Brooklyn has a spine, the old glacial ridge that runs through Green-Wood and lifts Sunset Park toward the harbor, and a garden on a slope asks more of you. Groundworks Inc. handles that ground with mowing, edging, evening out the tired spots, mulching the beds, cutting back and hauling away at the close of the year. October turns the hillside copper and the leaf work begins in earnest, week after week, until the branches stand bare. Underneath all of it is soil that has been worked and reworked since this end of the borough was farmland. Coaxing it to hold grass again is the satisfying part.