G.T. plants trees to keep memories alive.

G.T. actually plants trees to commemorate specific events related to his loved ones.  He takes Hope out back where his grove of trees thrives, telling her, "come on over here and meet my memories".  In the grove, there is a large oak that he had planted twenty-five years earlier when he had gotten married.  Nearly, there is a smaller tree, a dogwood, planted four years earlier, when his beloved wife had died.  G.T.'s trees also include three "white birches...for the three grocery stores (his) parents owned", and a "Japanese maple (which) went in the ground eight years (earlier) when Al opened his church".  G.T. introduces Hope to the trees like old friends, and he shares with her the special memories about the important people in his life that each tree evokes.

G.T. tells Hope specifically his reason for planting the trees.  He says,

"I like thinking they'll be here long after I'm gone.  All those fine memories pushing up to the sky" (Chapter 8).

G.T. has a special affinity for trees that seems to go even beyond his act of planting them to give his memories immortality.  G.T. also uses tree metaphors to help him express his understanding of life, as when he carries little baby Anastasia out into the grove and tells her about the mustard seed, "one of the smallest seeds in the tree family, but...one of the mightiest" (Chapter 11), and when he grafts a cut branch onto another tree to symbolize his new relationship with Hope after she agrees to be adopted by him, illustrating that they "didn't start from the same tree, but (they're) going to grow together like (they) did" (Chapter 19).