Sharpening your mower mulching blade is an important part of its maintenance. A dull mulching blade leaves jagged edges on plants that make them more vulnerable to disease. The frequency with which you should sharpen your mulching mower's blades largely depends on how much you use it and what it mulches. However, a good general rule is to sharpen your mower's mulching blade after every eight hours of use.
Disable the mower. If it is gasoline operated, pull out the spark plug. If it's electric, unplug it. And if it is battery-operated, disconnect the battery.
Turn the mulching mower on its side.
Immobilize the blade. Wedge the 2-by-4 between one side off the mulching blade and the bottom of the mulching mower.
Remove the mulching blade. Loosen the nut or bolt that affixes the blade to the mulching mower with a wrench.
Place the blade in a bench vice and secure it tightly.
Sharpen the mulching blade with a metal file. First, check the blade for any nicks, and file them away. Then, sharpen the blade. File the cutting edge of the blade from top to bottom using smooth, even strokes. Sharpen the blade until it is roughly as sharp as a butter knife, and count the number of strokes it took you to get there. Then open the vise, turn the blade around, and use the same amount of strokes to sharpen the other side of the blade.
Reattach the mulching blade to the bottom of the mower. Put on a pair of thick work gloves. Then hold the blade in place while you reattach the bolt. Tighten the bolt as tightly as you can, and assure that it is securely affixed before moving on.
Replace the spark plug or battery.