Plants vs Zombies achievement - Lawn Mower Man

Hey guyz!
To get this achievement, there's 2 ways.
1. Wait until any zombie wave is near, then take down all your defences of a line that about 10 zombies are coming from.
2. Complete adventure mode, then do the first 4 levels again. On level 1-5,( wall-nut bowling) make sure 10 zombies are in the same lane, then stop bowling that lane down, and your lawn-mower will get them down.
Hope I helped!