Hey Yuki, maybe this could give you an idea of how to approach this: https://cgcookie.com/tutorial/realistic-particle-dirt-in-blender
You could also model the pebbles and make them Rigid Bodies and then ‘drop’ them in the (upper part of the) pot.
Both methods are quite ‘expensive’ and it depends on the scale of the scene and how you are going to use it (I wouldn’t use this in a game for instance).
Your idea with a plane and textures is great, but you would probably need real Displacement (meaning a lot of polygons) on the plane to get some nice depth.
