Try Expanding it a bit
The game is only really interesting for the first ...half a minute. You could definatley make this into a better game by using what you have here as "framework". Try adding some difficulty levels, and working on making the Special Effects (basically the animation that shows when you whack a plant) look better. Maybe add abilities that you can unlock with some sort of currency system, abilities such as slow down etc. that work toward's the player's advantage.