Yeah... I kind of knew that it was going to be an issue but at the time I didn't have any ideas excepted the reward for killing plants and to use the mowers which would force you to attack one row two times )because it would kill every zombies in a row), but the game doesn't have real-time zombie placement so you can't attack two different times in one row. Now that the jam is over, I realized there is actually an official game mode in pvz that is exactly like my game... but better. They solved the problem by changing the win condition to having to reach the end in all rows forcing you to attack in all of them.