Seriously, when was the last time you sharpened your lawn mower blade? Believe it or not, turfgrass experts say it’s best to sharpen the blade every 10 hours of mowing during the growing season. For most of us, that time is fast approaching, if it hasn’t already passed. But even if you’re a few hours behind schedule, your mower blade probably isn’t dull enough yet to cause serious harm. Just don’t get deep into August without giving it a fresh edge!
Why do lawn mower blades need sharpening?
A dull blade tears at the grass, creating jagged edges that not only look messy, but also make the lawn more susceptible to disease and drought. It’s bad for your mower too, since it forces the engine to work a lot harder. That in turn increases fuel use by up to 20%, according to the Cornell Cooperative Extension. If you’re on a battery-powered lawn mower, you’ll see a noticeable drop-off in runtime.
Your lawn will show signs of a dull blade, beyond the ragged cut. For example, it’s common for the tips of the lawn to turn brown, as the shredded grass blades lose water. And of course you can inspect the blade itself for signs of visible damage, including nicks, dents, and heavy rust along the cutting edge.
How to sharpen a lawn mower blade
There are some intrepid DIYers out there who sharpen their own blade, using a metal file or a bench grinder. But I tell most people to have their blades professionally sharpened at the hardware store or lawn mower repair shop. That said, it’s worth knowing how to take the blade off, since the shop will charge less if you bring in just the blade, as opposed to the whole mower—maybe $15 per blade, versus $30 if it’s still attached to the deck.
To safely remove the blade, start by powering down the mower, so there’s no way for it to suddenly spring to life. With a battery-powered mower, that means removing the battery. With a gas mower, you’ll need to take out the spark plug.
Before taking off the blade, put on heavy-duty work gloves, since even a dull blade can cut through the skin. Lodge a 2x4-inch block between the blade and the mower deck to keep it from spinning. Then use a wrench to loosen the fasteners that anchor the blade to the drive shaft.
It’s a good idea to take a picture of the blade and assembly so you’ll know the right way to put it back on after it’s been sharpened. It’s the same basic process as removing the blade, except you’ll insert the wooden block on the opposite side of the mower deck to keep the blade from spinning clockwise as you tighten the fasteners. If you’re not sure which way the blade should go back on, remember that the curved part should always be pointed up toward the mower deck.
One last tip: it’s a good idea to pick up a second blade for your lawn mower to use while the first one is in the shop.
Having written thousands of product reviews and how-to articles on all aspects of home ownership, from routine maintenance to major renovations, Dan (he/him) brings more than 20 years of industry experience to his role as the director of the Home Improvement & Outdoor Lab at the Good Housekeeping Institute. A one-time roofer and a serial remodeler, Dan can often be found keeping house at his restored Brooklyn brownstone, where he lives with his wife and kids.
