In Plants vs. Zombies, players must protect their homes from zombies by planting various types of plants that will attack and defend against them. The game uses a grid-based layout, with the player's house on the left and the zombies advancing from the right side of the screen. At the beginning of each level, the player is given a certain number of suns, which is the currency used to grow different types of plants. Suns can be collected by tapping on sunflowers, which produce suns over time, or by breaking certain pots on the game board. Plants that can be grown include pea shooters that shoot peas at zombies, potato mines that explode when a zombie steps on them, and cherry bombs that can destroy a large group of zombies at once. Each plant has unique abilities and costs, so players must choose carefully which plants to use in order to effectively defend their homes.

There are several types of zombies, including basic zombies, soccer zombies with protective gear, and even zombies riding on zombie machines (ice remodelers). Some zombies can also climb over obstacles or fly over plants, adding an extra layer of challenge for players. Players defend their homes against wave after wave of zombies by successfully defending them against the increasing difficulty in each level. The game also features mini-games and puzzles, such as survival mode, where players must hold out as long as possible against an endless horde of zombies. As players progress through the game, they earn coins that can be used to purchase upgrades for their plants, such as faster firing or increased damage. They can also acquire new plants and unlock new game modes.

The game also features a wide range of environments, including backyards, rooftops and swimming pools. Each environment has unique challenges and obstacles, such as a swimming pool that requires players to use aquatic plants to fend off zombie dolphins. one of Plants vs. Zombies' most unique features is its sense of humor. The game is filled with wacky characters, from dancing zombies to angry-looking sunflowers, and features a variety of humorous animations and sound effects.