Last summer my lawn mower began to leave streaks and uneven cuts of grass in my yard. This got me thinking about why my mower was cutting grass unevenly and how to fix my lawn mower so that it cuts level.
It’s extremely frustrating to spend time in the summer heat mowing your lawn only to notice that the finished product is an eyesore of unevenness, uncut grass. Rather than buy a brand new lawn mower, there are some things you should check first. Some of the most common reasons why lawn mowers cut uneven are a bent or dull blade, underpowered mower, bent mower deck, uneven wheel adjustments, and mowing too quickly. With these tips, you’ll be able to diagnose and fix your lawn mower so that it cuts evenly and makes your lawn look great this summer.
Signs that Your Lawn Mower is Cutting Uneven
Below is a list of the top reasons why lawnmowers cut unevenly and what problems can arise from prolonged use. Most symptoms of uneven cuts are immediately obvious and should be addressed quickly to prevent damage to your lawn.
Top Warning Signs that Your Mower is Cutting Unevenly
- Lawn Mower is Leaving Uncut Grass or Strips
- One Side is Cutting Higher than the Other
- Lawn Mower Leaves Streaks
- Grass is Not Being Cut Completely
- Mower Leaves Swirl Marks in the Lawn
Lawn Mower is Leaving Uncut Grass or Strips
Lawn mowers that fail to cut the full strip of grass are the leading cause of what most consider uneven cutting. The uncut strip of grass is usually 2-4 inches wide on the outside edge of the mower swath.
Uncut strips of grass require multiple pass through attempts and increase the time it takes to mow your yard considerably.
One Side is Cutting Higher than the other
This symptom is often detected when one side of the blade digs or cuts into the lawn resulting in blade marks on the grass that can look white in appearance. This low cut on one side exposes the lower stem of the grass stalk which is sign that a lawn mower is cutting unevenly.
Exposing of the lower grass stem can result in your yard becoming susceptible to disease, drought, or freezes.
Lawn Mower Leaves Streaks
Lawnmower streaking can be any combination of uncut crass, wheel marks, or uneven cuts. These symptoms leave long uniform line or “streaks” in the grass for the entire pass through.
Streaks caused by lawnmowers can create dead patches of grass or bare areas that promote weeds and undesirable plants to take hold.
Grass is Not Being Cut Completely
Another sign that your mower is not cutting evenly can be that the grass just isn’t being cut efficiently. This can result in one side of the cut being higher than the other, strips of grass not being cut, and bent or torn grass blades.
Bent or torn blades of grass resulting from uneven cuts can help introduce common lawn diseases such as Brown Patches.
Mower Leaves Swirl Marks in the Lawn
Uneven cuts are an eyesore and can even leave swirl marks from the blade on your lawn. Not only does this reduce mowing efficiency; it puts a tremendous strain on your lawn mower itself.
Swirl marks are a good indicator that grass is not being cut completely and your grass is likely being torn or bent.
What Causes a Riding Lawn Mower to Cut Uneven?
Now that we’ve discussed the common telltale signs that your mower is cutting unevenly, let’s take a look at the top causes of why mowers develop these issues and how you can diagnose them.
Top Causes Why Riding Lawn Mowers Cut Uneven
- Bent Mower Deck
- Bent Blade
- Dull or Loose Blade
- Underpowered Mower
- Uneven Wheel Heights
- Mowing Too Quickly
- Mowing With the Grain
Bent Mower Deck
The most common reason lawn mowers cut unevenly is that the mower deck is bent. Improper storage, stepping on the deck, or storing items on top of the mower while not in use can cause uneven cuts.
To make sure you mower deck is not bent; examine it at eye level for any noticeable bends or defects. Check if all wheels are touching the ground. If not, you likely have a bent mower deck that needs to be addressed.
Bent Blade
Lawnmower blades come in contact with tree stumps, rocks, and other immovable hard objects on a regular basis. The force of a spinning mower blade coming in contact with a hard object can result in the blade giving way and bending.
Bent blades can create a wobble that results in uneven cuts and even scraping or grubbing the ground surface.
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Dull or Loose Blade
Lawnmower blades wear down over time and the effectiveness of the blade is diminished with use. Dull blades can result in uneven cutting, tearing grass, or no cuts at all.
Loose blades can be a symptom of a bent blade, but they can be exacerbated by improper installation. Lose blade nuts can lead to blades that wobble and create uneven cuts.
Underpowered Mower
One of the most overlooked reasons why mowers cut uneven is that they are simply underpowered. Low horse power mowers can bog down in tall grass. This causes incomplete and underpowered blade cuts that result in streaking, uncut strips, and uneven cuts.
When it comes to lawnmowers, more horsepower is always better. Always try to stay above 5HP when looking for a new mower since it will handle most tall grass with ease.
Uneven Wheel Heights
Lawn mowers that cut unevenly can often be the result of uneven wheel heights. Most lawn mowers have height adjustments on each wheel that allows you to raise and lower the mowing deck.
