I gave my students a challenge last year to come up with non-violent shooting mechanics for games and they suggested a plant growing gun so I programmed up something during class. This is the result of that. Essentially you shoot a bullet at the ground or at another plant and it will grow some more plants where the bullet hit. You can customize how many more plants.
I had to put a limit on it because sometimes they would grow like DNA across the map. Since I also programmed the bullets to not get destroyed on impact they will sometimes get launched across the map when a new plant is added so the placement and randomization of the plant growth is pretty good, IMHO.
I ended up liking the results enough that I put the mechanic into my game as a grow gun. It acts as another way to build bridges and platforms for the player. The player can also use their regular destruction gun to destroy the plants if they want to.