Last Updated on February 16, 2021

What Causes a Riding Lawn Mower To Cut Uneven?

It’s been a part of the American dream for so many years, a beautiful lawn in front of your house and roses along the picket fence at the sidewalk.  It is a rite of spring to aerate, fertilize, treat weeds, and fill in bare spots with new seed and water.

Weekend lawn warriors cut, rake, and manicure, enjoying a glass of lemonade or a cold beer at the end of the day as they survey their domain.

It’s easy to understand, then, the panic and upset caused by the riding lawn mower cutting the grass unevenly. Whether the riding lawn mower cuts lower on one side, leaves a strip of grass, or scalps on a turn, it’s a frustrating day of yard work for a homeowner.

Troubleshooting A Riding Lawn Mower That Is Cutting Unevenly

Riding lawn mowers mulch grass clippings, collect them in a grass catcher or discharge them through a side shoot.  They are fun to ride, and the instant gratification we see from the seat as we turn and cut the next row is very satisfying.

For this work to be done, though, blades need to be sharp.  If the cut is uneven, the first place to look is the sharpness of the blades.  When was the last time the blades were sharpened?

Dull blades should be sharpened every year before the lawn cutting season begins, and if the blades don’t seem to be holding a sharp for you, they should be replaced.

If you’re sure the blades are sharp and don’t need replacement, check the mower deck’s level – that case below the seat in which the blades turn – may not be even.  Lawn mower decks can be adjusted to level, and the instructions that came with your mower will tell you how.

Another issue might be the motor.  A motor that runs slow will contribute to an uneven grass cut, too.  Perhaps a tune-up might be in order, or spark plug replacement.

Again, the instruction manual that came with the lawn mower will guide you through this process, and it’s probably a DIY task for you.

Inspecting the Blade Of Your Riding Lawn Mower

Checking your riding lawn mower’s blades has a bit of danger to it, so safety first is the rule.  It might sound unnecessary, but to be sure, pull the cover off the spark plug and tape it out of the way.  Grab a pair of leather gloves, too.

Turn the mower on its side with the air filter and carburetor (the part that mixes air with fuel for burning in the chamber) on the upside.  Remove all of the collected grass from the underside.

If the blade is visibly dull, or you see nicks and imperfections on the edge, it’s time for sharpening or replacement.  Local hardware stores and the larger DIY stores, as well as manufacturer dealerships, can supply replacement blades, and the instruction manual that came with your mower can guide you through installing new blades.

Servicing the Blade of Your Riding Lawn Mower

If you decide to service the blade of your riding lawn mower yourself, it’s a pretty easy task.  Use the same safety precautions as outlined above, and follow the mower manual’s instructions for the removal of the blade. You’ll need a wrench to loosen the blade bolt.

Place the blade in a vise to hold securely, and use a grinder against its cutting edge.  Make sure you use the same number of strokes with the grinder on both ends of the blade. 

Double-check the blade by suspending it by wire to determine its balance.  If it does not hang horizontally, grind it another few strokes on the heavy end, as a blade out of balance will not cut evenly.  If it was unbalanced while on the mower, that was the likely cause of uneven cuts.

Adjusting the Cutting Level of Your Riding Lawn Mower

The height of your riding lawn mower can be set by adjusting the height of each wheel.  Uneven height will contribute to an uneven cut, as you might expect.

The instruction manual will guide you through adjusting each wheel of the riding lawn mower, and a level (with the little air bubble inside a tube of water, you know what these are) will tell you when each is set to the right and even level.

Aligning a riding lawn mower wheel is an oft-found cure for uneven cutting and can fix the lawn scalping that is so maddening. They’re hard to hide, and you have to live with that ugly spot until it grows out. 

Final Thoughts on Riding Lawn Mower Performance

Yard debris, twigs, stones, and kid’s toys can cause blade degradation.  Check the lawnmower blades for this sort of damage, and determine whether a sharpening will be enough to cure.  If not, replace the blade and get a better cut.

Don’t try to cut too much in a single cutting.  Too much cut grass will accumulate and pack under the deck of the riding lawn mower, contributing to uneven/uncut patches.  This will be mostly on the right side of the deck/mower because of the blade’s turn direction.  Keep the setting to one inch of cut at a time, and you can avoid this.

An evenly cut, beautifully green lawn is a beautiful thing.  The smell of freshly cut grass can be intoxicating for the lawn enthusiast, and that cold beer on the patio as you look out over your yard at the end of a Saturday afternoon always seems to taste better than usual.

Take good care of your riding lawn mower, and all of that can be yours.


Author: Matt Hagens

Matt Hagens

Hi, I’m Matt the owner of Obsessed Lawn. I love to be outside working on my lawn, planning my next project. I created this website to help people like you find the best products for yard care and great advice. Learn more about me and find me on Facebook.