The player has to again deal with tons of zombies with the given plants. Though the tiny zombies are weaker, they are much bigger in numbers, and they are two times faster, making them a nuisance.
This means that Wall-nuts are slightly less effective in this level, though they are still crucial for passing this.
Try to aim for at least two Peashooters in each row and a column or two of Wall-nuts to defend the Peashooters. These zombies, although they take little effort to be killed, spawn in big groups to make this level difficult.