Is It Okay to Compost in an Airtight Container? 

For homeowners who want to start composting indoors, a common first instinct is to start composting in an airtight plastic container. The reasoning behind this decision is usually that keeping the compost airtight will reduce foul odors associated with composting.

Composting should not be done in an airtight container because this induces anaerobic versus aerobic decay. Composting without oxygen leads to putrefaction that causes the compost to stink and process slowly. With access to air, the smells associated with the compost should be minimal.  

Making sure compost has access to aeration is an important part of keeping a tidy compost bin. Read on to learn more about aerobic composting and why you can’t compost in an airtight container successfully.

Compost Needs Airflow

Even though an airtight container seems like a good idea to keep indoor compost from smelling up the house, this actually has the opposite effect. Here are the reasons that compost needs airflow: 

  • Smell: Without aerobic bacteria, compost generates methane, ammonia, and other smelly by-products while it breaks down. This means anything allowed to rot in an airtight container will smell especially bad if the bin is opened. 
  • Speed: Anaerobic decomposition is much slower than aerobic decomposition, which means without access to fresh air, compost takes longer to break down into a usable form. The heat generated by aerobic composting also helps the compost to break down more quickly, which means it can be reincorporated into the garden faster too. 
  • Pathogens: A major disadvantage of anaerobic composting versus aerobic composting is that anaerobic composting doesn’t reach temperatures high enough to kill off dangerous pathogens. Once introduced back into the garden, these pathogens can lead to plant disease or even human illness. (Source: Washington State University)

Adding oxygen to compost isn’t just a matter of practicality. It’s also the safest composting method for reducing the transmission of disease. This means that airtight containers for composting won’t cut it without some kind of rigging for air access.

Is Composting Aerobic or Anaerobic? 

Composting can be either aerobic or anaerobic, depending on whether air is introduced to the compost during composting. Aerobic means “with oxygen”, and anaerobic means “without oxygen”. So composting performed in an airtight container would be anaerobic composting. This results in the following: 

  • A much slower decomposition rate
  • The release of greenhouse gases into the atmosphere

Anaerobic composting isn’t usually recommended since it isn’t environmentally friendly, and it smells a lot worse than aerobic composting. The slow decomposition rate also means that it takes compost forever to break down into a state where it can be used for soil enrichment.

How Much Air Does Compost Need?

The good news for indoor composting is that even if you want to keep a compost pile inside, the compost doesn’t need a ton of air. If it is turned every few days, cutting holes in the top of your airtight container should allow enough oxygen exchange to encourage the aerobic bacteria to multiply. 

While there is no hard and fast rule for how much oxygen an indoor composting container should get, the smell of the compost is a good indicator. 

If the compost takes on a smell like rotten eggs, this means that methane and acids from anaerobic composting have built up from lack of oxygen. More oxygen should be introduced by turning the compost or adding more holes to the container.

How Often Should You Aerate Your Compost? 

Compost should be aerated every few days to make sure that the pile is composting evenly. Fresh compost can also be added to the bin periodically, and the compost should be aerated when new compost is added. 

Here are a few of the ways you can add aeration to your compost bin (Source: Home and Gardens TV): 

  • Add holes. Adding more holes to the bin itself will naturally allow air to pass through the bin, giving the aerobic bacteria plenty of ventilation.
  • Add a PVC pipe for aeration. Adding a PVC pipe down through the center of your compost bin can help the interior of the compost pile receive oxygen as well as the outside. This can help aerobic compost break down faster.

  • Turn the compost pile. Every few days the compost pile in the bin should be turned over and stirred up. This allows compost on the bottom of the pile to access oxygen and ensures that the compost breaks down evenly.

Making sure that the compost container is getting enough air is a major part of making sure the compost works like it’s supposed to, so it’s worth the effort to keep it oxygenated and fresh.

What Happens When Compost Has No Oxygen?

When compost doesn’t have access to oxygen, this means that any bacteria that require oxygen to live will be killed off. This leaves anaerobic bacteria, which can still break down organic compounds at a slower pace, but also produces the following unwelcome by-products: 

  • Methane: Methane has a stench that anyone who smells it will associate with rotting garbage, methane is a harmful greenhouse gas. Anaerobic composting in landfills make up the third-largest source of greenhouse emissions in the United States. (Source: American Chemical Society)
  • Carbon dioxide: In aerobic composting, carbon dioxide is also generated, but it is in small enough amounts to be absorbed by environmental vegetation. The carbon dioxide given off by anaerobic composting is much greater in comparison. 
  • Ammonia: Along with having a pungent unpleasant smell, ammonia is also harmful to human eyes and respiratory tracts in large doses. 

The generation of greenhouse gases by an anaerobic composting bin means that not only will the compost smell a lot worse than it needs to, it’s also counteracting many of the environmental benefits of using a compost bin in the first place.

Best Containers for Indoor Composting

For a homemade indoor composting bin, one of the best containers is a plastic storage bin with a clip-on lid that has holes drilled in it for aeration. This bin should be at least eighteen gallons to provide enough space for the compost to be turned easily. 

Here are a few tips for choosing the best container for indoor composting and using it correctly (Source: The Spruce): 

  • Go with plastic. Organic materials like wood can suffer from water damage and rot when they come into contact with decomposing materials in the compost. Non-reactive food-safe plastics are the best type for composting. 
  • Make to include lots of holes. Drill aeration holes one to two inches apart to encourage even aeration across the entire composting bin. Limiting holes to the lid of the bin or to the upper section of the sides will allow composters to shake the compost bin gently to aerate it without leaking any liquids out of the sides. 
  • Set the compost outside. If you want to keep your compost bin indoors most of the time and keep indoor aeration of the bin to a minimum, plan on leaving the compost outside with the lid off once a week after stirring to allow oxygen to enter the bin. 
  • Add drying or “brown” materials to wet compost. If your kitchen compost contains too many wet materials like leftover vegetables and fruits, adding sawdust or mulched dry leaves can reduce any smells associated with wet compost and can help the compost break down faster. 

Composting isn’t complicated, but knowing the biological processes behind how compost works can help people understand how to get the most out of them.

Composting Is Better With Air

Composting in an airtight container is possible, but without oxygen, composting will take a long time to break down any organic materials and it will smell terrible in the process. Properly aerating compost is a much more effective and safe method for composting whether you’re doing it indoors or outside.

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