Question about texturing Hex Terrain (XPS Foam)

This is my first build, I've got my hex terrain cut out and I'm wondering about the best way to create some textures on the sides. I'm going with grass/gravel trees etc. for the tops but I want the edges to look like rock. should I try to cut a pattern into the edges or maybe glue on some sand to make a texture before I paint? I'm not looking for anything too fancy (difficult), just something besides smooth edges. I have a wire foam cutter, knives etc.