Below the Franklin Falls dam the land runs wide and flat and river-made, with the Salisbury hills coming up green behind it in the middle of May. Tarbin Gardens works lawns in that country — the cut, the trim, the edge, and the cleanups that bracket a New Hampshire growing year at both ends. A mown lawn in this valley has a way of setting off everything near it: the beds, the stone, the shade the old trees throw by four in the afternoon. Grass gets cut on a schedule so that nothing gets away from anybody in July. The result should look effortless, which is exactly the part that takes the effort.