A Blend Shader That Uses Vertex Information

So i need to make a basic blend shader which works a bit more complex than a normal blend shader.

I have a mesh with n x n vertices. Let's say each vertex has information assigned to it such as type of terrain (ie. grass, dirt, snow).

So a 3x3 set of vertices might have data like this:

...

grass snow snow

grass grass dirt

grass dirt dirt

...

Based on these values, the mesh should render each vertex with the given texture, and if 2 adjacent vertices have differing data, then it will gradient from one texture to another.

I made a basic version of this but unfortunately it doesn't take into consideration vertices so when i play around with it, the entire mesh material will fade into the next material.

Here is the shader code: http://pastebin.ca/3730042

Can anyone point me in the right direction?