Mulching mower
Also called: mulching blade, mulch plug, 3-in-1 mower
A mower whose deck and blade are designed to chop clippings finely and drop them back into the lawn instead of discharging or bagging them. Mulched clippings return nitrogen to the soil and don't cause thatch.
Most modern walk-behind mowers are “3-in-1”: they can mulch, side-discharge, or bag, switched by inserting a mulch plug or plate that closes the discharge chute. In mulch mode the clippings circulate under the deck and get cut several times before falling between the grass blades, where they decompose within days.
Mulching supplies roughly a quarter of a lawn’s annual nitrogen needs for free. The persistent belief that clippings cause thatch is wrong — thatch is made of stems and roots, not leaf blades. Bag only when the grass is very long and clumping, wet, or diseased.
It works best with a sharp blade and the one-third rule: if you’re cutting off six inches at once, no mower mulches it cleanly.