- For the Chinese version of the level, see Lost City - Day 21 (Chinese version).
- For the Chinese version of this level before the v1.8 update, see Lost City - Day 21 (Chinese version: pre-1.8).
Lost City - Day 21 is the twenty-first level of Lost City in Plants vs. Zombies 2. It is a Locked and Loaded level. This is the first time Toadstool is showcased in Lost City. There are ten Gold Tiles in this level; there are two of them in each of the first five columns. After completing this level, the player receives a money bag.
- This level is relatively easy as the player, even without typical sun-producing plants, still has three sun sources: Toadstool, Sun Bean, and Gold Tiles.
- Stallia's ability of being able to slow multiple zombies and having no sun cost allows it to be planted anytime when recharged, and lets the player to focus more on planting Toadstools.
- The small number next to the zombie icon means that zombie will always appear in that lane, with 1 being the topmost lane and 5 being the bottommost one.
|Waves||Non-dynamic zombies||Ambush zombies||Note(s)|
|4||4||None||100% Plant Food|
|6||1 2 5 4 2||None||First flag; 400%/7 Plant Food|
|8||1 3 5||None||100% Plant Food|
|10||4 5||None||600%/7 Plant Food|
|12||3 4 1 2 5||None||Final flag; 600%/7 Plant Food|
- The player should keep planting Toadstools because it is the only way to kill zombies other than lawn mowers, Power Ups or boosted Sun Bean (which is not recommended).
- For the first few minutes of the battle, planting Stallias on Gold Tiles should earn the player a good amount of sun to plant Toadstools.
- The player should only use Plant Food on Toadstools during final wave or when there are too many zombies to handle.
- This and Lost City - Day 22 are the only Locked and Loaded levels with consecutive numbers in the game.