Symbolism, Imagery, Allegory
More specifically, one garden. In a book that takes place almost entirely in the living room of one house, it's a major news item when somebody goes out in the garden. Throughout most of the book, only the terrorists are allowed to stroll around the grounds of the VP's mansion, so references to the garden emphasize how the hostages are trapped inside. But when hostages actually go out into the garden, the symbols really start flying fast and furious.
Some things the garden symbolizes:
Gen and Carmen's Relationship
Early in Gen's crush on Carmen, we see him staring out the window, trying to catch a glimpse of her while somebody else is trying to talk to him (6.69-73). The fact that she's allowed outside and he isn't emphasizes the distance between them as terrorist and hostage. When later on Carmen secretly takes Gen out into the garden late at night, it symbolizes their growing romance (8.195-204).
The part of the garden they're in is beautiful, wild, and secret—kind of like their relationship. But it's also a garden that's unlikely to stay wild. It's overgrown because of the hostage crisis, but usually it would be a neatly manicured space—which it'll be again if/when the crisis ends. Does that underline the sense that Gen and Carmen's life together will also be "weeded" (you know what we mean) when the crisis ends? You betcha.
The Growth of Community (see what we did there?)
The hostages don't get to go outside until chapter 9, when the book is almost over. But when they do, it's a sign that the slowly growing community among terrorists and hostages is becoming more and more real.
Once everyone's in the garden, the two sides really start being hard to tell apart. Terrorists and hostages play soccer together (10.18), so they have fun and exercise in their community.
Some of the hostages start doing gardening tasks, so they're contributing to the growth of the place they live together (you can't get more symbolic than that, Shmoopers!) (9.134).
Um. Eden?
Can't get much more paradise-y than a garden with springtime coming.
This ties into the growth of community stuff, but it also shows how idyllic and even utopian that community is. They're all digging it so much, but we just know it can't last.
Like how Oscar Mendoza and Ruben Iglesias invite Ishmael to be a long-term part of their lives, post-hostage stuff. That's imagining a brighter future, but also an impossible one. And when Ishmael starts helping Ruben garden (10.115-116), he shows how deeply the two communities have meshed, plus a view of unity that just may be a bit over-idealistic.
Let's not forget everyone's out enjoying the sun, like high schoolers who just got out of class for the summer. Can't get much closer to paradise than that.
That all makes it a lot more tragic when the government forces start shooting people in the garden in Chapter 10 (10.119). You can't have Eden without getting kicked out of it.