Does Compost Smell? (The Truth About Smelly Compost)
When I first started composting, one of my biggest concerns was that it would stink. But by following the right composting rules, you can have an odor-free compost bin without much difficulty.
Does compost smell? A correctly maintained compost bin shouldn't give off much odor. If you find your compost smells strongly like ammonia, rotting eggs, or sickly sweet, then something is off balance. Luckily, some minor adjustments can help to bring it back on track.
In this article, I'll explain what a compost bin should smell like. I'll help you to troubleshoot some common smells, which could be telling you that something is off with your compost. Most importantly, you'll learn what can make compost smell and how to get rid of it.
Does a Compost Bin Smell?
All compost bins do give off a little odor. After all, they're full of decomposing kitchen scraps and plant matter! But if your composter is excessively smelly, then there are some things that you can do to get it back under control.
Usually, composting is just as easy as taking out your garbage. You can just walk your kitchen scraps to the composter every day or two, and not worry too much about correctly balancing its contents. Most people mix in yard waste like grass clippings in the summer or dead leaves in the autumn, which helps balance things out.
But sometimes the contents of your composter can build up the wrong proportions of ingredients, which can result in all kinds of unpleasant smells.
As a quick reminder, composting works best when you have the right balance of brown materials and green materials. Brown materials are carbon rich things like dry leaves or small branches. Green materials are nitrogen rich materials such as wet grass clippings, green leaves and food scraps.
What Should Compost Smell Like?
A healthy compost pile shouldn't have a bad smell to it. It should basically have a pleasant earthy smell like dirt.
If that's not the case, then something is likely going wrong with it and it will need to be adjusted.
The one exception to this is if you're composting pet waste or manure. Some composters are designed to handle these materials. However, they will still give off more smell than a composter that doesn't contain these materials. If you're composting animal waste, you can reduce the smell by adding extra newspaper, leaves, or straw to it.
What If My Compost Smells Sweet?
If you find that your compost pile smells sweet, it’s possible that there isn’t enough oxygen in your compost. This is quite common when you have a lot of grass clippings in your compost. (we’re talking about sickly sweet smells, not a smell like ammonia - see below for ammonia smells).
Compost piles need the right kind of bacteria and other microbial life to help break down organic matter. These bacteria are known as “aerobic”. In other words they need oxygen to survive.
A sweet smell can be emitted by organic acids as grass begins to decay and there’s a lack of oxygen. In other words “anaerobic” bacteria have taken over the decomposition process (this is the method that farmers use to make silage!). Aerobic bacteria love materials like grass clippings and they become active very quickly. But in doing so they use up all the available oxygen. The compost starts to warm up and becomes more compact. This means that the flow of oxygen is limited because there isn’t enough structure for air to circulate.
The problem is that this anaerobic decomposition process is slower and obviously much more smelly!
Here are some solutions you could try:
A huge pile of grass clippings can be wet and heavy. For particularly damp compost, it might be difficult to turn your compost pile. In that case, you can create a few holes in your compost pile and fill them with dryer more structural materials like shredded cardboard instead. As they start to break down, your compost will balance out and become easier to turn again.
Another reason for sweet-smelling compost that shouldn't be a reason for concern is if you find you're adding a lot of fruit to your composter. If you have a lot of banana peels, apple cores, and other sweet-smelling fruit that you're putting in your composter, it may naturally give off a sweet smell for a few days. This is just the fruit breaking down and releasing its ethylene gas, and isn't a cause for concern if your compost otherwise looks okay.
What If My Compost Smells Like Ammonia?
A composter that smells like ammonia probably has too much nitrogen. I always try to find the right balance and not add too many green, nitrogen rich materials to my composter. Ultimately it comes down to experience and you'll develop a feel for what your compost pile needs.
The ammonia smell is caused by the excess nitrogen being released into the air.
To fix a composter with too much nitrogen, the solutions are similar to the list above. You can add brown materials like cardboard, sawdust, straw, or peanut shells. This will add extra carbon to your compost to help balance out the nitrogen. Other brown materials like twigs can help the structure of the compost.
If the smell is really bad and you want a quick solution, you can spread your compost out on a sunny day to allow the ammonia to evaporate more quickly. Frequently turning your compost will have a similar effect and is less messy, but may take longer.
What If My Compost Smells Rotten?
One of the worst smells that your composter can give off is one of rotten eggs.
If you find your compost has developed this smell, it means that there isn't enough oxygen available to allow aerobic bacteria to grow. Instead, your compost pile has become completely depleted of oxygen.
The rotten egg smell is a byproduct of smelly hydrogen sulfide from the mass of compost which has no air circulation.