These heights should always be the same across all 4 wheels to help insure an even cut. Wheel height settings can be jarred out of alignment with regular use so they should be checked routinely.
Mowing Too Quickly
Let’s face it, it’s hot out and there are probably other things you would rather be doing than mowing your yard. Rushing to get done is the one of the top causes why mowers cut unevenly.
Mowing too quickly can cause your mower to hop when it hits bumps, bog down as it gets overloaded with grass, and not make complete and uneven cuts. Rushing to finish quickly can lead to an eyesore of a lawn.
Mowing With the Grain
This cause is often overlooked when discussing lawn mowers cutting unevenly, but it’s extremely important. The grain is basically the direction that you’re mowing. If you mow with the grain, such as starting on the outside edges and working your way to the center, you will have mowed completely with the grain.
Why does this matter? Because mowing with the grain can cause uncut strips of grass to develop in the previous passes that were laid down by the mowers wheels. This strip of grass is not vertical during the next pass and does not get cut effectively.
Always cut against the grain, i.e. cut the opposite direction of your last pass, to insure grass isn’t being laid over by your wheels and not reaching the cutting surface.
How to Fix a Lawn Mower that is Cutting Uneven
So far we’ve talked about how to diagnose you lawn mower that’s cutting uneven and why mowers cut unevenly, but now let’s talk about how you should go about fixing your lawnmower so that these issues a remedied. As always, make sure the lawnmower is not running and the spark plug wire is unplugged prior to any work being conducted.
Top Fixes for Lawn Mowers that are Cutting Uneven
- Level the Mowing Deck
- Replace or Sharpen Lawn Mower Blade
- Mow More Frequently
- Adjust Wheel Heights
- Mow Slower
- Adjust Mowing Style
1) Level the Mowing Deck
First, diagnose if your mowing deck is bent or simply not adjusted properly. If your mower deck is bent, use a level to determine the proper degree of adjustment. Slowly bend or shape the deck back to its original location while using the unbent side as a guide.
Check to make sure each wheel is firmly touching the ground. The mower deck may still need to be adjusted if only three wheels are touching the ground.
2) Replace or Sharpen Lawn Mower Blade
Lawnmower blades should be sharpened or replaced yearly. Inspect your lawnmower blade prior to each use for nicks in the blade or lose blade mounts.
Nicks or gouges in the blade can cause uneven cuts and loose mounts can cause the blade to wobble. Sharpen and tighten the blade as needed.
3) Mow More Frequently
Lawnmowers work harder in tall grass, so mowing more frequently helps not only to prolong the life of your mower, but produce a more completely cut lawn.
Mowers that bog down in tall grass can require multiple passes and may not even cut the grass completely. Mowing more frequently (every week) can help reduce the time to takes to mow your yard and reduce the chance of uneven cuts.
4) Adjust Wheel Heights
Almost every lawn mower comes with wheels that are capable of being adjusted for height. Height adjustments are usually in 1 inch increments and range from 3-6 inches in overall travel.
To make sure your lawnmower is cutting evenly, routinely check all wheel heights and adjust accordingly. As the temperature rises, the highest setting is always the best.
5) Mow Slower
The easiest tip to incorporate for mowing your yard evenly is to just mow slower. We all get in rushes and mowing in the summer heat is no different.
Slowing down how you go about mowing your yard can make a huge improvement in the overall result. A 25% reduction in speed can be the difference in 5-10 extra blade revolutions over a given spot that could increase the evenness of your lawn.
6) Adjust Mowing Style
The last tip for mowing your lawn evenly is to adjust your mowing routine in order to systematically tackle the job as efficiently as possible. Developing a mowing pattern that goes against the grain helps reduce the chance of uncut strips of grass showing up on the outside of your mowing lanes.
Additionally, mowing less grass per pass can help reduce streaking or other signs that your mower can’t handle what you’re throwing at it. Try cutting your pass down to 3/4 or 1/2 of a swath, rather than a full pass.
Bottom Line
Push lawn mowers cutting uneven is a common occurrence if you’ve dealt with mowers for any extended period of time. Many mowers develop these issues after prolonged use, but the symptoms are always the same.
Push lawnmowers that cut uneven are diagnosed by leaving strips of uncut grass, streaks, torn or bent grass, or swirl marks. These symptoms of uneven cut grass can often lead to a disastrous looking lawn and in the worst case lawn disease.
Issues contributing to uneven lawns are usually caused by bent mower decks, underpowered mowers, bent or dull blades, loose blades, and mowing too quickly. The good news is that these issues can be fixed quickly and easily in most cases.
Bent mower decks can be leveled out and bent back. Mower blades can be sharpened and tightened prior to use. Slowing down your mowing speed can help the blade make more passes over the same spot and provide a more even cut. And purchasing a mower with enough horsepower for the job will help increase efficiency across the board.
If your lawnmower is cutting uneven strips of grass, diagnose the issue to help find the problem. It’s usually something very simple that can be fixed in a matter of minutes!
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