How to Fix Smelly Compost in a Compost Tumbler or Bin

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Stinky, slimy compost doesn’t have to end in failure. It can be fixed! Here’s how to fix smelly compost and how to prevent it from happening again.

fix stinky compost
Fixing Stinky Compost in a Tumbler.

We’re trying to do the right thing by composting our food scraps. However, some serious compost bin neglect over a few stressful months meant our compost ended up as a black, slimy, putrid, stinking mess.

Luckily, it’s easy to fix smelly compost.

To fix slimy, stinky compost in a tumbler, add dry material like brown leaves or straw and then turn the tumbler a few times each day until the moisture balance is right again. A handful of dolomite can also help reduce acidity and sweeten the smell.

That’s the short answer, but let’s break down why the compost in your tumbler can start to smell bad, so you can easily fix it and prevent it from happening again.

Stinky Compost Problem 1: Your Compost is Out of Balance

adding dry materials to fix stinky compost
Adding brown matter to smelly compost

When your compost is out of balance with too many wet ingredients like kitchen scraps and not enough brown ingredients like dried leaves or cardboard, your compost won’t decompose properly, causing it to smell.

The right balance is a ratio of 3:1 dry to wet ingredients. So three parts dry matter to 1 part green scraps. You can definitely go all science-y with this, but it’s not necessary.

To make the compost ratio easy, for every bucket of kitchen scraps, add a bucket or two of dry or brown materials.

Brown compost materials can include cardboard, shredded paper, egg cartons, toilet rolls, dry leaves, dry grass, straw.

If you live in an apartment or townhouse as we do, finding enough brown materials to add to your compost can be difficult. While technically shredded paper is a dry material, it tends to get wet easily and clump together, not really helping with the composting process.

We ended up investing in a bag of straw (actually sugar cane mulch because Queensland) to get the right balance in our compost bin. It’s a small cost to keep our scraps out of landfill.

Stinky Compost Problem 2: Not Enough Oxygen

The composting process relies on oxygen, among other things, to break down the ingredients and turn them into beautiful rich compost.

The problem with sealed compost bins like tumblers is that they prevent oxygen from getting to your compost. With no oxygen, your scraps don’t turn into compost; they turn into a putrid, smelly clump of yuck instead.

If you have a compost tumbler, it’s important to give the tumbler a couple of turns at least once a week.

This will aerate your compost, helping it to break down while preventing it from turning it into sludge.

If your sludge has turned into one big yucky clump, you may need to break it up a bit with a strong stick. It’s a good idea to wear a mask when you’re doing this.

To reduce the acidity of putrid compost and sweeten the smell add a handful of dolomite, garden lime or wood ash. I’ve found dolomite to be very effective at reducing the smell of neglected compost.

Stinky Compost Problem 3: Your Compost is Too Wet

stinky compost that is too wet
Wet, stinky compost. Mmm, rotten egg smell.

Not only does have the balance wrong cause wet compost, but rain getting into your compost tumbler can also cause your compost to become too wet. And wet compost becomes smelly compost.

If your compost has become too wet, it’s a simple matter of adding more brown matter to absorb some of the excess water and giving it a good turn to mix the compost.

After heavy rains, you may want to leave the lid off during the day when it’s sunny and not raining for two or three days to let your compost dry out. Just remember to put the lid back on at night to prevent dew and pests from getting inside.

Stinky Compost Problem 4: You’re Adding The Wrong Ingredients

Some things don’t work well in the compost bin.

Make sure you NEVER put in your compost:

  • dairy
  • meat
  • bones
  • animal fats
  • vegetable oils
  • pet poo
  • processed food scraps
  • bread, cake etc.

These ingredients will definitely make your compost smell bad.

If you want to compost ALL of your kitchen scraps, including things like bread and pizza crust and old bits of cheese, you might want to consider a bokashi bin.

Bokashi bins don’t compost as such; they use microorganisms and an anaerobic environment (no oxygen) to ferment foods. These fermented foods can then be safely added to a regular compost bin.

For more information, check out the post: Everything You Need to Know about Bokashi.

Stinky Compost Problem 5: Lack of Microorganisms

Organic matter is broken down by a whole host of beneficial microorganisms.

The problem with compost tumblers and other compost bins is that they are sealed and off the ground, so microorganisms have a hard time getting in to digest all your scraps.

If you’ve tried the above measures to fix your stinky compost and they haven’t worked, adding some microorganisms to your compost might do the trick.

You can add microorganisms in one of two ways. You can add some compost-rich garden soil to your compost bin to liven it up, so to speak.

Or you can add some bokashi organisms to your compost bin. You can buy bokashi (also called compost additive) at your local hardware store or garden centre.

How to Prevent Smelly Compost in the Future

Composting doesn’t take a lot of care and attention, but it does suffer from complete neglect, as I found out.

Here are five things to remember to avoid smelly compost in the future:

  • layer in dry ingredients every time you add kitchen scraps
  • give your compost a turn every week
  • leave the lid off for a day in the sun to dry out after heavy rain
  • don’t add animal products and processed foods unless they have been well fermented in a Bokashi first
  • add a handful of compost-rich soil now and then to enrichen it with living organisms.

But even if you do neglect your compost, you can rest assured that all is not lost – you can fix stinky compost with a little tender loving care.

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