My suggestion: almost never blend between textures, there are very few situations where it is appropriate. More importantly, blending can kill the visual style of your game - a clean, minimal palette almost always looks better (with distinctive borders between colors or color gradients). A better solution is to give each tile type a layering priority - i.e. grass tile edges overlap dirt, sand, etc. Rather than blending, disintegrate the edges appropriately (i.e. grass gets less dense as it goes towards a barren tile, sand is dispersed as it goes over a rock surface, etc).
For example, look at the grass in this image: