Tree Food is a special fertilizer used to grow the Tree of Wisdom. It costs $2500 per bag and can be purchased at Crazy Dave's Twiddydinkies. It can be fed to the Tree of Wisdom one bag at a time, making it one foot taller. In order to grow it to 100 feet, the player will need to spend $237,500. So, in order to grow it to 1000 feet, the player will need to spend $2,487,500.
Each time the player feeds the Tree of Wisdom, it will give the player valuable information until it grows out of the screen. At this point, it will then just grow one foot per bag. It also gives the player a random new cheat at set intervals as it gets taller. The given cheats sometimes add random effects to the zombies that the player fights on mini-games and in Adventure Mode that can only be used if the player has already grown the Tree of Wisdom to the required height. These codes only work on the regular Zombie, Conehead Zombie, and Buckethead Zombie. The player can only acquire 10 bags at a time.
When the Tree of Wisdom reaches 1000 feet, it will stop giving the player wisdom, but the player can still grow it much taller. However, the tree will still give the player some flavor text that does not mean anything.
There is a limit to how tall the player can grow the Tree of Wisdom. 2,147,483,647 feet is the maximum height, feeding it any more will turn it back into a sapling (with its minimum height) which will not grow again unless the player feeds it for another 2,147,483,647 times. This is because of an integer overflow.
Tree Food is not in the iOS version of Plants vs. Zombies, since there is no Tree of Wisdom available. Instead, bacon is used to spend the player's money on (even though it does nothing in the game and is used to just waste the player's money).