Can plastic planters be 'aged' in the same way that clay/terracotta pots can with yogurt, beer, moss etc? Answered

Clay pots are really happy to grow all sorts of lichens and algae/moss. This is because they are porous and hold nutrients and water, as well as provide a surface for the little guys to grow on. I can't say from experience, but try roughing up the surface as fox says, then apply all sorts of moss-food. worst case scenario you'll have a dirty pot. Perhaps sew a burlap 'cone' the shape of the outside of the pot, then attaching that with hot glue. It's porrous, and should be happy to grow moss.