We've got a theory: the Gibb Street garden in Seedfolks is sort of like a time machine. Seriously, all you have to do is shovel some dirt or plant some seeds in the ground, and you might find yourself transported to a past experience. Think about it: for Amir, the garden has him remembering his family's Persian rug. And for Tío Juan, working on the garden is like being with "old friends" (4.9). But don't forget that lots of our characters have some tragic stories in their pasts. So while the garden may provide pleasant recollections for some characters, others still have some tough memories to work through.
It's good to remember the past. The garden helps lots of characters to connect with their memories, and that's a good thing.
It's best to forget the past. Seedfolks argues that the garden allows characters to start fresh and move on.