A "mulch plug" is necessary to mulch the grass clippings during mowing. The plug is used to close the discharge opening in the mowing deck and recycle the lawn clippings back into the blade area for repeated cutting and eventually deposited into the lawn as fine mulch.

Are mulching plugs any good?

A conventional mower with a mulch plug fitted (available for most mowers) is not usually a good mulch mower. At Eco Garden Maintenance we have tried fitting mulch plugs to some very expensive professional lawn mowers and the results have been ok but no way near as good as a properly designed mulch mower.

Can you use regular blades with mulch plug?

I put a mulch plug on with regular blades, worked good that way.