Half the stone walls in Durham run through woods now, and the apple trees they once fenced still bloom every April in the corners of yards. Yankee Yardworks tends the ground around all of it — mowing, trimming, edging and seasonal cleanups while things are growing, and plowing, shoveling and sanding once they are not. Old New England yards are full of obstacles with a past: a granite step, a well cap, a wall that wanders where it likes. Mowing them cleanly is a puzzle worth solving, and so is working out where a plow can go without touching any of it. From one season to the next, the aim holds steady — a place that looks looked-after.