Petunias growing in the cracks is so neat! Last year I was pulling stuff growing out of the cracks that turned out to be catnip. I have a planter of catnip that re-seeds every year and some seeds must have germinated in the cracks, but they were way bigger than my catnip in the planter.
I'm growing Lantana in pots this year and I'm going to try to bring in doors and see if I can't keep them alive for the winter.