South of the borough the reservoir lies flat and gray on a January morning, mist standing above the water while the back roads glaze over. High Sierra Landscape Contractors Inc. reads that kind of morning early — plowing driveways, clearing paths to the door, salting the ice that forms where pavement stays cold all day. When the thaw finally comes the work turns green: mowing week to week, edging, trimming, mulch, hedge work, and the cleanups that bracket the year. Park Ridge sits high enough that weather here can differ from the valley floor by a few degrees, and a few degrees is the entire job. Knowing that difference is most of the craft.