Took a bit to master the controls, but was quite a fun asteroid defense game! It ends up that the first bit is the most challenging while you frantically put down plant defense and then just fill in as they get taken away.
If you end up adding more, it might be fun to add some power-ups, and then stronger asteroids maybe for variety. Also some sound effects / music to amp it up.
Anyway, was a fun game! No bugs found on my end.