A woman scrapes veg scraps into a compost bin.

How To Stop Indoor Compost Bins From Smelling

You can minimise or eliminate the smell of indoor compost bins, if you take the right steps. Fortunately, it’s not hard to produce indoor compost without stinking your kitchen out. In this article we’ll cover everything you need to stop your compost from becoming smelly.

I’ll be honest, I’m not allowed to compost in the house. My wife and I have very different views on what’s acceptable, and while I can do what I want in the garden and greenhouse, I am banned from composting in the kitchen – other than a small compost caddy which I am expected to empty daily.

Fortunately, I have a garden to compost in, and use a greenhouse for micro-composting, so that’s not really a big deal. But while everyone has waste, not everyone has the space to compost outside.

Fortunately, it’s perfectly possible to compost inside without causing a nasty smell – in fact, in my recent experiment with micro-composting the only smell I got was a faint citrus smell, only detectable when I opened the top of the bin.

What causes compost to smell?

Of course, compost can smell if you get it wrong. Ideally, our waste is turned into compost by aerobic (i.e. with air) organisms, which can turn waste into compost with limited smell. But if conditions are not right, anaerobic organisms take over, creating unpleasant smells in the process.

Let’s take a look at what can cause your compost to smell – and what you can do about it.

Not enough ‘browns”

Every compost heap should have a mixture of greens and browns.

(Greens here refer to things which are high in nitrogen, such as kitchen peelings, vegetable waste and most foods. Brown refer to things which are high in carbon, such as old newspaper. For more on the science, see Compost Chemistry on the Cornell University website.)

Don’t worry too much about the exact ratio. The things you put in will all have different levels of nitrogen and carbon, different masses e.t.c. and unless you want to have a calculator out every time you put something in your compost bin it’s not worth worrying about. Just aim for a roughly even mix, or ideally slightly more greens than brown. If it does get smelly, try adding some more browns.

When you have the right number of greens and browns, if you have the time you are better mixing them together rather than adding them in layers.

Not enough air

To compost properly, the microbes in your compost heap need air. Without at least 5% air, the aerobic (‘with air’) bacteria can’t function. With my recent experiment, I started off by mixing the compost around my bin on a regular basis to introduce air, and ensured the microbes had enough oxygen to do their job.

Mixing it every couple of days is ideal. And with a small compost bin, mixing is easy and quick.

But if you don’t want to mix, another alternative is to introduce ingredients into the compost that create air pockets – scrunched up cardboard is ideal for this.

Too much water

One cause of a lack of air in the compost bin can be too much water. The water soaks the particles and fills up those air gaps, stopping oxygen from reaching the bacteria in the compost. You then get anaerobic (‘without air’) bacteria, which create an unpleasantly compost smell. (It also takes longer!)

Ideally, you’ll have a tap on your compost which will allow you to drain off the liquid or ‘compost tea’. This is valuable in itself – you can then dilute this down with water and add it to your plants as a fertiliser.

You can also add ingredients that will help soak up the water. Examples included shredded paper (not too much, though, as it can turn into a sludge), a little newspaper or cardboard to soak up the water.

You don’t want it completely dry, though – those aerobic organisms do need some water to get to work. In an ideal world, the consistency of the material will feel like a wrung out sponge.

The wrong type of foods

All foods can be composted, but foods like dairy, meat and fish (both cooked and uncooked) are a little bit ambitious for an indoor system – unless you are using a system designed to handle it, like a Bokashi bin.

Large pieces of waste

The smaller the pieces in a compost bin, the easier it is for the bacteria to work on it. That’s because the surface area of the material is larger. If your bin is too smelly, try putting smaller pieces in.

No soil

Your food waste needs bacteria to break it down. So if possible, add a few handfuls of soil to your compost, or put a thin layer of soil at the bottom of the compost bin. This helps introduce the bacteria that you need to compost, getting the whole process going nicely.

Lack of Bulking Agent

Bulking agent is the magic ingredient for compost that no one ever talks about. Materials like wood-chips, leaves and sawdust create air pockets in the compost, ensuring bacteria have sufficient oxygen. More importantly for this post, the microbes that live on bulking agent are great for odour control. If you do have an odour problem, adding a layer of sawdust on the top of your compost will quickly remove the smell.

Do ensure that any bulking agent is completely dry before adding it!

Odourless bins

You can also buy compost bins for use which are built specifically to combat odour.

Some bins use a charcoal filter in order to absorb smells. This is a great idea for compost caddies and for collecting cooked food.

If you’re brave enough to share your home with dozens of ‘red wriggler’ worms, you might consider having a worm compost bin. Compost worms, usually the ‘red wriggler’, not only help break down the material, they can also remove diseases like E-Coli!

Finally…

Whether you have a garden or not, it’s well worth doing your own composting.

Composting rapidly decreases the volume of waste. It also creates a valuable material that you can use for house plants and herbs, and good home composting does without causing damage to the environment. And when you have your finished compost, you have the satisfaction of having turned food waste into ‘black gold’, reducing landfill and saving money at the same time.

Happy composting 🙂

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