April in the Hauppauge flats south of Smithtown arrives as a smell before a color — thawed soil, cut grass, the first mow of the year. Diamond Exterior opens the season there with cleanups: winter sand off the walks, broken limbs out of the beds, the lawn cut low once to wake it up. From then until November the work is weekly and rhythmic, mowing and trimming and keeping every edge honest against pavement. Exteriors are what people see first, and a well-kept lawn does more for a frontage than almost anything else on it. The route runs through Smithtown, Hauppauge and the neighborhoods between.