Your lawnmower blade does more than just cut grass—it impacts the overall health and appearance of your lawn. A sharp blade slices through grass cleanly, while a dull blade tears it, leaving jagged edges that can turn brown and invite pests or diseases. Knowing how often to sharpen your mower blade depends on factors like how often you mow, the size of your lawn, and the type of grass you have. Keeping your blades sharp and in good condition isn’t a difficult part of routine maintenance, and it can make all the difference for your yard.

Signs Your Lawn Mower Blade Needs Sharpening

There’s no one-size-fits-all answer to how often you should sharpen your blade, but paying attention to your lawn and mower will give you clues. If you notice these signs, it’s time to break out the blade sharpening skills:

• Torn or shredded grass rather than neatly cut grass clippings.
• You see browning or frayed grass blades after mowing.
• Your lawnmower seems to strain more than usual while cutting.
• The blade looks visibly dull or nicked when inspected.

On average, most homeowners sharpen their mower blade after every 20-25 hours of mowing. For a small yard that’s mowed weekly, this might mean sharpening once or twice a mowing season. Larger yards or lawns with tough, thick grass may require more frequent sharpening.

Factors That Affect How Often You Need to Sharpen

How often you need to sharpen your blade depends on several factors:

• Frequency of mowing: The more often you mow, the faster you end up with dull mower blades.
• Type of grass: Thick or coarse grass can dull blades more quickly than fine grass varieties.
• Lawn debris: Rocks, sticks, and other debris in your yard can cause damaged blades and dull, blunt mower blades.
• Blade quality: Higher-quality blades stay sharp longer than cheaper alternatives.

If you’re mowing frequently or dealing with challenging conditions, it’s a good idea to inspect your blade more often.

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How to Sharpen Your Average Lawnmower Blade

Sharpening a mower blade isn’t difficult, but safety comes first. Always wear gloves and eye protection and disconnect the spark plug wire to prevent accidental starts before getting near the mower deck. Here’s a quick step-by-step guide:

1. Remove the blade: Use a wrench to loosen the blade bolt. Some mowers have reverse-threaded blade bolts so don't rely on "lefty-loosey, righty-tighty". If you can't hold the blade and turn the bolt you may need to wedge a 2x4 in the mower deck for extra leverage to help hold the blade still.
2. Inspect for damage: Check for cracks or excessive wear on the cutting edge. If it has extensive damage it's time for blade replacement.
3. Sharpen the blade: Use a flat file, angle grinder, bench grinder, or dedicated sharpening tool to restore a clean, sharp edge. We don't know an exact angle of sharpening, just make sure you keep a consistent angle. It also doesn't need to be razor sharp. A razor sharp edge can become dull faster and is more prone to damage.
4. Balance the blade: After sharpening blade, make sure the blade is balanced. An unbalanced blade will create vibrations during mowing. It's not super scientific, but I put a screwdriver in the center hole (bolt hole) and do a crude balancing.
5. Reattach the blade: Tighten it securely, with the correct side facing up.
6. Clean up the mower deck: While you're in/under there you may as well clean out the clumps of grass or mud or anything else that can contribute to dull lawn mower blades.

FAQ

What happens if I mow with a dull blade?

Dull mower blades tear grass rather than cutting it cleanly, leaving the edges ragged and prone to browning. This not only makes your lawn look less healthy but also stresses the grass, making it more vulnerable to pests and diseases.

Can I sharpen my mower blade too often?

Yes, over-sharpening is a common mistake and can wear down the blade unnecessarily and shorten its lifespan. Stick to a consistent sharpening when the blade shows signs of dullness or after 20-25 hours of use to avoid excessive wear.

What do I do with my old blades?

If you're like me you keep your original blades as a backup. I always have extra sets of blades "just in case". I can also swap in the spare blades and keep mowing between sharpening. If you're not like me, you could donate them to Habitat for Humanity or similar charity, take them to a recycling center, take them in and get cash at a scrap yard. Check your local rules to see if you're allowed to dispose of them with your normal trash pickup.