I added the check for the boundary back for the projectiles, destroying them if they cross it. I duplicated this functionality for the growths as well. I also remove the excess object from the physics engine, so it seems that things are being properly destroyed now.
I adjusted the collision detection for the growths to only cause a destruction if they bump something other than another growth. This needs to be updated further to properly use the health functionality instead of immediately destroying the growths. Also, the projectiles need to get similar collision detection, since they are not being destroyed until they reach the edge of the screen.
With too many growths on the screen at once, the game bogs down and crashes. I'll need to address this. Possibly, it will be taken care of when I add the death sequence for the player.