To be specific, you'll have three options for donating to the cause with straight Facebook Credits, rather than Farm Cash, but each of the three prices earns you the Rainbow Chard permit. You can give $5, $10 or $25 to the cause, and in addition to being allowed to plant the new crop, you'll also receive a collectible gift, but what that prize is specifically wasn't made clear.
As for the crop itself, it comes with some decent stats, being available to plant for 15 coins, and going for 100 coins once it's ready to harvest four hours later. You'll earn two experience points for each square planted. The Rainbow Chard can never wither, regardless of how long you leave it alone, so at least you don't have to worry about the short growth time popping up as a negative later on when you can't login "in time."
All of the proceeds from this charity event go straight to the Edible Schoolyard Project, so keep that in mind if that helps you find the inspiration to donate. As usual, doing so is entirely voluntary, but at least it will give you a new goal to reach for if you've already mastered everything else in the game. That's something, right?
Will you donate any money to the Edible Schoolyard Project, or are you fine skipping this limited edition crop in your game? Which dollar amount did you donate to the cause? Sound off in the comments.