Why Does Grass Turn Yellow After Cutting?

Let’s explore why this might be happening so you have an idea of how to keep your lawn healthy, lush, and green. 

There are multiple reasons why lush green grass can turn yellow after cutting, most of which have to do with how you are maintaining and caring for your yard:

• Lawn mower has blunt blades
• Grass is being mowed too short
• Extreme weather
• Exposed thatch

If you are reading this, you are seeking lawn care answers, and we’ve explored the many reasons why your lawn might be turning yellow after mowing. Keep reading to discover what we’ve found out about this common lawn-care question. 

What Causes Your Lawn to Turn Yellow After Mowing? 

It can be disappointing to mow your lush green lawn, and when you finish and survey your handiwork, your lawn looks yellow.

What is going on that is causing your green grass to turn yellow? 

The most common reasons your lawn turns yellow after mowing are:

• Blunt blades on your lawn mower
• Mowing the grass too short
• Environmental Extremes
• Exposed thatch

Now that we’ve pinpointed why your green grass turns yellow, let’s look at each of the items in this list and learn how they affect your grass. 

Your Lawn Mower 

The most obvious reason to consider grass turning yellow after you’ve mowed it is your lawnmower.

It’s possible your lawnmower blade is blunt and needs to be sharpened, or you need to adjust the lawnmower’s height. 

Let’s look at each of these issues separately:

The lawnmower blade

If just the top part of the grass is turning yellow after you’ve mowed, most likely the blade needs replacing. A dull blade won’t cut the grass; it will tear and damage it so that the edge dries out and turns yellow. There is an easy solution here—either sharpen the blade or replace it.

The height of the lawnmower blade

If you cut your grass too short, you are exposing the sheath. The sheath is tannish yellow; the green part, also called the leaf blade, pushes out from the sheath. It stands to reason that if you cut too much of the leaf blade off, you expose the sheath, and your grass will appear yellow. There is an easy solution for this problem as well—adjust the height of the lawnmower to cut less off. 

Both these problems are easily solved, but the question now is, how much of your lawn should you be trimming off? 

The general rule of thumb is never to trim more than one-third of the total grass height.

Figure out how long you want your lawn to be and do the math. If you miss mowing your lawn a few times, and it’s too long, resist the urge to get it back under control by cutting it too short; you’ll have exposed the sheath and a yellow-looking lawn.

Environmental Extremes 

A lush green lawn needs plenty of sunshine to keep it looking healthy; however, too much sun can cause issues that become evident after mowing. 

Sunscald will cause your lawn to look dried out and off-color; dry soil can cause the same result.

Prolonged periods of heat are brutal on grass and will weaken and damage the blades and dry out the soil.

When you cut the top portion of the grass off, you expose grass blades that may wilt and yellow due to stress.

Too much sun isn’t an issue you have control over; however, you can water your lawn to help it through extreme heat. Read these tips for watering your lawn to keep it looking healthy and green. 

Exposed Thatch

And then there’s thatch—what is thatch, and how does it affect your lawn? 

Thatch is naturally occurring and is the build-up of dead plant material around all grass plants’ sheath and upper roots.

Thatch is important; it protects the root system and can help deliver nutrients back into the roots. However, too much thatch: 

• Promotes moisture retention that can contribute to disease and pests
• Can inhibit nutrients from getting to the root system
• Limits the amount of oxygen that can get into the soil

Mowing also contributes to thatch. Thatch can build up to the point where when you mow, it looks unsightly—it can present as tan-yellow or brown and makes your yard look unkempt, especially after cutting.

The solution to removing unsightly thatch is simple; just dethatch:

1. First, determine if you have a layer of thatch; grab a sample or plug of your lawn, and if there is half an inch of decaying grass between the upper growth area and the soil, it’s time to dethatch.
2. Grab a thatching rake and bring the layer of dead grass up to the surface, being careful not to damage the roots.
3. Use a lighter rake to remove the thatch from your yard. 

If your lawn looks yellowish after mowing, it could be a thick layer of thatch. Be prepared that your yard may look unsightly after dethatching, but over time, it will recover and flourish. You’ll need to dethatch once every two to three years. For more helpful information about thatching, and dethatching refer to this article. 

Final Thoughts

In summary, there are only a handful of reasons why your grass turns yellow after mowing.

Consider whether your lawnmower blade is sharp, whether you are removing too much grass when you are trimming, and if you have too much thatch build-up. Use the provided solutions to get your lawn back on track and looking healthy, green, and lush. 

An additional thought on yellow-looking grass: if none of the above suggestions seem to be resolving your issue, you’ll need to delve deeper into what might be causing your lawn to appear yellow.

Your lawn could be suffering from a handful of other issues and require different solutions.