Lawn Mower Not Mulching Properly? How to Fix It

You’ve bought into the whole idea of mulching your clippings instead of bagging them. All of those benefits for your lawn, the planet and your finances. You get the mower out, start it up and wait to see the magic. But your lawn mower is not mulching properly – what the hell?? There are clumps, there’s a trail of oversized clippings…that’s not going to break down and feed your lawn – it’s going to attract lawn fungus and pests. Whoa! You can stop freaking out now. A lawn mower that is not mulching properly is a problem that is often very easy to remedy, with some minor modifications, which I’m going to explain in this post.

The most common causes of a lawn mower not mulching properly are a damaged or dull mower blade, having the wrong sort of blade installed, a clogged cutting deck, having the cutting deck set too low and trying to go too fast.

Clear Symptoms of a Lawn Mower that is not Mulching Properly

When a lawn mower is mulching your grass properly, you should barely notice the clippings that are left behind on your lawn. That’s how fine they should be. So when it’s not mulching properly, the signs are very clear cut. You’ll probably notice the following.

Mulching Mower Leaves Clumps

You look behind your mower, expecting to see nothing more than a light dusting of finely ground clippings, but instead, you see huge clumps of clippings that resemble something like what you’d expect to see in a field full of cows.

Clippings that are clumped together is a sign that your lawn mower is not mulching properly or you’re doing something wrong. It’s also a sign that you need to fix the issue, as clumps of half-mulched grass clippings are a haven for things like lawn fungus, and prevent sunlight from reaching the grass underneath too, which can end up killing it.

Clippings that are Too Big

Clumping is not the only way of looking at the clippings left behind to determine if a mulching mower is working or not. If the clippings that are being left behind on your lawn are not too different to those that are deposited into your grass catcher when you bag, your mower isn’t doing its job. The clippings need to be much more finely chopped than that.

Mulching Mower Leaves a Trail

I’ve never actually had this happen to me, but I did once have a neighbour that couldn’t for the life of him figure out why every time he mulched, his mower was leaving a trail of clippings down one side of each pass. We did eventually get to the bottom of this, but it took quite a bit of head-scratching. I’ll get to how we fixed it in a moment.

Common Reasons Why a Lawn Mower Might Not Be Mulching Properly

There are several reasons why a lawn mower might not be mulching properly, some to do with the mower itself and others to do with conditions or your mowing technique. I’m going to outline a few parts of your mower that you might want to check.

You’re Using the Wrong Type of Blade

This is a super rookie error, but have you definitely checked that the blade you’re using on your mower is a mulching blade? Using a different type of blade will not produce the conditions needed to effectively mulch. Mulching blades vs regular blades, for example, are very different. Mulching blades feature a much longer cutting edge and a curved design that maximizes the blade’s contact with clippings, and circulates the clippings around the deck rather than discharges them. A regular blade on the other hand is much straighter and aerodynamic in design, creating more lift (suction effect in the deck), and is designed to cut and discharge the clippings far more rapidly. The same thing goes for mulching blades vs high lift blades; they’re not designed for the same purpose.

So make sure that you actually have a mulching blade fitted, as other types of blades just aren’t capable of mulching.

The Blade is Dull

If the cause behind a lawn mower not mulching properly is a fault with the mower itself, this is probably the most likely culprit. A mulching blade needs to be sharp enough to do its job. If it’s on the dull side, clippings won’t get chopped up into mulch. You’ll likely see clippings that are much too large. (Here are several more ways how you can tell if your mower blade is dull).

The solution to this is very simple: sharpen your blade. Actually, before you take the time to sharpen it, inspect it first. If it’s an old blade, is it corroded? Does it have lots of nasty nicks and dings? If you do spot any of these things, you might want to get a replacement blade instead. New blades don’t need to be sharpened – you can just fit it and get to mowing straight away.

Your Mower Deck is Clogged

A lot of people think that the only part of a lawn mower that matters is the blade. But that’s not true. It’s very, very important that the cutting deck is kept clean and in good condition. With mulching, the clippings need to be circulated around the deck numerous times to be finely mulched, but a clogged or damaged deck will result in the airflow and circulation being far less effective.

So turn your mower over and have a look at the deck. Are there loads of dried on clippings clogging it up? If so, grab a scraper and get them off. If you don’t see anything clogging the deck, check for damage. Are there any cracks, holes or corroded areas? If so, this needs to be fixed. It could very well be the reason your lawn mower is not mulching properly.

