There are 2 that are widely known: sun cheat and money cheat. You can cheat this game with Cheat Engine.
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Use cheat engine.
you can't add cheats on plant vs zombies but you can type on the screen the normal cheats like daisies,future etc.
There is a list of the various codes you can use on Chewy Central.
TrickeDout Pinata Daisies Sunny Days Tohot Future Mustache
plants vs zombies
Plants vs. Zombies happened in 2009.
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If you have Windows 7 you have Plants vs. Zombies for Free