How to Sharpen Lawn Mower Blades for the Cleanest Cut, According to Turf Experts

A good mower will keep your lawn looking elegant and pristine, but an unsharpened blade can have adverse effects. Instead of neatly trimming the grass, a dull lawn mower blade will often tear it, putting undue stress on your lawn and making it more vulnerable to disease.

So what's the solution? Sharpening a lawn mower blade on your own may sound intimidating—or even dangerous—but it's a very straightforward, safe process if you follow the correct steps. Here, we spoke to the pros about how to sharpen your blade the right way, so your lawn will look more beautiful than ever.

Signs of a Dull Blade

There are several telltale signs that indicate your lawn mower blade needs sharpening. Thankfully, they're all pretty obvious, so you'll know exactly when it's time to have your mower serviced.

The first is uneven grass. Dull blades "tear grass rather than slice," says Mark Brokaw, go-to-market manager for turf parts at John Deere. So if you look behind where you've just mowed, you'll notice that the grass looks ragged and uneven.

Another sign is grass that turns brown, which can often happen as a result of uneven mowing. It's also important, Brokaw notes, to regularly check your lawn mower for nicks, dents, or scratches. This can help you catch damage early, before it hurts your lawn.

Don't Miss

Is Your Lawn Struggling? These 6 Signs Point to a Dull Mower Blade

How Often to Fertilize Your Lawn, According to Experts

Remove the Blade

Safety first! "We want to be as safe as possible," says Jeff Taylor, product service manager at STIHL. "So when we start dealing with the blade, we're going to put on a nice pair of work gloves." Next, follow these steps.

1. If it's a gasoline-powered lawn mower, make sure to disconnect the spark plug wire before you start working on it. This will prevent accidental starting: "It's possible if we started spinning the blade without disconnecting, the engine would start—and that would be extremely dangerous," adds Taylor.
2. Tip the lawn mower on its side so you can access the blade, ensuring that the air filter and carburetor are facing upward. Alternatively, Brokaw recommends using a lifting device to reach the blade.
3. You'll need a short piece of wood for this part. Taylor recommends a two-by-four or a four-by-four. Place the block between the blade and the mower deck, "so when I turn the blade counterclockwise, it’s going to stop the blade from turning," he adds.
4. Next, you'll need to remove the bolt that keeps the blade in place. You can use either a hand wrench or an air wrench, as per Brokaw.

How to Sharpen

There are a few different ways you can sharpen a lawn mower blade, depending on the tools you have on hand. But first, it's a good idea to clean it. "Use a wire brush, wire wheel, or battery-powered drill cleaning attachment," says Brokaw. "Clean the blade near the spindle and bolt hole, where fit matters most."

The first sharpening method uses a metal file. "You'll need access to a bench-mounted vise to hold the blade in order for you to sharpen it," says Taylor. Place the blade cutting edge up, usually at a 45-degree angle, then use the metal file to push across the blade until it has a clean edge.

For a "quick and efficient" sharpening, as per Brokaw, you can also use a bench-top grinder. Not everyone will have one of these on hand, but they are very popular with DIYers. Since this method involves a spinning grinding wheel, always make sure you put on a pair of safety glasses and work gloves first. Then, "position the blade, hold it at a 45-degree angle, and make passes over the grinding wheel," says Taylor.

How do you know when it's sharp enough? "The easiest way to describe it is a nice, clean edge," he adds. "It's not going to be razor sharp like a knife."

How to Reinstall

Before you reinstall your lawn mower blade, check to make sure that it's balanced. An unbalanced blade "can lead to vibration, which accelerates wear and tear on the mower's spindle," says Brokaw. "Over time, this can cause components to loosen or fail."

Brokaw recommends using a blade balancer or a pointed pyramid, but if you have a nail in a wall somewhere, you can also hang the blade on the center of the nail. "It should remain level—if one side dips, that side is heavier, and you can take a couple more strokes off," says Taylor.

When reinstalling, the most important thing to get right is the blade orientation. The blade has a cutting edge—the opposite side, the wing, should face towards the upper deck, and the cutting edge should face towards the ground.

"I turn it clockwise now," says Taylor. "I put my piece of wood to hold it in place, and I secure it." Brokaw recommends checking the blade clearance by quickly rotating the blade by hand.