Lawn Mower Cutting Unevenly

There’s nothing more frustrating than finishing a mow and seeing a striped, wavy mess instead of a smooth, even carpet of green. If your lawn mower cutting unevenly, you’re not alone. This is one of the most common problems homeowners face. The good news is that the cause is usually simple to find and fix yourself with a few basic tools and a little time.

An uneven cut, often called scalping or ridging, can make even a healthy lawn look untidy. It’s usually a sign that something is out of balance or needs adjustment. Let’s walk through the most likely culprits, from the simplest checks to the more involved fixes.

This main issue can stem from several areas. Before you worry about complex repairs, always start with these fundamental checks. They solve the problem more often than not.

Check Your Mowing Practices First

Sometimes, the mower isn’t the problem. Your technique might be contributing to that uneven look.

Mowing Too Low: Scalping happens when your mower deck is set too low for your lawn’s terrain. Bumps and dips in the ground will cause the blades to slice off too much grass.
Dull Blades: This is the #1 cause. A dull blade doesn’t cut cleanly; it tears the grass. Torn grass tips turn brown and can give a ragged, uneven appearance even if the height is consistent.
Mowing When Wet: Wet grass clumps together and can clog your mower deck. This leads to an uneven discharge and patchy cutting.
Speed: Going too fast, especially with a push mower, can cause the deck to bounce, resulting in an uneven cut height.

Inspecting and Balancing the Mower Blades

A bent or unbalanced blade is a prime suspect. A blade that’s even slightly warped will not cut evenly because one side is striking the grass at a different height or angle than the other.

Disconnect the Spark Plug: This is the most critical safety step. Always, always disconnect the spark plug wire before touching the blade.
Tip the Mower Safely: Tip it on its side with the air filter and carburetor facing up to prevent oil and fuel leaks.
Check for Damage: Look for obvious bends, nicks, or cracks in the blade. Even a small dent can throw off the balance.
Check the Balance: Use a blade balancer or simply hang the blade on a nail through its center hole. A balanced blade will sit level. If one side dips, it needs to be filed down (on the heavy side’s back edge, not the cutting edge) or replaced.

Examining the Mower Deck

The deck is the platform that houses the blade. If it’s damaged or clogged, your cut will suffer.

Clean It Out: Caked-on grass clippings (especially under the deck) disrupt airflow. This airflow is crucial for lifting the grass for a clean cut and discharging clippings evenly. A clogged deck leads to clumping and poor cutting performance.
Look for Damage: Check for cracks, rust holes, or dents in the deck itself. A significant dent can affect how air and grass flow.
Check Deck Level: This is a common fix. Your mower deck should be level from side to side and pitched slightly lower in the front than the back (for most models). Consult your manual for specifics.

How to Level Your Mower Deck

Place your mower on a flat, hard surface like a garage floor.
Measure the height from the floor to the edge of the deck on the left and right sides. Adjust the deck hanger linkages (usually a nut or bolt) until both sides are equal.
Then, measure from the floor to the front and back of the deck. The front should typically be 1/8 to 1/2 inch lower than the rear. This “pitch” helps ensure grass is cut once and lifted properly into the bag or chute.

Tire and Wheel Issues

Uneven tire pressure is a surprisingly common and easy-to-miss problem. If one tire is low, that whole side of the mower deck will sit closer to the ground, cutting that strip of grass shorter.

Check all tire pressures with a gauge, inflating them to the PSI listed on the tire sidewall or in your manual.
Also, check for worn or wobbly wheels. A wheel with a bad bearing can cause the mower to wobble as you push it, creating waves in your lawn.

Spindle and Pulley Problems (For Riding Mowers & Tractors)

If you have a riding mower with multiple blades, the spindles that hold the blades can wear out or become damaged.

A worn spindle bearing will allow the blade to wobble, creating an terrible uneven cut and often a loud noise.
Grab each blade (with the spark plug disconnected!) and try to wiggle it side-to-side. There should be very little to no play. If it wobbles, the spindle likely needs replacing.
Also, check that the drive belt that turns the blades is intact and properly tensioned. A loose or frayed belt can cause blades to spin inconsistently.

When to Seek Professional Help

Most fixes are DIY-friendly. However, if you’ve checked all of the above and the problem persists, it might be time for a pro.

A severely bent deck or cracked spindle housing may need specialized tools to repair.
If your riding mower’s transmission is causing one wheel to drag or slip, that’s a more serious mechanical issue.
Sometimes, a professional sharpening and tune-up is the best investment to get everything back in perfect sync.

FAQ: Fixing an Uneven Lawn Cut

Why does my lawn mower leave strips of uncut grass?
This is often due to a clogged deck, a dull blade, or mowing too fast. The mower can’t lift and cut the grass effectively before it lays back down. Check you deck clearance and blade sharpness first.

How often should I sharpen my mower blades?
A good rule is to sharpen them at least twice during the mowing season. If you hit rocks or sticks, check them immediately. Dull blades tear grass, making it more susceptible to disease.

Can a new lawn mower cut unevenly?
Yes. Sometimes the deck is not properly leveled from the factory, or the blades may have been nicked during setup. It’s worth checking the deck level on a new mower if the cut seems off.

What causes my mower to scalp the lawn in spots?
Scalping is usually caused by mowing too low for your lawn’s terrain, a wheel sinking into soft ground, or a deck that is out of level. Try raising your cutting height and leveling the deck.

Is it better to bag or mulch for an even cut?
For an even cut, both can work if your mower is well-maintained. However, mulching requires a very sharp blade and a clean, designed deck to chop clippings finely. Dull blades lead to clumping which smothers grass and looks uneven.

By following this checklist, you can systematically find and fix the reason behind your uneven lawn. Start with the simple stuff—tire pressure, blade sharpness, and deck cleaning. Most of the time, the solution is right there. With a little maintenance, you’ll be back to leaving smooth, clean stripes in your yard in no time.