The North River runs slow and brown at thaw, and the ground along it in Marshfield gives up winter reluctantly, an inch at a time. Curran Corp Landscape & Excavation reads that ground for a living — where the water goes, where grass will take, which lawn wants cutting and which wants leaving alone a week longer. Through the season that means mowing, edging, trimming and the heavy spring and fall cleanups nobody enjoys and everybody notices. Through the winter it means plowing drives and opening walks while the marsh grass lies flat under white. Standing at the end of a finished job with the river light coming through is most of the reason to do it.