A reel gang mower has a plurality of front reel cutting units and at least trailing one rear reel cutting unit. Each rear reel cutting unit is centered on a gap between a pair of adjacent front cutting units to cover the gap. Each rear reel cutting unit has a cutting width that is wider than a common cutting width of the front reel cutting units by an amount which is sufficient to maintain positive overlap between the front and rear reel cutting units while mowing when turning or in sidehill mowing such that substantially no uncut strips of grass are left in a cut grass swath provided by the mower.