Why is my compost forming balls?(and how to fix clumping)




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If you have peered into your compost heap to find lumps, or balls, of compost, you may have a problem. Don’t worry, there are some ways to fix this.

In short, it means there is too much moisture in your compost. It is also very common if you are using a compost tumbler. The rotating motion can compact the materials inside when it is too wet.

It can happen to compost in any medium though. Some compost ingredients are just more prone to sticking together. 

Quite compacted and large balls (golf ball-sized and bigger) of compost might never break down. This isn’t good for your compost because those lumps are then unusable. 

There are ways to fix and prevent compost clumping though.

So, below in more detail, we answer, why is my compost forming balls? (How to fix compost clumping). 


The biggest reason for compost clumps is moisture. So, don’t add more water in an attempt to break down the clumps. This only adds to the issue and may cause more balls to form in the future.

The moisture is a sign that there is too much green material compared to brown material. So, if you have been mainly adding food scraps, like fruits, vegetables, and eggshells – this all adds moisture. 

If the same kind of food scraps have been piled upon each other, then these are more prone to form balls. Settling occurs and compacts the material into a ball, with the aid of the moisture in your compost bin. 

These balls are then packed too tight for air to get in and decompose the materials. 

compost tumbler with balls of compost inside

Tumbler Composter Creates Balls

A tumbler composter is much more likely to create balls of compost than other kinds of systems. This is because of the rotating action. If the composition is already too moist, it will quickly lead to balls forming. 

However, compost created in any form may experience some clumping. As mentioned before, even a regular compost can form balls if there are moist scraps left to settle and form lumps. 

Why You Shouldn’t Use Compost Balls

The compost that has formed balls is normally not decomposed. The compaction of the materials means it is hard for air to get to the inside of the ball and therefore it can’t continue to break down.

So, that leaves you with balls of unfinished compost. If put on the garden in this form, it may be detrimental. During the breakdown process, the material is normally acidic, compared to pH-neutral finished compost.

This may be too much for some plants and it will damage them.

Check the Compost Clumps

However, sometimes finished compost can form balls too. It is a bit like regular dirt that can clump.

If your compost is finished but has formed some small balls, it isn’t a big deal. You can break these up to make them easier to use. 

Or, you might leave them as little lumps to slowly break down onto, or in, the earth. 

You will be able to tell if it is completely ready compost that has formed balls, or if it is still processing and needs your assistance. An unfinished compost ball will usually smell when you break open the lump. 

Use a shovel or similar to break open a lump. Check if it smells or if you can see chucks or material that is still breaking down.

If it is finished, you shouldn’t be able to recognize any components in the compost, it will just look like dirt.

On the other hand, finished compost looks like loose, dark brown soil. If this forms lumps, when you break them apart they will look the same inside and have no foul smell. 

How to Fix Compost Clumping

You fix compost clumping by addressing the moisture issue. So, to do this you will need to add more brown material to the mix. This can be paper, sawdust, dried leaves, cardboard, and cornstalks, to name a few. 

This will help balance the content of water. However, if you have identified the lumps in your compost have definitely not finished decomposing, you need to break them up.

Use a shovel or rake to pull apart the clumps so that air can get to them.

Now, the lumps should have a chance to begin decomposition again and the added brown material should mean the moisture won’t get out of hand.

However, keep an eye on it as it can take some time to get the balance of brown and green material right. 

Additionally, you may want to put the compost bin out in the sun temporarily to reduce the moisture. Or, if it isn’t portable, remove any cover to allow some moisture to evaporate. 

How to Prevent Balls of Compost From Forming

Of course, prevention is always better than cure. So what can you do to prevent compost clumping in the future?

Layering is the answer. If putting too many green materials contributed to the compost balls, then ensuring there are layers between the green waste is the way to control this.

So, you add a layer of green waste like your vegetable scraps. Then, you would also add a layer on top of that of brown materials, like shredded cardboard or newspaper. 

If you ensure that this layering process is followed, the moisture should be absorbed by the brown material and it adds some room for air to move around.

This is essential for the decomposition process to be able to continue and it should reduce the risk of balls forming.

Improve Your Tumbler 

As mentioned, the rotating motion of a tumbler can lead to compaction and a higher chance of balls forming. A solution to this is that some tumblers come with spikes on the inside that break apart the compost as it turns. 

However, if you have already purchased a tumbler compost and it doesn’t have spikes then there is an alternative solution.

You can add rocks to the tumbler that will break up the compost as it turns. It may not be as effective as spikes, but it will help.

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