The city of Chicago has planted "four raggedy excuses" for trees in front of the house on Mango Street. Esperanza draws strength from these trees. Like her, she says, they do not belong in this place; nevertheless, "[t]hey teach" her by showing her how to be strong, by digging their roots deep. By growing down, they also grow up-as Esperanza is struggling to do.
Esperanza makes the symbolism of the four trees explicit for her audience in this vignette. The trees symbolize strength. They are living, and growing, despite their location in a place where they do not naturally belong. Like the trees, Esperanza is, figuratively speaking, stuck in concrete-the urban asphalt of her Mango Street neighborhood. Like the trees, she has been putting down "ferocious roots" in this place, roots that will enable her to grow and even, ultimately, to leave Mango Street without leaving it entirely behind (see "Mango Says Goodbye Sometimes").
The House on Mango Street: Novel Summary: Four Skinny Trees