“I’ve always been amazed by the state of most flyerboxes. (…) Some haven’t been filled in years. Yet, there they are: everywhere in the city (…) taking up valuable sidewalk space. (…) For whatever reason, a great many of them offer nothing but an empty box. But that offers a great opportunity for some people! (…) The boxes makes a perfect platform for planters – and with them you can guerrilla garden almost anywhere in the inhospitable concrete city! Best of all, it leaves the sides open for writers and artists.”
Earlier Posterchild filled flowerboxes with celosia plants and erected them on telephone poles around Kensington Market in Toronto. I strongly recommend you to start following this guy on Twitter!