forum thread.
Package requires GPU with SM3.0. Mobile versions are on the roadmap (while shader works quite fast on current desktops). Unity4.5+ is highly recommended for shorter install time.