Why Do Your Lawn Mower Blades Dull So Fast?

A lawn mower is only as effective as its blades. Blades that need sharpening give warning signs that indicate their condition — think clumpy cuts and uneven grass, even after hours of mowing. While there are telltale signs that it's time to replace your lawn mower blades, there's also a good chance that the blades are simply dull. In fact, lawn mower blades can lose their edge faster than expected, even when they've been sharpened to a T. It may seem counterintuitive, but razor-sharp edges are actually more prone to chipping and wear. For this reason, it's better to sharpen the blades to an edge that resembles that of a butter knife rather than a razor.

Lawn mower blades don't just cut grass; they also come into contact with whatever solid materials are in the grass. Rocks, pine cones, sticks, sand, and even molehills nick the blades and wear down their edges. Even soil can cause abrasive friction and take the sharp edge off the blades, especially if you push your mower over uneven ground. Wet grass can cause problems, too, since it can form clumps around the mower deck, forcing the blades to work harder than necessary. Then, there's the fact that the blades simply wear down over time. Once the blades are no longer in pristine shape, the mower's performance can suffer, and manicuring the lawn becomes more labor-intensive.

Everyone can make mistakes when sharpening lawn mower blades, especially first-time owners still learning the dos and don'ts of lawn equipment maintenance. One common mistake is over-sharpening. Each sharpening session removes a layer of steel, so doing it too often will gradually thin the blade. A thin blade is more likely to bend, break, or even shatter when it strikes hard objects hidden in the grass. Over-sharpening can also cause the blades to dull faster, which can take a toll on the engine by forcing it to exert more effort to get the job done. Therefore, knowing when to sharpen the blades is just as important as knowing how to sharpen them.

As a rule of thumb, lawn mower blades should be sharpened after roughly 20 to 25 hours of mowing. If you're not one to keep track of usage time, however, just sharpen them twice per season. Got fast-growing turfgrass or a lumpy, rocky lawn? You can take a more instinctive approach to blade sharpening. The moment the mower hits a stick, rock, or other piece of solid debris, stop the engine, turn the machine over, and inspect the blades for dents or cracks. Sharpen them on the spot if necessary. You may be able to go longer between sharpening sessions if you only use your mower occasionally on a smooth, obstacle-free lawn. Otherwise, simply sharpen the blades as soon as you notice they're not cutting the grass as cleanly as they were before.