Your Mower Isn’t Powerful Enough for Mulching

Can you put a mulching blade on any mower and expect it to mulch well? NO! But just like the issue of people using the wrong blades when mulching, this is another common mistake. If you put a mulching blade on a mower that isn’t designed to mulch, it’s very likely that it’s not going to do a good job.

Mulching mowers generally have deeper decks, which helps with recirculating the clippings, and they’re also usually equipped with a stronger motor/engine, as the mulching process requires that extra oomph.

Your Mulch Plug Isn’t Fitted Properly

This was the answer to the problem that had me and my neighbour scratching our heads for weeks on end (yeah…we’re not that clever). If you’re noticing a trail of clippings left behind on one side of your mower, it’s highly likely that your mulch plug isn’t seated properly. There’s a small gap on one side that unmulched clippings are “leaking” through and leaving a trail. This gives the impression your lawn mower is not mulching properly, but it’s a 5-second job to properly seat the mulch plug and TA DA…problem solved.

There Might Be NOTHING Wrong with Your Mower

That’s right. You heard me. Even though your lawn mower is not mulching properly, there might be nothing wrong with the actual mower itself. It might be YOU or the conditions that is the problem. It’ll make sense in a moment.

You’re Going Too Fast

One thing you have to realize when you’re mulching vs bagging, is that your mower is having to do a lot more work. After all, you’re asking it to cut the grass into minute size clippings rather than the regular sized clipping that are deposited into the grass catcher and then discarded.

All that extra work takes time (the grass must be put through the cutting cycle several times), which means if you are zipping around your lawn at normal pace, it can seem like your mower isn’t mulching properly. The problem is that you’re not giving it time to mulch properly.

Solution: When you’re mulching your grass, be prepared to mow at half your regular pace. This extra time will allow the blade to have much more contact with the clippings, resulting in a finer mulch at the end.

You’re Mulching Too Much Grass at Once

This is another very common error when mulching (well…when mowing in general to be honest) that can give you the feeling that your mower isn’t working properly. You look outside and see that your lawn is pretty overgrown. You haven’t been sticking to your lawn care plan (naughty, naughty). And you decide today’s the day that you’re going to whip it into shape, and you’re going to mulch it too.

You set the deck at a height that means you’re going to be taking several inches off at once. BIG MISTAKE. Never cut more than a 3^rd of your lawn’s height at once. A) It’s bad for the lawn and B) it’ll cause your mower to clog, especially when mulching.

The volume of clippings that will be circulated around your mower’s deck when you do this will be overwhelming. Your mower’s engine or mower will strain under the pressure and there will be too much grass for your blade to do a good job.

Solution: Only mulch a 3^rd of your lawn’s height at once. And maybe even move your mower’s cutting height one or two notches above that for the first pass, and then move it back down and do a second pass.

You’re Mulching in Wet Conditions

Cutting damp grass is bad enough when you’re bagging the clippings. But when you’re mulching and the lawn is wet, it’s a recipe for disaster. Wet grass sticks to ANYTHING and is especially fond of sticking to other pieces of grass. Clumping is a necessary evil when mowing in wet conditions, but it can give you the feeling that your mower isn’t mulching properly.

Solution: Want to know how to keep grass from clumping when mowing? It’s a simple fix (unless you live in the UK)…try mulching your lawn when it’s dry. You’ll likely notice that the issue disappears immediately.

Related Article: How to Keep Grass From Sticking Under the Mower Deck

Lawn Mower Not Mulching Properly: A Quick Action Plan

In a lot of cases, a mulching mower that appears to not be working properly can be remedied very quickly, either through adjusting the way that you mow or by making small tweaks to your mower.

First Things to Check:

• You’re using a lawn mower that is designed to mulch clippings
• You are using a mulching blade

Next Round of Things to Check:

• Are you trying to mulch too much grass at once? Try raising the cutting deck to the next notch.
• Are you mulching when it’s wet? If so, try waiting until it’s dry.
• Try mowing slower. Slow and steady wins the race when it comes to mulching.

Final Checks:

• Is your blade dull? If so, sharpen or replace it.
• What about your deck – is it clogged or damaged? Then clean it or repair it.
• Noticing your mulching mower leaves a trail? Reseat the mulch plug.

If you do all of this, you should definitely notice an improvement in mulching performance. If it still seems that your lawn mower is not mulching properly…it may be that it’s just not that good! Time for an upgrade?