Need Help - 2D Flat Ground Materials

Hello everybody, I need some help designing my 2d Game. My style of graphics is flat up and down much like the early Civilizations, with the characters moving up, down, left, and right, across a “ground” which makes up the background; just like pokemon. The difficulty I am having is texturing the ground and adding to the background. At first I made a plane which faced the camera directly for a grass texture, which worked fine until I wanted to add stone, and realized that you can’t assign multiple materials to different faces of a mesh like you can in blender and maya. Then I decided to make a mine-craft like system of stacking square sprites of textures next to one another, but this very quickly became too large and too messy. How can I add a background with seamlessly changing grounds without making one huge sprite for the entire game’s world? Is it possible to texture half of a plane with stone and the other half grass? I really cannot proceed with my game without finding a solution to this key problem. I hope I have made myself clear.

2D games are based on depth sorting,Use different quad/planes for different graphic elements with diffrent depth.

Example

First create a quad for the ground which has the ground grass texture.Above that create another quad/plane for the rock or stone not on the same depth to avoid Z fighting.

Refer the unity 2D shooting tutorial

you can project decals to add extra detail to your ground, here free asset that can help you with this: Unity Asset Store - The Best Assets for Game Making

you can also use texture blending to mix several textures into one. this require some knowledge in shaders, or you can use asset from asset store for this.