By June the harbor at Great Kills is a thicket of masts, and the breeze that comes up off it carries straight into the yards behind Hylan Boulevard. Grass grows fast in that damp salt air — a week away and the lawn has ideas of its own. Greenscape Landscaping SI keeps ahead of it with regular mowing, clean edges along the walks, trimming where the mower can't reach, and the cleanups that bracket the season at either end. Cut on a Thursday, a South Shore lawn will hold its stripes right through a weekend of company on the deck. That's the point of the work, and it's a good one.