How To Keep Compost From Smelling

  • By: Sam Richards
  • Date: August 31, 2023
  • Time to read: 10 min.

Composting is not just a modern-day fad; it’s an age-old method that has consistently proven its merits in sustainable agriculture and waste management. By converting organic waste into nutrient-rich humus, composting not only enriches our garden soil but also reduces the need for chemical fertilizers and minimizes the amount of waste sent to landfills. Moreover, it serves as a proactive response to global environmental challenges by helping to lower greenhouse gas emissions. While its benefits are many, there’s a ubiquitous challenge that many enthusiastic composters face: the unwelcome and often unpleasant odor from their compost piles or bins. Tackling this concern effectively requires an understanding of the composting process and some key best practices. Dive into this article to discover the science and solutions to keeping your compost aroma-free.

Understanding the Reasons Behind the Smell

Decomposition is a natural process, and with it comes a multitude of biochemical reactions. When organic matter breaks down, it’s acted upon by a diverse community of microorganisms, each playing its part in converting that material into a rich, earthy substance. However, not all these microscopic actors and their processes are scent-free.

Anaerobic bacteria, which thrive in low-oxygen environments, produce several compounds that are not particularly nose-friendly. Methane, hydrogen sulfide (which has a rotten egg smell), and other volatile organic compounds can be released when the composting pile is compacted or lacks sufficient aeration.

Furthermore, the type of waste you’re composting can significantly impact the smell. For instance, adding too many nitrogen-rich materials without balancing them with carbon-rich ones can lead to the production of ammonia, a sharp, pungent smell.

It’s essential to differentiate between the mild, earthy scent of healthy decomposition and the foul stench indicating that something in the composting process is off-balance. Recognizing and understanding these nuances will be your first step in addressing and preventing unpleasant odors in your compost.

Basic Compost Components

The art of composting might seem intricate, but at its core, it revolves around two primary categories of organic materials. These components work in tandem, providing the ideal environment for decomposition and the necessary nutrients for the microorganisms at work.

  • Greens (nitrogen-rich): Often referred to as “wet” or “nitrogenous” components, these are typically fresh or recently alive materials. They include:
    • Fruit and vegetable scraps: The peelings, trimmings, and expired pieces from your kitchen.
    • Coffee grounds and tea leaves: The remnants from your morning brew.
    • Fresh grass clippings: The result of mowing a lush lawn, rich in nitrogen.
    • Plant trimmings: Fresh cuttings from your garden. These materials are packed with the nitrogen necessary for microbial growth, facilitating the rapid breakdown of organic matter.
  • Browns (carbon-rich): These are generally drier, older materials that have been dead for a while. They play a crucial role in providing structure to the compost pile and ensuring that it doesn’t become too wet or compacted. Examples are:
    • Dried leaves: Often abundant in the fall, they provide bulk and are a rich carbon source.
    • Straw and hay: These agricultural by-products are excellent for maintaining a well-structured compost.
    • Cardboard and paper: Non-glossy types, shredded into smaller pieces, can be great carbon contributors.
    • Wood chips and sawdust: While they decompose slower, they’re valuable for their high carbon content.

Browns help to balance out the moisture and nitrogen provided by the greens, ensuring that the compost pile remains airy and less likely to emit foul odors.

For successful composting, understanding and integrating the right mix of these two categories is pivotal. They create the balanced ecosystem needed for efficient decomposition, resulting in a rich, loamy compost beneficial for gardens and plants.

Proper Ratio of Greens to Browns

Harmonizing the composition of your compost pile is analogous to cooking a well-balanced dish. Just as you’d adjust ingredients for the right flavor, composting requires a precise mix of nitrogen-rich greens and carbon-rich browns to promote healthy decomposition.

  • The Science Behind the Ratio: The diverse community of microorganisms breaking down your compost requires both nitrogen and carbon to thrive. Nitrogen acts as a protein source, fueling their growth and reproduction, while carbon serves as an energy source. For these microbes to operate at their peak efficiency, they need an appropriate balance of these two elements.
  • The Ideal Ratio: Although the exact ratio can vary depending on the materials used and local conditions, a general rule of thumb is to maintain a 3:1 ratio – that’s three parts browns to one part greens by volume. This doesn’t mean you need to meticulously measure every addition, but keeping this proportion in mind can guide your composting habits.
  • Consequences of Imbalance:
    • Too Many Greens: An excess of nitrogenous materials can lead to a compacted, soggy pile, encouraging anaerobic conditions. This can produce ammonia, giving your compost a sharp, pungent smell.
    • Too Many Browns: An overabundance of carbon-rich items can slow down the decomposition process. While it might not produce offensive odors, it can make your compost pile stagnant, taking longer to produce the desired rich, crumbly humus.
  • Adjusting On the Go: Composting is as much an art as it is a science. You might occasionally need to adjust based on observations. For instance, if the pile is too wet or smells of ammonia, add more browns. Conversely, if it’s too dry or not breaking down efficiently, toss in more greens.

In summary, while it might seem intricate at first, maintaining the right balance between greens and browns is crucial. By understanding the roles these components play and adjusting as needed, you can foster a thriving compost environment, reducing odors and producing quality compost more efficiently.

Aeration and Turning the Pile

Just as humans need oxygen to breathe and function efficiently, so do the beneficial microbes actively breaking down your compost. Ensuring ample oxygen supply through aeration is paramount for an odor-free and efficient composting process.

