How often should mower blades be sharpened?

Sharpen mower blades about every four to six weeks during the mowing season. Sharpen sooner if you hit a stick, stone or curb, if the grass tips look frayed and tan after mowing, or if your lawn is tall fescue or zoysiagrass, which need it more often.

The schedule Virginia Extension gives

Virginia Cooperative Extension's lawn guide says to sharpen blades every four to six weeks during the mowing season, and that zoysiagrass and tall fescue turfs require more frequent sharpening than others.^[1] That is a guide, not a hard rule. Mowing frequency changes with the weather, and Virginia Cooperative Extension advises mowing often enough to remove only a third of the leaf height at once, which is probably every five to six days during the active growing season, and every 10 days or less when growth slows down.^[2]

Put together, four to six weeks is roughly every fifth to eighth mow in the growing season, and less often when growth slows in summer heat or late fall. Briggs and Stratton gives the reason in one line: Keep your mower blades sharpened so that you are cutting your lawn cleanly and not "tearing" the grass.^[3]

Why the schedule matters

A dull blade does not just look bad. Virginia Cooperative Extension says dull blades rip and tear the turfgrass, which promotes disease, causes the shredded leaves to appear tan and ragged, and results in weakened plants.^[2] Illinois Extension adds that a lawn cut with a dull blade takes more energy to recover and offers a longer opportunity for disease to infect exposed tissues.^[5]

Signs the blade is due early

You do not have to wait for the calendar. Sharpen or replace the blade when:

• the grass tips look frayed or tan a day after mowing (see why a lawn looks ragged after mowing);
• the mower struck a rock, root, curb or buried object, even if it kept running;
• you mow a rougher lawn with sticks, sandy soil or lots of acorns;
• the edge looks rounded or shiny when you tip the mower, or the blade has nicks you can see;
• the lawn is tall fescue or zoysiagrass, where the extension guide asks for more frequent sharpening.^[1]

A simple routine

A practical routine is to sharpen at the start of the mowing season and then repeat on the four-to-six-week mark, starting the count again each time. Mark the date on the deck or in a calendar so you can count.

Keep a spare blade. Swapping takes a few minutes, and you can send the dull one for sharpening. If you do it yourself, the method is in how to sharpen lawn mower blades. The cost of paying a shop is in how much mower blade sharpening costs in Virginia, and whether to do it yourself or have it done is a separate question.

Each time, make the mower safe first. Virginia Cooperative Extension's rule is "Disconnect the spark or electric plug before troubleshooting or repairing the mower."^[4] When the blade goes back on, Illinois Extension says to use a torque wrench to tighten the bolt to the specifications listed in your mower's user manual.^[5]

When a blade needs replacing, not sharpening

Sharpening removes metal, so a blade does not last forever. Replace it if it is bent, cracked, deeply nicked or worn thin near the tips, or if the sail (the upturned wing) is worn down. A replacement blade should match your mower's make and model.

Stop and call a pro if

• The blade is bent or cracked. Replace it. Do not straighten or weld it.
• The bolt will not come off or the head is rounded. A shop can free it without damaging the shaft.
• The mower shakes hard after a fresh blade. That points to a bent crankshaft or spindle.
• You do not want to handle the blade. A small engine shop can sharpen and balance it quickly.

Getting help in Virginia

Browse all lawn equipment repair answers or see lawn care services on Loclis. When you are ready, describe the mower and local small engine shops can quote it.