This Achievement is pretty hard. It's unlocked by encountering the Zombie Yeti, which is found in level 4-10 after beating Adventure Mode for the first time. The Zombie Yeti will appear every time the player plays level 4-10, as well as in some random levels and some specific mini-games listed at their own page (it will only appear in minigames after you encounter it on level 4-10). You don't need to kill it to obtain the achievement. It will give diamonds when killed but will run away after a short time on the lawn so make sure you kill it.
Begin the level by picking Sunflower, Cabbage-pult, Kernel-pult, Potato Mine, and Wall-nut. Now, you should pack any instant-kill plants you prefer to use. Purchase the rake as well. This should be done on 2-1, and the guide is assuming it is. If you followed the procedure, getting this achievement will be simple.When the level starts, plant a Sunflower in the same row as the rake. Proceed to do so once more. At this point, do nothing but plant Sunflowers until you have at least five, keeping them out of harms way.Remember, don't plant them past the second row!