Like most of Garrison Keillor's stories about his fictional hometown, Lake Wobegon, "How the Crab Apple Grew" is rooted in the small events and little details that make up memory and nostalgia. The setting is Lake Wobegon, a small town in Minnesota where "All the women are strong, all the men are good-looking, and all the children are above average." The setting is deliberately rose-colored, with only small hurts and injuries and many, many happy memories; the idea is to remember how growing up was so much better than the present, because everything was simpler and people were more honest. This piece speaks to the themes of family and heartbreak, and determination; Harold Diener loses his love, Marlys, because of his youthful stupidity, and gets her back because of his own hard work (and, to be fair, the public humiliation of his rival). The crab apple tree in the back yard is a symbol of both his love and the families that grow and prosper in small towns:
He watered it and tended it and, more than that, he came out late at night and bent down and said, "GROW, GROW, GROW." The graft held, it grew, and one year it was interesting and the next it was impressive and then wonderful and finally it was magnificent... A backyard is a novel about us, and when we sit there on a summer day, we hear the dialogue and see the characters.
(Keillor, "How the Crab Apple Grew," faculty.chemeketa.edu)
In a more urban setting, the story would not have as much impact, because the themes of family and agriculture (moral mushrooms, mud, the tree itself) would have no importance to urban people. In a small town, working the land was still of major importance to the culture, and so the tree becomes a symbol of family growth and, as a graft, of marriage itself. Additionally, the small town rivalries shown here are not as passive-aggressive in urban environments, but instead often lead to violence; here, the rivalries are solved with panache and cultural understanding of one-upsmanship.