20 Below Zero (PvZ2)

For other uses, see 20 Below Zero.

Difficulty: Easy

20 Below Zero is an achievement in Plants vs. Zombies 2: It's About Time. It requires you to freeze 20 zombies with one Iceberg Lettuce with Plant Food. It is worth five points.

Strategies
The easiest way to obtain this achievement is to use Ancient Egypt Day 24. Day 24 is behind the Sun Boost upgrade. Working in columns from left to right, fill as much of the board as you can with Tall-nuts. Allow the level to play out, but be ready to act quickly. Do not panic when the Explorer Zombies start burning the Tall-nuts! Moments before the Explorer Zombies reach the lawnmowers, a large amount of zombies will come onto the screen via whirlwinds. Once they have appeared on the board, very quickly place the Iceberg Lettuce and freeze every zombie with the Plant Food.

Another way to earn this achievement is to wait until the final wave of a 3 or 4 flag level and then use the Plant Food on the Iceberg Lettuce once they are all on screen. Check your achievement page to make sure you got it and repeat as necessary.

Trivia

 * This is the only achievement in Plants vs. Zombies 2: It's About Time that its first word starts with a number.
 * This and SPUDOW! are the only achievements available on both games.