Fountain
At the end of each of your turns, you may choose a Pile and turn it to its GRASS side.
If the chosen Pile is already GRASS, this doesn't do anything.
You can choose a Pile in another player's YARD, but that kind of move is likely to help you lose the game.
Cards stay on a Pile when it turns from DIRT to GRASS (and vice versa.)
This action triggers at the end of your turn, regardless of whether you're Home or Away.