Last Mown Standing is an achievement that can be obtained on iOS and Android versions of Plants vs. Zombies. It is worth five points on Game Center. It requires the player to defeat the last zombie in a level using a Lawn Mower.
This achievement's name comes from a portmanteau of the phrase "last man standing," used in children's outdoor games and "mown," or the past tense of mow.
Time to start Adventure Mode. Just start a level like you normally do and when it says "Final Wave," remove all the plants on one row and the Lawn Mower will kill those zombies and you will get this achievement. You may also be able to earn Lawn Mower Man and possibly also Close Shave. However, in order to get the Close Shave achievement, you must empty all the rows.
You can earn this when playing Level 1-1 for the first time. To do this, try to limit yourself to two Peashooters, and place them around the second column from the right side of the lawn, so that the zombies will be able to eat them easily during the final wave. However, be aware that sometimes one zombie will survive and it may eat your brains.
Note: This can easily be achieved, but remember, when you see the last zombie, do not defeat it or you will not get the achievement.