mix a noise texture with a normal to make patches I have a forest ground but I want to mix in a grass texture over that. I have tried but found no susses so far. 
My plane are to use a noise texture an after that put on a image texture on top.
Try to use MixRGB node for blending Color and Height images with Noise Texture then put result to Base color and Height inputs of Principled BSDF and Displacement node.