A mulching mower deck within which first and second mower blades rotate for cutting grass, having first and second blade chambers positioned adjacent each other and within which respective blades rotate during operation. The first and second blade chambers are generally completely enclosed for generally confining grass clippings within the blade chambers for preventing the clippings from exiting through side or top walls of the mower deck. The first and second blades travel in respective paths which overlap. The first blade is positioned to the right of the second blade with respect to forward operation of the mower deck and travels in a clockwise direction, and the second blade is positioned to the left of the first blade and travels in a counterclockwise direction. An opening is formed between the first and second blade chambers at a location where the blade paths overlap. Edges of the opening are positioned relatively close to the first and second blades near where the blade paths overlap. A flow divider defines the opening and is positioned generally above the location where the blade paths overlap, and extends downwardly from the top wall of the mower deck to a position in relatively close vertical proximity to the rotating blades where the blade paths overlap. The flow divider includes a portion directly in front of where the blade paths overlap, which acts to divide and direct air and clippings to respective blade chambers.