How to Sharpen Lawn Mower Blades: 3 Easy (and Safe!) Ways

Save yourself time and money while making lawn care a priority this summer, and get in the habit of sharpening your lawn mower blade yourself.

Why a Sharp Lawnmower Blade is Important

A sharp blade cuts faster and causes less damage to the grass in your yard. It’ll create clean cuts, whereas a dull blade can fray the ends of the grass and pull at the roots of your lawn. Manufacturers recommend sharpening the blade after every 10 hours of use, but you may need to do it more often if you’re running over debris like branches and pine cones.

Step 1: Remove the Blade From the Mower

Disconnect the spark plug or remove the battery to prevent an unintentional start. My lawn mower folds to store compact and upright, which makes access to the blade easy. If you’re tipping your lawn mower to reach the bolt, it’s a good idea to check your user manual to make sure you don’t accidentally saturate the air filter with oil or flood fuel into the engine. Either can happen if you tip the lawn mower the wrong way — always keep the spark plug tilted toward the sky.

Block the blade with a piece of 2x4 or place a piece of 3-inch pipe through the side discharge and over the blade to hold it in place. Use a wrench to loosen the bolt that holds your lawn mower’s blade in position.

Note: Put the lawn mower up on blocks so you can access the underside without having to tip it.

Step 2: Sharpen the Blade

When you’re sharpening your lawn mower blade, the goal is to make the blade as sharp as a butter knife. It doesn’t need to be razor-blade sharp to be effective since it rotates at a high speed.

There are three common ways to sharpen a lawnmower blade.

Method 1: Clamp and File

A flat file is an easy tool that'll sharpen a dull blade. Secure the blade secured in a vice. Apply pressure to the file, and run it perpendicular to the edge of the blade to grind down imperfections in the metal and hone the shape of the existing edge. Once you’ve done one side, reposition the blade in the vice to do the other side. The process is slower than using a hand file, but it works.

Method 2: Use a Bench Grinder

The fastest way to sharpen a lawnmower blade is with a bench grinder. Wearing protective eyewear, earplugs and work gloves, grind the edge of the blade against the spinning wheel. It'll be loud and you'll see sparks, but you’ll be able to sharpen the blade in a few minutes. A bench grinder is also great for repairing a heavily damaged blade that’s riddled with gouges that are hard to file smooth by hand.

Method 3: Use a Drill and Blade Sharpening Stone

A blade sharpening drill bit operates much like a bench grinder but on a smaller (and more affordable) scale. It’s faster than hand filing, and the stone of the bit is designed to hug the edge of your lawn mower blade, making it easy to sharpen with little effort and room for error.

Once both sides are sharp, check the balance of the blade by hanging it on a nail through the bolt hole. If it hangs horizontally, it’s ready to re-install. If one end hangs lower than the other, file a bit more off that end’s edge until the blade balances on the nail. This will ensure that the mower runs smoothly.

Step 3: Reinstall the Blade

The only critical part to remember when you’re installing your lawn mower blade is to get it tight. After you’ve reassembled and threaded the bolt by hand, use a wrench to tighten it down. Use a 2x4 or pipe to stabilize the blade as you tighten the bolt. Remember to reconnect the spark plug wire. Start it up over the lawn, and enjoy how easy lawn care can be when you have a freshly sharpened blade.

Lawnmower Blade Sharpening FAQs

How do you know if your blade needs to be sharpened?

Here are some signs that you should sharpen your mower blade:

• The mower leaves a rough, ragged finish.
• The blades of grass look torn rather than cut.
• A day or so after mowing, the grass has brown tips.
• It’s been at least a year since it was sharpened.

How often should you sharpen your mower blade?

If the mower is used regularly, plan on sharpening at least once a year. A yearly sharpening should go hand-in-hand with an oil, filter and spark plug change.

If your mower is used heavily or there are a lot of weeds, sticks or other debris in the grass, up to several times per summer may be necessary. If multiple sharpenings per season are required, consider buying a second blade (or set of blades) to have on hand for a quick change out that can save time on mowing day and allow sharpening to be done when it’s most convenient.

Mower blades should last a very long time, possibly the life of the mower. However, an unsafe or worn out blade should be discarded and replaced with a new blade matching manufacturer specifications for your mower. Discard a blade when it is bent, cracked, worn thin on the back edge (opposite the cutting edge), deeply rusted or otherwise structurally compromised.