In a sense, Bastion was a game about growth—over the course of the game, The Kid would bring back items and characters to the Bastion, which allowed it to grow and flourish. In a metaphorical sense, the Bastion was a sort of garden, growing over time.
As it turns out, the game's planting parallels were originally much more explicit. Talking at the Game Developers Conference, Supergiant Games designer Amir Rao talked about the original plan to make the game revolve around gardening—players would plant seeds to grow everything from weapon power-ups to character upgrades to new areas to explore.
As Rao described it, players would gather seeds in the real world and plant them in the bastion, which would cause plants to grow and give them power-ups.
Rao was talking at the "failure workshop" during the indie-centric part of the conference; several designers gave short talks about various failures they've had while working on games. And true to the spirit of the talk, the plants idea was a failure.
The plants didn't clearly communicate progress to the player. Rao offered the example of a "hammer tree" that grew new, better hammers—but what does that look like? How do you make it clear that this tree grows hammers? As cool as the idea was, Supergiant realized that it wasn't working, and flipped it back to the conventional approach—they used graphical menus. As he put it, the key with experimenting systems like that is knowing that if it's not working, you can always return to convention.
In a humorous touch, Rao shared a recording of Bastion's now-famous narrator Logan Cunningham improvising some dialogue about planting things. It seems like a bit that started out earnestly, conveying the focus on planting that Supergiant was going with… but it goes off the rails into improv-ville pretty quickly.
Find a pair of socks? Plant it.
Find a Milli Vanilli casette tape? Plant it.
Heh. I dunno, I would have enjoyed collecting and planting Terminator 2 laserdiscs. Maybe in Supergiant's next game...