Why Does My Lawn Mower Leave Lines?

Summertime is finally here! Judging by the size and scale in which grass grows throughout the season, you’re probably going to be mowing the lawn a bit more often.

Typically, a self-propelled lawn mower leaves behind an even and level surface, but if there are any internal problems with the machine, you may start to notice lines on your lawn. The lawn maintenance term for this is “streaking” and refers to when rows or clumps of grass do not get cut properly even when you’re using the appliance correctly.

In this post, we will discuss why this happens and what you can do to fix it.

Why Does My Riding Lawn Mower Leave a Strip of Grass?

There are a number of reasons why your lawn mower leaves lines. The problem can be with the way that you mow or with your lawnmower. 


Pay attention to mistakes due to overlapping as you operate your lawn mower. The correct way to trim a lawn is to cut in rows as if you were making a grass trail. Unless each row overlaps with the adjacent row, you’ll start to notice your lawn mower leaving streaks that are long and thin.

Those are the areas between rows that the blade hasn’t cut over.

The overlap doesn’t have to be huge; between 1 and 2 inches should be enough. 

Blade Size

If you’ve just replaced your blade and still notice streaks of missed grass across your grass trail, it might be because you’ve purchased the wrong size.

To avoid this, refer to the manual provided by your manufacturer before you purchase new blades. It contains all the information you’ll need with regard to the configuration of your lawn mower, including the blade size so that you can get the correct blade.

Mower Blade Damage

One of the main reasons that a lawn mower leaves clumps of grass is due to a defective or improperly positioned cutting blade. 

If you start noticing uncut grass while mowing, the first thing you should do is troubleshoot the blades to see if they are nicked, curled, or blunted. If the problem is dull blades, you can simply remove and sharpen them. However, if the blades have sustained any damage or are bent, your only recourse would be to replace them.

This is because, in addition to making your lawn look uneven, a dull blade can be detrimental to grass health. It leads to discoloration, which leaves the tips of your grass an unhealthy yellow. Dull blades can also cause water loss, lawn diseases, and dead grass.

Engine Speed

Your mower can also leave streaks if the engine performance is insufficient. Grass is different everywhere you go. Some grass can be more robust and require high-speed blades for a clean, fresh cut.

This is an easy problem to deal with. Simply adjust the throttle on your mower as directed in your instruction manual to make the engine speed faster. In short, if it’s not working, try more power.

Clogged Deck

Clogged Lawn Mower

If you’re using your mower regularly, the underside will collect dirt, grass clippings, and maybe even some small pebbles. This debris can slow down the drive function of your mower by restricting the movement of the components inside your deck.

The result is reduced speed and streaks on your lawn. The only way to get the debris out is with a thorough cleaning. Be very careful while disassembling the mower for cleaning; you don’t want to cut your hands on the blades.

Improper Mowing Technique

If you’re using a self-propelled lawnmower, remember to let the mower do the work, which might take time. However, if you try to rush it by moving too fast, it will result in uneven mowing.

The correct way to mow is to walk slowly in straight lines with a firm grip on the mower. The drive function from the engine will push the lawnmower slightly ahead as it is cutting the grass. Follow the speed of your mower, not yours.

Low-Quality Equipment

Like any piece of machinery, lawn mowers deteriorate with time and may need parts changed, such as the tires, blades, wheels, belts, etc. Make sure you purchase these components from a reputable vendor or directly from the manufacturer if they make them so you can be sure to get the right parts.

Why Does My Mower Leave Clumps Of Grass?

Tall Grass

It’s perfectly fine to leave grass clippings on the lawn because 25% of it becomes fertilizer for the soil. On the other hand, clumps of grass are quite unsightly and prevent the grass underneath from receiving sunlight, so it’s best to use a rake to get them out.

These clumps can form for a variety of reasons, such as:

Wet Grass

Water makes grass clippings stick together and form lumps. There’s not much you can do to control the weather, but if it’s raining, save mowing for another day, so it’s less work.

Tall Grass

Grass and hair share some similarities. When you let it grow for too long and then try to cut it, you end up with lumps. It’s important to maintain an interval of no more than one week between mowing to avoid this.

Push Mower Blades

Grass clumping is more common with push lawn mowers which don’t chop grass into fine pieces as a driving mower would. Finer clippings are less likely to form clumps. 

Final Notes

Indeed, having a lawn entails a lot of maintenance. However, a perfectly even, lustrous, and healthy lawn is a thing of beauty.

In this article, we’ve shared with you some of the most common reasons for lawn mower leaving streaks and what you can do to solve them. For good measure, we recommend that you also refer to your lawn mower’s user manual before making any changes.