How do you get the doom shroom in your garden in Plants vs Zombies for the xbox 360?

To obtain the Doom Shroom in Plants vs. Zombies on Xbox 360, you need to progress through Adventure Mode until you reach Level 5-10. After completing this level, the Doom Shroom will unlock and become available for purchase in your Zen Garden. You can then plant it in your garden to enjoy its powerful effects against zombies.