A shift mechanism for trim mower cutting units includes a pair of slidable carriers. Each slidable carrier can slide along a pair of guide rods mounted to a mower frame. A hydraulic extension cylinder is connected to each slidable carrier and independently extends to move the slidable carrier laterally outward from the mower frame or retracts to move the slidable carrier laterally inward in relation to the mower frame. A hydraulic shifting cylinder is mounted between the two extension cylinders and extends to shift both slidable carriers laterally inward toward a center position, and retracts to move both slidable carriers laterally outward toward an extended position.