A yard that has been looked after gives something back every day — somewhere to sit when the work is done, a path that carries you to the door without your having to think about it. Summit Landscape Construction builds those places in Nashua, setting patios, retaining walls, and walkways in a city whose working vocabulary has always been granite and brick, where the Nashua River bends toward the Merrimack past the old mill blocks. The work starts underground, with excavation and drainage — the unglamorous grade that decides whether an April rain leaves or lingers — and rises into plantings, outdoor lighting, pergolas and gazebos, fire features, outdoor kitchens, and inground pools. Come the dark end of the year, the same ground asks for a different kind of attention: snow and ice management on commercial properties across the Hillsborough County hills, lots opened up while the streetlights are still the brightest thing out. What lasts is the line of a wall holding a slope patient and square, and the long blue hour when the lamps come on along a walk that was bare dirt in spring.