I know I'm late to the gardening party, but I just got my first golden apple. The first I've noticed anyway. It was from a standalone apple tree, but the fruit landed next to a random potato plant my current mayor planted when she was "helping" me garden as a child. The apple and potato were directly next to each other,no full squares in between.
I have the rabbit's foot, but I've had since the second or third day of playing. I'm on day ten or so now. So, to me, it seems random.