Flowers on the sidewalk

On the walk I take several times a week, I recently saw these flowers growing on or over the sidewalk.
It makes me think of "flower power." Do you like to see flowers or weeds growing in a crack in cement, or flowing and crowding onto the sidewalk? The first photo is pink marguerites, the second yellow poppies and the third white poppies. Can you tell from the photo that the pink marguerites almost completely cover the sidewalk? The white poppies are growing where I can't see any dirt; just a crack between a metal pole and the cement sidewalk. I wonder, if people were no longer here, how long would it take for nature to cover all the cement?