Behind the brownstones there is a second city of gardens — walled, quiet, reached down a hallway and out a back door. Linda's Lawn tends that hidden layer around New York, mowing the small squares of turf, edging the beds, trimming the shrubs and carrying the trimmings back out the way they came. These yards get maybe four hours of direct sun, so the grass is coaxed rather than driven, and the pace stays patient. In May the maples over the fence leaf out and the whole space goes green in a single week. Come autumn those same trees let go all at once, and the rakes come out again.