How to Sharpen Your Lawn Mower Blades – And Why

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Springtime is in full force; flowers are in full bloom, trees are leafing out, and I’ve had my 50th allergy headache. It’s a beautiful time to be outside. It is also time to start really cutting your grass. If you’ve had a spring like I have, you’ve already cut it a couple of times, but it really hasn’t started to grow in that well yet. But now that there’s more sunlight and warmer weather  (and if you’ve aerated the lawn to promote good growth!), the grass is sure to grow like gangbusters, and you need to make sure that your equipment is ready to handle this onslaught. So if you haven’t yet, you definitely need to sharpen your lawn mower blades.

Eh – Why Bother to Sharpen the Lawn Mower Blades

Let’s be honest – you wouldn’t shave with a dull razor and you wouldn’t cut tomatoes with a dull knife. Why then would you try to cut grass with the same lawn mower blade, untouched and unsharpened, that came out of the box in 1984? You’re better off taking a whiffle ball bat to the grass.

There are four important reasons why you need to sharpen your blades every year.

  1. Looks – One of my favorite philosophers – Anon – said, “It’s better to look good than be good.” And while this has been my mantra career-wise, (It’s better to sound like you know what you’re talking about than to actually know it, abbreviated by many as B.S.) with your lawn mower blades this is only half true. Having sharp lawn mower blades means your grass does look better, but it’s also actually better all around. See, dull lawn mower blades tear and fray grass blades instead of neatly cutting them. The result – your grass looks like an old grunge rocker after leaving a mosh pit instead of a neatly trimmed Antonio Banderas.
  2. Health – Cleanly cut grass with a sharpened lawn mower blade is less susceptible to diseases like fusarium blight, necrotic ring spot, Justin Bieber Fever, and gout…  OK, just the first two. The tears increase open surface area and access to the vascular system of the grass, allowing more areas for bacteria, fungi and the like to get into. It’s similar having your arms ripped off, as opposed to a simple cut on your arm – there’s just more chance that you’ll have some nasty infection creep in (in addition to a few other experiential differences, in the case of the arm thing).
  3. Growth – Research (I know – grass research?!) has shown that grass cut with a sharp blade actually grows faster than grass that’s been cut with a dull lawn mower blade. While you may be wondering if this is in fact a good thing, lawn health and lawn aesthetics all get better with growth rates.
  4. Money – A sharp lawn mower blade can save you up to 22% in fuel costs. I know, it’s like a 1/16th of a gallon per cut, but that can add up, especially as fuel prices continue to grow (much as your grass will as when you sharpen your lawn mower blades).

Now – How to Sharpen Lawn Mower Blades

There are a variety of different tools that you can use to sharpen your lawn mower blades; files, angle grinders, bench grinders, and even a Dremel attachment and rotary blade. The choice is up to you, but the method never changes.

  1. Safety-Shmafety – A lot of professionals will at least mention that if you truly want to be safe, you should remove the spark plug wire or the spark plug itself. You know – in case you, while trying to remove the blade,  start the motor like one of those old prop airplanes. Take the precaution you feel you need to, but I will suggest at least wearing eye and perhaps ear protection for grinding, and wearing work gloves throughout the process.
  2. Removal – Remove the blade from the mower. You can use a 2 x 4 block, wedging it between the deck and the blade to keep the blade from moving while you crank on it, or just hold on really tightly and crank. By the way, when I mention “hold on tight” in this article, I don’t mean grabbing the sharp part of the blade with your bare hand, OK?
  3. Vise it Up – If you’re using a hand held tool, put the blade in a vise to keep it steady – otherwise hold on loosely but don’t let go… OK scratch that.  You should probably hold on to the blade tightly.
  4. De-nicking – Perpendicularly grind or file the leading edge of the blade to remove any nicks or gouges that may have occurred when you ran over sticks, stones, or the 9/16” wrench that your son was “playing” with when you were at work.
  5. Hone it –  Now it’s time to get that edge. Grind or file the blade at the factory-made angle (assuming that you didn’t grind that into oblivion in step 4). Check the grinding occasionally to make sure you’re not over grinding it or rounding it off, and continue until you’ve got a nice sharp blade.
  6. Balance– Presumably you’ve sharpened both ends of the blade, but during the sharpening you may have removed more on one side than the other. To check, either put the blade on a lawn mower blade balancing cone or anything else that you can find to balance it on, and see if the blade will balance in the center. If it won’t, remove extra metal from the blunt backside of the heavier blade to balance everything.  Uneven blade rotation can cause bad things.  Just think of a short-sided helicopter prop – that could rip your arm off!
mowing the lawn
Happy cutting!
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About Leroy

LeRoy was born into a long line of contractors/carpenters/missing links which maybe why he fell naturally into tools and fishing with his paws, errr, bare hands. He has since punctured, stabbed or electrocuted every appendage that can be discussed in mixed company. Given his natural fur vest, he has never been cold. In his parallel life he is a mild mannered environmental scientist where he builds, destroys and builds again. Which let’s face it is much cooler than Superman’s parallel life.

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4 thoughts on “How to Sharpen Your Lawn Mower Blades – And Why”

  1. Assen must be talking about an old fashioned push reel mower;
    that’s all I’l use, you can’t hear the blades cutting grass with those dang noisy smelly fossil fuel burn in contraptions.

    I’ve heard that valve grinding compound is a good way to sharpen a reel mower; has anyone tried that? Any tips?

    • If I had a relatively small, relatively level space, I’d love to use a reel mower. Makes one get out more often and get some exercise keeping the length manageable.

      Check this out:

      Actually, I did mean the stinky, loud gas-powered mower. Especially with a sharp blade, one can throttle it down a bit to reduce the noise and actually hear a difference of it slicing through the grass.

  2. … also, the sound of a freshly sharpened blade cutting grass is really nice (the small things in life one enjoys).


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