A maintenance route is really a kind of calendar. For Garden City Landscape Maintenance Co., Inc. it opens with April clearing, runs through mowing, edging and trimming all summer, and then lengthens into the leaf work that starts when Webster Woods turns and lets go over the yards along Beacon Street. After that the sheet becomes a storm list: driveways and lots plowed, walks and stairs cleared, entries salted before anyone leaves the house. Properties tended by the week rather than rescued by the emergency simply hold their shape better. Newton is a city of closely kept yards, and that steadiness shows from the sidewalk.