September takes the crowds off Mount Desert and leaves behind the light — long, low and gold across the lawns above Asticou. Songscape Gardens works in it, mowing and trimming and cutting a clean line where turf runs up against the beds. Grass this time of year grows slow and dense, and a lawn given a few last good cuts will hold its color deep into November. The reward is the moment the mower shuts off and the yard has nothing left out of place. Then the leaves arrive all at once, the cleanups begin, and the whole green season is carried away inside a week.