10 Signs of Dull Mower Blades You Shouldn’t Ignore

6. The Blade Is Dented or Bent

Visual damage like dents or bends is a clear sign of dull mower blades—or worse. Blades can get damaged over time. If there are any sizable dents or if the blade is bent, it needs to be sharpened or completely replaced.

Damage	Action
Small dents or nicks	Can often be sharpened out
Bent blade	Replace immediately (balance will be off)
Cracks or missing chunks	Replace—safety risk

7. Frequent Stalling

While multiple factors can cause stalling, dull mower blades that force the engine to overwork are a common culprit. Sharpening your blades may resolve the issue—and it is part of knowing how to maintain mower blades.

Symptom	Likely Cause
Engine stalls during use	Dull blade strains the engine
Mower shuts off in thick grass	Blade cannot cut efficiently

8. Discolored Lawn

A dull blade can leave yellow or brown streaks, a classic case of damaged grass from dull blades. Grass that is shredded instead of cleanly sliced loses moisture and becomes disease-prone.

Color Change	Why It Happens
Yellow or brown streaks	Torn grass loses moisture and turns pale
Uneven green color	Damaged grass recovers slower

9. Blade Pulls Up Chunks of Grass or Dirt

Rather than cleanly slicing through grass, a dull blade can not only pull clumps of grass from your lawn but some dirt as well. The blade should always slice the grass, not pull it.

Sign	Meaning
Clumps of grass left behind	Blade is yanking grass, not cutting it
Dirt and roots disturbed	Extreme dullness—action required immediately

10. It’s Been a While

Lawn mower blades should be sharpened every 20 to 25 hours of use time, according to The Home Depot. If you would rather not sharpen the blade, they are not overly expensive to replace.

Time Since Last Sharpening	Recommendation
Less than 20 hours	Likely fine (but inspect regularly)
20–25 hours	Time to sharpen
25+ hours	Long overdue—sharpen or replace

What to Do About Dull Blades

Noticing the signs of dull mower blades is only the first step—knowing how to fix the issue keeps your lawn healthy and your mower running smoothly.

DIY Blade Sharpening Methods

Sharpening your mower blade at home is a simple DIY activity that can make the blade last longer and work better as you mow.

Step	Action
1	Unplug the spark plug to keep the engine from starting by accident
2	Use a wrench to remove the blade—remember which side is down
3	Put the blade in a vise or clamp to hold it steady
4	Use a flat file, bench grinder, or blade sharpening equipment to sharpen the edge
5	Always keep the edge at the same angle
6	Use a blade balancer to check balance (uneven blades cause vibration)
7	Reinstall the blade, making sure it is tight