PopCap Games is now distributing digital coupons which can be redeemed between October 30 and November 10.
They are being handed out in batches, with the idea being that people can give them to trick or treaters instead of sweets. The promotion is backed by the American Dental Association.
"Before you go get tons of sweets for trick-or-treaters, check this out: you can give away Plants vs. Zombies for Mac or PC. And you won't pay a cent," read a statement from PopCap.
"Now through Halloween, you can team up with PopCap and the American Dental Association to redefine what a Halloween 'treat' can be... by giving fun instead of candy."
Plants vs. Zombies, a popular tower defence game, was released on PC in 2009. It has been ported to numerous systems, including the Xbox 360, PS3, iOS, Android and handhelds.
Electronic Arts will publish an official sequel to the game in 2013.
> Read our review of Plants vs. Zombies for iPhone
> Electronic Arts purchases PopCap for $750 million
Gallery - view images of the Plants vs. Zombies merchandise range below: