The High Line Canal threads southeast Denver with a long green ribbon, and the yards along its path borrow the same easy shade. R & R Landscape Management Co keeps them running all season, mowing, edging, trimming and handling the spring and fall cleanups, the ordinary upkeep that adds up to a good-looking block. Evening is the finest hour out that way, the light going amber, sprinklers ticking somewhere down the street, cut grass smelling like the whole month of June at once. A lawn is a slow project. It rewards showing up far more than it rewards ambition.