Why Does My Lawn Mower Leave Lines?

Believe it or not, the first time when I asked myself the question why does my lawn mower leave lines, I discovered that the ‘upside down’ installed blades were the reason.

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That stupid mistake cost me many stressful hours and unplanned costs. Unfortunately, this is not the only reason for this issue. Let’s check together possible causes and solutions to avoid that tiny errors lead to annoying problems.

Reasons Why Does Your Mower Leave Lines

In general, lawn mowers are very reliable units. Tune-up them, change the oil approximately every fifty hours, sharp the blades regularly (at the start of the season if possible), and clean their air filter after every 25 hours, and you can expect your machine work without serious problems.

Common lawn mowing problemsThe way of manifesting
StreakingThin lines of uncut grass on your lawn
Stepped cuttingSharp ridges on your lawn
Uneven cuttingWavy troughs on your lawn
StingersUncut patches of grass on the lawn
ScalpingThe deck of the mower strikes the ground


There are a few primary reasons why does your reel mower leave rows of grass between two blades. The most common one is blade damage, which means that you should check them first if you are facing such a situation. In a case that they are sharp and undamaged, you can consider other possible causes. Let’s see.

1. Blades damage or their wrong position

Blades damage or their wrong position

When you spot a problem with cutting, you should check if your blades are defective, nicked, warped, or curled. If it is so, you can expect them to lead to uneven cutting, unpleasant vibrations, and consequently to poor grass collection. Their replacing is the only solution for this issue.

Also, it is not rare that your blades are placed upside down or unbalanced. If you changed them recently, just check their orientation and whether they are well attached. If it is a problem, you can solve it for a couple of minutes by placing them in the right position.

2. Blunt blades

If you use a self-propelled lawn mower without sharpening the blades, you may notice left uncut lines on your lawn. However, those lines are not the only problem here. Blunt blades can also severely and quickly damage grass in your yard. As a result, you will spot jagged yellow tips on the cut grass.

Simply said, if you want a beautiful yard with healthy and lush grass, you need to cut it regularly by using sharp blades. To be sure that they are sharp and prepared for mowing, do sharpening at least once a season, depending on the type of the terrain and how often you need to cut your lawn.

3. Blades size

If you have been using your mower for years without any problems but noticed rows of missed grass after you had replaced blades, the possible cause could be their inadequate size.

You need to double check if the new blades are too small or short for the model of the mower you have. If it is a case, they can’t fully cover the cutting area, and you will get uncut lines behind. The only solution is to replace the blades with those of an appropriate size.

4. Overlap mistakes

Pay attention to overlapping the rows while operating the mower. If you don’t overlap them enough, the blades will pull grass upward. At the same time, the mower’s tires will push the grass down and prevent pulling up a thin line of it.

Consequently, you can’t reach the grass under the tires and cut it if you overlap rows just into the tire tracks of the row you previously mowed. The solution is to place the current tire path inside the previous ones and to overlap mowing rows by a few inches.

5. Engine performance

Engine performance

Sometimes you can face problems with engine performance, including incorrectly set throttle. It is not a big deal to set it to fast/run while cutting and you don’t need an expert to do it. You can finish those settings by yourself.

The additional issue can be connected with adjustment of the throttle cable. You can expect that your mower won’t cut as usual when the engine power is reduced. It is especially noticeable when you hit a patch of heavy grass in some parts of your yard.

6. Old fuel

Can you believe that you often can’t use the fuel you bought the previous season? Yes, if the oil you pour into the engine is too old, you will probably have problems with lousy engine performance. Actually, if you use fuel older than four to five weeks, it may go stale and gum up the inside of the mower’s carburetor.

That way, the fuel feed ports will become blocked, and the engine may work slow and sluggish. The result will be a poorly cut lawn and the occurrence of uncut lines. You can quickly solve the issue by draining the fuel tank and adding fresh oil.

7. An inadequate speed of mowing

If you try to mow your lawn too fast, you will get uncut lines as a result. The solution is simple. Just take your time, don’t let the engine operates at full throttle, and try to work slower.

8. Errors you are responsible for

If you want to have a perfect lawn, you need to eliminate errors which depend on you. The most common ones are:

  • You purchase low-quality equipment
  • If you try to run the mower at low engine speed, the blades can’t spin quickly enough, and they will leave strips on your lawn
  • Bad tire pressure or unevenly inflated tires can be common causes of lines left on the lawn
  • If your lawnmower doesn’t have a floating deck and you turn it over too quickly and too sharp while mowing, the result will be missed grass all over your yard


Have you ever asked your self – Why does my lawn mower leave lines? It is a common question many lawnmowers’ owners ask themselves. I have given you the most common causes of the possible problems which you can quickly solve.

Read the user manual before using the mown for the first time, maintenance your mower regularly, and use it appropriately. That way, you will always enjoy the beautiful lawn. You deserve it.

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