A mulching lawnmower eliminates the need to rake, bag or otherwise dispose of grass clippings, but it doesn't simply make the clippings vanish into thin air. The design of a mulching mower's blade and mowing deck differentiate the machine from a conventional lawnmower and give it the ability to turn cut grass into nearly invisible mulch.
Grass Clipping Dispersal
A regular lawnmower, one not equipped for mulching duty, is often called a "two-in-one mower" because it can deal with grass clippings in two ways, either discharging them through a side chute or directing them into a bag mounted on the mower. Many mulching mowers receive the designation "three-in-one" because they can handle grass clippings in the two ways a regular mower can plus another way -- chopping grass clippings into pieces so small that the clippings don't need to be discharged from under the mower deck .
Recirculation vs. High Lift
In order to do its mulching magic, a mulching mower needs to cut grass clippings more than once. In order to accomplish that task, it is equipped with a blade designed with curves and bends that create a recirculating air flow that moves the clippings across the blade repeatedly. In contrast, a standard lawnmower's blade, sometimes called a high-lift blade, is designed only to throw clippings forcefully upward and outward so they're quickly and easily discharged from under the mower deck.
Blade Cutting Portions
A standard mower blade usually has cutting surfaces only at its ends while a mulching mower's blade usually has multiple cutting surfaces along its length. With its numerous sharp edges, a mulching blade is able to chop grass clippings as they fly in the air flow under the mower deck.
The design of a mulching mower's deck also helps it keep grass clippings circulating around the blade. Some mulching mower decks are higher and more deeply domed than standard mower decks, giving clippings more room to move in the air flow under the mulching mower decks. Also, some mulching mower decks are equipped with baffles that channel and direct clippings and air for optimal air-stream circulation under the decks. On some models, the baffles are adjustable, allowing the mulching mowers to be switched between mulching and discharge modes.
Because the design innovations that give a mulching mower the ability to reduce grass clippings to a tiny size are focused on keeping the clippings under the deck as long as possible, a mulching mower isn't as good as a standard mower at moving clippings from under its deck. So a mulching mower is likely to perform less well than a conventional mower for side-discharge and bagging of clippings.
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