Games : What is the chance of getting a zen garden plant?

In PvZ, once you unlock the Zen Garden, there is a chance you can get a plant, or chocolate (used to feed plants or Stinky the snail). What I want to know is; What is that chance?

And now that there are different copies on different consoles, is there a difference between them? I.e. Console vs. PC vs. Android/Apple?