Behind our house the city has just finished a section of sewer pipeline. It was super deep - maybe 20' - and they did not save the topsoil. After the subsoil was spread out over the 50' wide area they seeded with grass and rye but it is the worst concrete-subsoil stuff I have ever seen, and the not even contractor grass seed is surviving. I feel like this long, open area on ignored municipal property could be turned into something useful (with perhaps a little guerrilla gardening) such as pollinator habitat. Any suggestions for something that would grow in (almost) concrete that could also take some flooding?