Unfortunately to fix the smell, you're going to have to spend some time up close with your compost pile !
Turning your compost pile regularly loosens it and adds in pockets of air to help aerobic bacteria thrive. The bad-smelling anaerobic bacteria will naturally die off when there's oxygen in your compost again.
If you're turning your compost regularly but find it still has a rotten smell, then you may need to change the design of your composter. You can add a palette underneath or a bed of branches to allow for airflow from the bottom. You can occasionally add some layers of sticks and yard waste into your compost pile to give it support and create air pockets (imagine a compost lasagne !).
Odor Free Compost Bin
If you're looking for an odor free solution to composting, you might consider switching to a tumbler-style composter instead (link to Amazon). The big advantage of this kind of composter is the ease of turning. They also have a reputation for making compost more quickly, especially if you fill them in one go!
And they’re ideal if you have large quantities of grass clippings or soft moist materials. As you’ve seen above, too much wet, nitrogen rich material can cause problems with smells and reduces the efficiency of your compost process.
Big compost tumblers like this one on Amazon will produce compost more efficiently than a small one. In the past I’ve been able to reduce the size of grass clippings by half within a week if turned daily !
How Do I Get Rid of The Smell From My Composter?
OK… So we’ve seen a few reasons why your compost might smell bad. Good composting is a balancing act between the 4 essential compost ingredients: carbon, nitrogen, oxygen and water.
But your compost can get off-balance in several different ways. Here are the five big things to fix if you want to avoid smelly compost.
Your Compost Needs More Oxygen
A compost pile needs to be aerated regularly to give bacteria and other microorganisms the oxygen that they need to grow. They can't do their jobs if they can't breathe!
Make sure that your compost has good airflow. If you're using a tumbler-style composter, be sure to give it a turn every few days. If you have a traditional compost pile, you should turn it using a pitchfork regularly.
Adding structured materials to the compost can help increase airflow.
Your Compost Is Too Wet
If your compost is in a very shady and damp area, then it may get too wet. If the material in your compost gets too dense and matted, it can also hold too much moisture. Wet compost can lead to other problems too, especially a lack of oxygen.
Just like if your compost lacks oxygen, the best thing you can do to fix it is to turn the pile regularly. Try to turn your compost pile once per week or so until it starts to dry out.
If wet compost becomes a constant problem for you, consider relocating it to a different area of your yard that gets more heat and sun. Aim for 6 to 8 hours of sun per day for optimal results.
Your Nitrogen Is Off Balance
Either too much or too little nitrogen can lead to a smelly compost pile. It's all about making sure that you have the right balance of green (nitrogen-rich) and brown (carbon-rich) materials. A healthy compost pile should be a 50-50 mix of green and brown materials at most. 20% green materials and 80% brown materials is even better.
If you find that your compost gets too many food scraps and grass clippings, you can balance it out. Add some straw, shredded newspaper, or other brown materials and mix them in thoroughly.
You Added The Wrong Materials
Items like dairy, meat, animal fat, or oils should never be put into your composter (It’s not recommended unless you have experience with this and can run a hot compost pile). In addition to giving off more smell, they will also attract pests like mice and maggots.
Manure can be added to compost, but it will increase the smell. So try to do it in small amounts if at all. Manure can increase the ammonia smell of compost.
Not Enough Heat or Microbial Life
Compost piles will only work well in temperatures above 21° C (70° F.) Below this, your compost won't have the microbial life needed to break down plant matter.
If your compost seems too dry, spraying it with a garden hose to add some moisture can increase the amount of heat generated, and boost the bacteria that is present. Just don't get it too wet. Adding moist materials will also help.
In some cases, your compost pile may not have many microbes to begin with. In this case, try adding some soil from your garden to the composter to add the microbes it needs.
Some people also use a compost starter, like this organic version on Amazon, which helps speed up the compost process, helping to maximize the amount of compost you can make in a shorter amount of time.
A healthy compost bin shouldn't have a strong odor. In fact, it should have a fairly neutral earthy smell, or the way that grass smells after a rainstorm.
If your compost smells bad, that's a sign that something is off balance. Remember that compost is a living ecosystem that has particular needs.
Most of the time, composting is easy and you can simply dump in whatever kitchen scraps and yard waste as needed. But if your compost starts to smell, I always suggest that you look for the obvious reasons and try to fix them as soon as possible. See if your compost has too much or too little green matter (nitrogen-rich materials.) Check if there's too little or too much moisture too. And finally, be sure to aerate your compost regularly so that it's getting enough oxygen.
If you follow this guide, you'll have nutrient-rich soil to add to your garden in no time, without any of the bad smells!