Installing a lawnmower blade incorrectly can leave your yard looking rough and your mower struggling to cut. If you’ve just sharpened or replaced your lawnmower blade and suddenly your grass blades look torn rather than neatly trimmed, there’s a chance you might have the blade on upside down. It’s a surprisingly common mistake, especially for those new to mower maintenance. The good news is that this blade issue is easy to diagnose and a manageable DIY fix.

How to Tell If Your Blade Is Installed Upside Down

Incorrect blade installation ruins cutting efficiency because the sharp edge isn’t positioned to do the work. Instead, the dull trailing edge of the blunt blade hits the grass, lowering blade speed, and leading to a jagged, uneven cut. 

Not sure what to look for? Here are some signs:

  • The grass blade looks ripped or shredded instead of neatly cut.
  • You see large clumps of grass after mowing instead of clean clippings.
  • Your lawnmower vibrates excessively when mowing.
  • The blade doesn’t spin smoothly or seems to struggle with resistance.

To confirm, turn off the mower and safely tip it on its side (with the air filter facing up). Look at the mowing blade—most have a stamp or engraving that says “This Side Up” or “Grass Side.” If this marking is facing the wrong direction, the blade is upside down.

Sharpening a lawn mower blade by hand.
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Steps for Properly Installing Standard Lawn Mower Blades

Fixing an upside-down blade is simple, but safety comes first. Wear gloves to protect your hands from the sharp blades, and before working on the mower, disconnect the spark plug to prevent accidental starts. Once you’ve done that, follow these steps:

  1. Remove the blade: Use a socket wrench to loosen the bolt holding the blade in place. Some mowers have reverse-threaded bolts for their mower blades so "lefty-loosey, righty-tighty" may not be the case for you. Take note of how the original blade is currently positioned and the direction the cutting edge is facing. If you can't hold the blade and turn the bolt you may need to wedge a 2x4 in the mower deck to help hold the blade still.
  2. Inspect the blade: Look for any markings, such as “Grass Side” or “Bottom.” The side with these markings should face the grass when reinstalled. While inspecting the blade check for blade damage like blade cracks.
  3. Check the edges: The sharp, beveled edge of the blade should be positioned downward to cut the grass, while the flat edge should face upward.
  4. Reinstall the blade: Align it correctly, then tighten the bolt securely to hold it in place.

Once the blade is reinstalled, reconnect the spark plug and test the mower to make sure it’s working correctly.

A Husqvarna riding lawn mower doing final cleanup in the fall.
After making the swap, reconnect the spark plug and take it for a spin. Credit: Emily Fazio

How to Avoid This Common Mistake In The Future

Installing a mower blade upside down is an easy mistake to avoid if you follow a few basic practices:

  • Know the direction of rotation: If you know the direction your blade spins, you can easily tell if the cutting edge is facing the right way. Most likely the blade will spin toward the discharge chute.
  • Always check the markings: Most standard cutting blades are labeled to indicate which side should face up or down.
  • Refer to the manual: Your lawnmower’s user manual will have clear instructions for replacement blades, installation and correct blade orientation.
  • Use gloves: Wearing gloves helps you handle the blade safely and get a better grip when positioning it.
  • Keep a routine: Regularly inspect and clean your blade to make future maintenance more straightforward.

Person mows the lawn with a push mower.
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FAQ

What happens if I mow with an upside-down blade?

Using a mower with an upside-down blade results in a rough, uneven cut that can damage your grass and lowers the efficiency of lawnmowers. The shredded edges make your lawn more vulnerable to diseases and pests, and the mower’s performance will suffer due to increased strain on the engine and blade.

How often should I sharpen my mower blade?

A mower blade should typically be sharpened after every 20-25 hours of use. Dull blades can make your grass look as bad as an upside-down blade, so regular maintenance is important to keep your lawn looking its best.