What To Do If Your Lawn Mower Is Cutting Your Grass Unevenly

If you've noticed your lawn mower cutting your grass unevenly, it doesn't necessarily mean it's time to replace your mower. It may just mean you need to sharpen your mower blades, or it could indicate one of several other issues ranging from simple to serious, such as a bent mower deck. Although there can be some instances where the fix requires a professional, most often it's possible to identify and correct the problem yourself by systematically troubleshooting.

The first step is to make sure the mower is level. It can become unlevel due to unequal tire pressure if the tires are inflatable, or from the height adjustment on push, self-propelled, and walk-behind models. To troubleshoot, find a clear, level area in your yard, driveway, or garage. Check the pressure in each tire, making sure they are all at the same — and recommended — level. Replace lawn mower tires that are damaged to ensure they continue to hold the appropriate air pressure. On push or self-propelled mowers, make sure all four wheel heights are the same. You should also make sure the adjustment levers aren't bent, causing one or more to sit at a different height.

Another potentially simple solution is cleaning under the mower deck and clearing any clogs from the discharge. When lumps of wet grass build up on portions of the deck, it can affect the lifting action required to cut grass evenly. This should be done regularly anyway to extend the life of your mower, so it's a bonus if it also solves your uneven mowing problem.

Given that mower blades are what cut the grass, it's not a surprise that they can be the part of the machine responsible for an uneven cut. This typically happens when they're dull, damaged, or unbalanced. Again, sharpening your mower blade should be part of your routine maintenance, so if it's been a while since you sharpened it, this could be the problem. Additionally, even a fresh blade can become bent or damaged by hitting a solid object. Start by disconnecting the power source, then inspect the blade. Bent blades or those with large gouges or dings should be replaced.

While inspecting the blade, you should also make sure it is adequately sharp. You can do this by pulling a piece of paper across the cutting edge. If it's sharp, it should cut through the paper without much pressure. If it is dull, remove and sharpen it. Although there are several different ways to sharpen mower blades, the key to each is to avoid oversharpening the blade. Blades that are excessively sharpened become too thin and are more easily dulled.

After sharpening, it's important to check the balance of your mower blade. An unbalanced blade will wobble on the spindle while it rotates. This can result in an uneven cut, as well as damage the mower. To that end, it's a good idea to check the balance even if you did not need to sharpen it in order to rule that out as a possible cause of the uneven cutting. This is easily done by placing the blade atop a blade balancer and checking that it sits level. 

Aside from the need to clean and unclog your mower deck, other issues with it could also be the problem. One of the other culprits is a bent or unlevel mower deck. Just because all of your tires are inflated to the same pressure and the mower itself is level doesn't necessarily mean the mowing deck is as well. When inspecting the deck, if you notice it is bent or severely damaged, it will need to be repaired or replaced to remedy the issue. Unfortunately, you may need professional help with repairs unless you choose to replace the deck yourself.

Should the mower deck appear undamaged, use a tape measure to make sure the height is consistent around the entire deck. You can also use a level to ensure the deck is even, both forward and back and side-to-side. Correct any variance by amending the height adjustments, deck linkages, and brackets. If you are unsure how to make these adjustments, consult your owner's manual for instructions.

Finally, check for wear or damage to other components of the mowing deck, such as belts, spindles, linkages, and pulleys. Any worn, frayed, or cracked belts should be replaced. Check the spindles to make sure they are straight and not loose and wobbly. This can be done with a level as well as attempting to move the spindle back and forth by hand. Be sure to remove the power source first. Replace mower deck spindles that are damaged, loose, or bent; otherwise, they will continue to produce an uneven cut.