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Why Does My Worm Bin Smell? Causes and Troubleshooting Steps

Why Does My Worm Bin Smell? Causes and Troubleshooting Steps

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Paul Brown

When you choose to vermicompost indoors, you become very conscious of changes in smells coming from your worm bin. An earthy smell is normal. It’s not offensive. But when you open the lid and a pungent odor hits you so hard that you lose balance, you have a serious problem beginning. This happened to me about three weeks into my vermicomposting adventures and I thought I was going to have to give it up completely. There was no way I was keeping something that smelled like that in my house. But fortunately, I read a lot of literature and realized that this is a common issue caused by a few missteps that are easy to correct.

Why do worm bins smell? The most common cause of smelly worm bins is excess moisture, usually from a combination of too much watering and too many water-rich foods. Other causes of odors in worm bins include rotting food, dead worms, or lack of adequate ventilation.

Let’s dig through the bin and address each of these individually so that we can determine exactly what’s causing that smell.

Worm Bin Smells Caused By Excess Moisture

If there is one issue that is most likely to cause a worm bin to smell, it’s excess moisture. Think of the issues that excess moisture causes in homes: mold and mildew… and the smell that comes with it. Water is a critical element for worms but too much causes problems. In fact, excess moisture in the bin can prevent air from flowing effectively throughout the bin and cause anaerobic conditions within the bin (source). Having proper drainage is a key part of preventing this. So is having adequate air holes. But the primary thing that you have control of every day is how much moisture you are adding to your bin. And it is introduced in two ways:

  • Excess Watering
  • Too Many Water-Rich Foods

Excess Watering

If you are putting too much water in and it lacks sufficient drainage to take away the excess, water will begin to pool in the bottom of the bin. That pooling of water will become stagnant and anaerobic. Your worms can actually drown in this water because it lacks oxygen. But the point here is that the water will begin to cause the bedding to smell. And the longer it sits, the worse the odor will be.

The solution to this is to correct the drainage issue. Your bin may need more holes in the bottom or it could be that the wet cardboard and paper in the bottom of the bin have become so saturated that they are pressed down over the holes and sealing them. You may need to remove the bottom couple of inches of bedding if it is severely oversaturated.

Too Many Water-Rich Foods

A lot of the fruits and vegetable scraps that are so great for worm bins are very water-rich. If you are putting in more than the worms can eat, the excess moisture will slowly build up. Again, proper drainage can minimize this problem but putting more food in than can be consumed just results in moldy, rotting foods and more odors.

Make sure that the food is being eaten (or mostly eaten) before adding more. If the moisture is building up, it’s okay to stop feeding for a few days while you get the bin back into balance. Then, introduce water-rich foods in smaller quantities and judge future amounts by how much they are eating.

Rotting Food Causes Worm Bins To Smell

There is a lot of misconception about rotting food when it comes to worm bins. The truth is, worms depend on some level of decay for larger food items to become small enough that they can consume them. Red wiggler worms don’t have teeth so your kitchen waste becomes an easier meal as it breaks down.

But when too much food (or the wrong kinds of food) are left in a bin to rot, they can cause very unpleasant odors.

This takes us back to managing how much food is placed in the bin at a time. Too many people think of their worm bin as a wastebasket. It needs to be managed a little more carefully than that so that we don’t create a stinky pile in a box. Avoid meats and dairy. Their odors are downright offensive when they spoil and will attract rodents which can lead to further issues.

Do Dead Worms Smell? Yep!

Remember that “earthy” smell that I mentioned which comes from a healthy bin? Well, that’s the opposite of this smell. One or two dead worms in your bin aren’t going to cause an issue and it’s a natural cycle that will take place in the ecosystem of your bin. But when you have a lot of worms die in a short period of time it can give off a rancid odor that smells pretty much like you would think dead worms smell.

There are two steps you need to take with this one.

  • First, remove all of the dead worms that you can find. It may be necessary to pull out sections of bedding and sift through it one at a time.
  • Next, we need to figure out exactly what has happened. Why have those worms died?

Were they clustered together or were they spread out throughout the bin? If they were spread out, it may indicate an issue with the bedding itself. If clustered, were they submerged in water or surrounding a certain food item? It’s important to look for clues here. Your goal is to determine why the worms died and eliminate that issue!

Lack Of Ventilation Doesn’t Prevent Odors, It Causes Them!

I spoke with someone recently who was interested in creating a DIY worm bin but didn’t want to add air holes because they were afraid it would smell and they were concerned about the worms escaping. The truth is, worms are not likely to leave their bin if they have what they need. And one of the things that they must have is oxygen. Air holes provide a way for fresh air to come into the bin. Air holes also serve other purposes including helping to keep the moisture levels in check.

But here is the other issue with not having enough ventilation. Lack of a fresh oxygen source causes the aerobic conditions in your bin to turn anaerobic, just like that stale water does when sitting in the bottom of the bin. No oxygen = anaerobic conditions. And that means foul odors.

Make sure that you have plenty of air holes to allow fresh air into your bin. Your worms will be healthier and your bin is actually less likely to smell.


A worm bin that smells likely means that you have one or more of these issues. Troubleshoot them one by one and see if you can identify what area needs correcting. Once you know where the issue is it is pretty easy to solve these and you can get rid of that smell in your bin.

Vermicomposting shouldn’t be a hassle. There are just a few simple principles that you need to be following. Read through our vermicomposting articles and bookmark us for any future issues!