You can unlock new plants by progressing through the game's levels. Each level or world may introduce new plants that you can use in your defense against zombies.

Sun is the currency in Plants vs. Zombies™ needed to plant new plants. You earn sun by planting sunflowers or by receiving it from the sun that falls from the sky.

To strategize effectively, place sun-producing plants in the back rows to generate sun and defensive plants in front. Use explosive plants to handle large groups of zombies.

You'll encounter various zombie types, including regular zombies, conehead zombies, and buckethead zombies, each with unique defenses and abilities. Adapt your strategy to counter their strengths.

To defeat Gargantuars, use high-damage plants like the Catapult or Cherry Bomb, and employ strategies that slow them down, such as using Ice-Shroom or Spikeweed to prevent advance. Follow these steps:
1. Place high-damage plants as close to the Gargantuar as possible.
2. Use plants that slow them down to give your damage-dealers more time.
3. Combine different attack plants for maximum effect.
4. Be ready to replace plants quickly as they get destroyed.