To me the garden represents the necessary process of growth. Much like the growth cycle of a plant, a tree, or a fish in a pond, it symbolizes the boy's desire to mature and to enter the mysterious world of adulthood. Similarly, the woman teacher, finding herself in an unpleasant and pressuring environment desires to be young again; to revert to the glory and the blurred comfort of childhood... that's why she's so drawn to the boy - he has opened her eyes to her past youth. To me, the teacher is the boy's gateway to a world of potential, whereas the boy is the teacher's refuge. Therefore, the garden as a embodiment of growth and maturation is the perfect middleground for them to meet.