The Importance of a Sharp Lawnmower Blade

David T writes…

“… in interviews with several of my fellow landscapers I’ve come to realize that they really don’t understand the concept if a truly sharp lawnmower blade…”

It kind of goes without saying that blades should be sharp.

Scissors, box knife, steak knife…a dull blade results in a painfully ragged cut. And that is never a good look.

Not buying it? Go on in the kitchen and pull out that box of aluminum foil. See that jagged little cutter edge? Good. Now go shave with it.

But, in all fairness; keeping your lawnmower blade sharpened and balanced is easy to overlook.

That whole “out of sight-out of mind” thing can be a booger.

Luckily your grass doesn’t scream in agony when you spin a dull blade across it, but if it did that would make remembering much easier.

So you’ll just have to make a special effort to think about it from time to time. I find checklists are a good thing.


Any way you “slice” it, cutting grass damages grass. We all know that grass is pretty capable of taking care of itself.

Since dirt became fertile, grass has been bouncing back from everything from dinosaurs to DDT.

But, that’s what nature is all about. Heck! A little sunlight, a little air and a little water and them leafy little fellers will be sprouting again in no time!

When living things get broken (like when a lawn mower blade blasts through it), they have to heal and as we already discussed, grass will do that quite nicely on its own. But using a dull blade will only delay the whole “bouncing back” process. And over time, it can have a very lasting effect on the health of your lawn. And by “lasting effect”, I mean kill.

What I’m getting at here is that a sharp blade is better than a dull blade. 

To put it in perspective; there is a valid reason why heart surgeons prefer the scalpel over the chainsaw when making incisions.

A chainsaw would make a mess. It’s bad enough with all the maniacal laughter and the co-ed’s running for their lives and the screaming and stuff. But the patient is now losing copious amounts of fluids at a record rate, the wound has left the patient vulnerable to disease and infection. Not to mention filing all those insurance forms. Thanks Obamaaaa! Then there’s the loooong recovery time and all the oogie-ness, which is pretty much a medical term for when stuff gets all gunky and drippy and- look! Let’s just agree to agree here that clean cuts heal easier, in less time and with less scarring.


The same stuff happens to your lawn. Ragged cutting causes rapid moisture loss which is going to draw out the time it takes for your grass to heal and continue growing. Moisture-less grass is a bad thing. Using a dull blade in an arid region? Fuggedaboutit!!

Ragged cutting leaves you with an ugly lawn. That’s right, I said it. U-G-L-Y! You ain’t got no alibi! Yep.

Loss of moisture causes a browning in the ends of the blades, which often results in lawn issues being misdiagnosed. Many a home owner has dumped ridiculous amounts of water and fertilizer on an otherwise fine lawn when they should have checked the blade first.

Ragged cutting leaves the grass vulnerable to infection and disease. Sometimes that brown, splotchy stuff isn’t dry grass, it’s sick grass.

Finally, a dull blade can cause undue resistance when cutting, specifically through longer growth. And that additional resistance on the blade is going to start to reveal all those little worn out parts on your mower.


The life of the blade will be determined by how often you cut, how much damaging debris you’re banging around the yard, and the type of soil.

Cutting too often hinders the grasses ability to heal. You’ve got to give it a break every once in a while. Sure, heavy rains cause heavy growth, but even the old testament kids knew to let the land rest.

Running over foreign objects is a bad, bad thing.

Take my advice and pick up your yard before mowing. Or…I suppose you could make a game out of it.

Like, “guess what you hit by the sound alone”. Lego’s make a quick, crunch/ping sound. Stuffed animals are more of a warbling, ripping / choking / “fffrrrap” sound.

And a baseball? That would be a resounding “I wonder how late the mower shop is open today?” bang.

As far as determining when to replace the blade can be as simple as inspecting it.

Never turn the blade by hand without disengaging the spark plug first. How does the engine start up? We turn the crankshaft, which is attached to the blade!

Nicks, notches…not great but livable. Dullness needs to be fixed and for those of you with a bench grinder and a lot of gumption, just remember that you don’t need a razors edge on your blade. In fact, it has been argued that the narrower the edge, the
faster it degrades.

This has never been truer than when cutting in sandy soil.

I have said it before and I’ll say it again…sand is the great equalizer. Sand does not care what blade you put on your mower. It will eat it up and grind it down to nothing. Sure, there are a few manufacturers out there producing “sand” blades. I can’t speak personally to the effectiveness of these hybrids, but if the Great Sphinx has anything to say about the effect of sand; I think it might sound something like “Sand wins! I quit!”

It’s just my personal opinion but when you’re cutting in sandy soil…buy cheap, buy often. Why pony up $40 for a high tensile snack for your sandy soil?



Now this is an extreme but very common example of a worn out blade. Consider the following question when examining the picture…”Where did all that metal go?”

Answer: It went flying off the blade like tiny little ninja stars.

So, before a piece of your blade ends up whacking the neighbors cat from 60 feet away, make sure to inspect it regularly.

  • Look for rounding on the outer corner of the cutting edge. Given that the outer inch to 1 1/2 is the part of the blade doing most of the cutting, you’ll notice the greatest wear here. Keep in mind that metal can’t be replaced, so once the blade starts rounding off, sharpening is not going to help.
  • Look for thinning of the blade at the back side of the cutting edge. If erosion turned a creek into the Grand Canyon, your blade doesn’t stand a chance. And once it starts to thin out, that’s pretty much it. The image above reflects the blade of a person who either didn’t realize they get dull, didn’t care they get dull or didn’t want to pony up the cash for a new one.
  • Look for nicks, pits or notches. A lot of these can be ground out, but they can also result in hidden cracks and fissures in the steel.
  • Bent blades? Broken blades? Get rid of them.

When in doubt, have a technician inspect the blade for you. You may not want to have to buy a new one, but you really can’t afford not to.


I’d say that “cuts” right to the chase.



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Bill Brown

Bill is the head of content creation for the LawnMowerPros Blog and DIY section. He’s been in the Outdoor Power Equipment Industry for years and he’s still learning new things everyday. You can often find him creating featured articles, DIY guides, videos, graphics and much more.