The type of mower doesn’t matter, but the blade’s condition does. A dull blade tears at the grass. Take a close look at a grass blade a few days after mowing. If the blade is dull you’ll notice a jagged brown line across the tip of the cut grass. This is a good indication that your blade needs sharpening. Professional mowers sharpen their blades about every 8 hours of use. For most homeowners, once a month is recommended. The jagged edges caused by a dull mower blade make it more difficult for the grass to fight off pests and disease.