The land in Clarkstown tips east toward the Hudson, and from the streets above Central Nyack you can watch September come up the river in the morning haze. Klastow Landscaping LLC keeps lawns on that slope, where every mowing line has to be walked with a little more respect for gravity. Late-summer grass is tough and deep-rooted, and it takes a sharp blade to leave a clean cut instead of a torn one. Done properly, a hillside yard reads like a flight of shallow steps — level, deliberate, finished. Lawn care for Clarkstown, from the river slope out to the flats.