Moss and sand? Hmmmmm
Its what is underneath the top layer that counts, have you verified what other types of plants are growing in the same area/conditions, weed can do well in many different environments but make sure its not too damp, I have always planted mine in local soil with no amending and they have always been monsters, they just suck up whatever they can find, the surrounding vegetation will give you the best clue, if youve got lots of annual lush weeds in the same are you will be fine! In the summer damp soil can be an advantage in hot weather but come fall it could give you early root rot, best of luck!
