Roses of Sharon produce flowers all through the summer and fall, and the flowers each produce a pod of seeds like this. Thus the bush spreads in the city. Its favorite habitat is along fences and among hedges, where the lawn mower won’t get it; in fact, it is very good at taking over entire hedges gradually, until the hedge is nothing but Rose of Sharon. To be fair to the plant, Rose of Sharon makes a very good hedge with very attractive flowers, so you may just want to let it take over.