  • Why Aeration Matters:
    • Supports Aerobic Bacteria: Aeration fosters the growth of aerobic bacteria – the good guys in the composting scenario. These bacteria efficiently break down organic materials without producing foul-smelling by-products.
    • Prevents Anaerobic Conditions: Without enough oxygen, anaerobic bacteria take over. These bacteria can break down materials, but they do so much more slowly and produce methane, hydrogen sulfide, and other malodorous gases in the process.
  • Methods for Aeration:
    • Turning the Pile: This is the most straightforward method. Using a pitchfork, shovel, or a specialized compost turning tool, periodically mix the contents of your compost. This introduces fresh air, redistributes the materials, and breaks up compacted sections.
    • Vertical Aeration: Some compost bins are designed with vertical air shafts or tubes. These allow air to flow from the bottom to the top, providing consistent oxygen to the pile.
  • How Often to Aerate:
    • For backyard composting, turning the pile once a week is generally recommended. However, this can vary based on the size of the pile, the materials present, and the local climate.
    • If you notice your compost has a pungent, unpleasant smell or is overly wet, it’s a sign that you might need to turn it more frequently.
  • Benefits of Proper Aeration:
    • Speeds Up Decomposition: Regularly aerated compost piles decompose faster, turning kitchen scraps and yard waste into nutrient-rich compost in a shorter timeframe.
    • Regulates Temperature: Oxygen helps maintain the right temperature in the compost. A well-aerated pile will heat up, which aids in killing weed seeds and pathogens.
  • Potential Challenges:
    • For those with large compost heaps, turning might be labor-intensive. In such cases, tools like compost cranks or aerator wings can be invaluable.
    • In more compact urban settings, tumbler-style composters, which can be easily rotated, offer an efficient aeration solution.

In essence, aeration is the breath of life for your compost. Regularly turning and aerating ensures that your pile remains healthy, odor-free, and teeming with the beneficial microbial activity necessary for transforming waste into garden gold.

Maintaining Moisture Levels

Too much or too little moisture can be detrimental. Your compost pile should have the dampness of a wrung-out sponge. If it’s too dry, sprinkle some water. If it’s too wet, add more browns to absorb the excess moisture.

Layering Technique

Creating layers in your compost pile can optimize the decomposition process. Start with coarse, dry materials at the base, followed by alternating layers of greens and browns. This technique can improve aeration and hasten the decomposition process.

Using Compost Activators

Delving into the realm of composting, one might come across the term “compost activators.” These additives are like the kickstarters for your compost, giving it the initial boost to accelerate the decomposition process. Here’s a detailed exploration of these useful aids:

  • What are Compost Activators?
    • Compost activators are materials rich in nitrogen or microbes that assist in kickstarting the decomposition process. They can be natural, homemade, or commercially purchased.
  • Why Use Them?
    • Speeds Up Decomposition: If you’re looking for a quick turnaround from kitchen waste to compost, activators can cut down the wait time.
    • Revitalizes Slow or “Dead” Piles: Sometimes, compost piles seem dormant or inactive. In such cases, activators can reinvigorate the microbial activity.
    • Ensures a Healthy Microbial Population: A diverse and populous microbial community is essential for efficient composting. Activators can introduce or boost this community.
  • Common Natural Activators:
    • Fresh Manure: Horse, chicken, or cow manure is rich in nitrogen and can serve as a powerful activator. However, it’s vital to ensure the manure is from animals not treated with antibiotics or other medications.
    • Grass Clippings: Fresh grass clippings are a readily available nitrogen source that can jumpstart your compost pile.
    • Nettles and Comfrey Leaves: These plants are known to accelerate decomposition when added to compost piles.
    • Previous Batch of Compost: If you’ve already got a batch of well-decomposed compost, adding some to a new pile can introduce beneficial microbes.
  • Commercial Activators:
    • These are available at gardening stores and come in various forms, from powders to liquids. They often contain concentrated nitrogen and a mix of beneficial bacteria and fungi. While they’re effective, they might be more costly than natural alternatives.
  • How to Use Activators:
    • When starting a new compost pile, layer your activator of choice between layers of greens and browns. If you’re trying to boost an existing pile, mix the activator in while turning the compost.
    • Remember, while activators can speed up the process, maintaining the right moisture level, aeration, and the green-to-brown ratio remains crucial.
  • Potential Concerns:
    • Over-reliance on commercial activators can be costly and, in some cases, unnecessary. Nature often provides the required materials for free.
    • Some activators, especially manure, should be used judiciously to avoid an overly nitrogen-rich pile which can lead to ammonia smells.

In summary, compost activators, whether natural or commercial, can be valuable tools for both novice and seasoned composters. By understanding their role and using them effectively, you can optimize your composting process, ensuring a faster and smoother transition from waste to nutrient-rich humus.

Keeping Pests Away

Unwanted pests can not only disrupt your composting process but also contribute to bad smells. Ensure that your compost bin or pile is covered and avoid adding meat, dairy, or oily foods which attract these pests.

Troubleshooting and Fixes

Every gardener, at some point, faces challenges with their compost pile. Whether it’s an unexpected odor, a pile that refuses to decompose, or a surprise visit from unwanted pests, knowing how to troubleshoot and rectify these issues is essential. Here’s a detailed guide to help you navigate through some common composting pitfalls:

  • Problem: Foul Odor
    • Potential Causes: Lack of oxygen leading to anaerobic conditions, too many greens, excessive moisture, or the presence of meat and dairy.
    • Solutions: Turn the pile to reintroduce oxygen, add browns to balance out the greens, ensure proper drainage, and avoid adding materials like meat and dairy that attract pests and produce strong odors.
  • Problem: Compost is Too Dry
    • Potential Causes: Insufficient greens, excessive browns, or hot and arid conditions.
    • Solutions: Add fresh green materials, sprinkle water while turning the pile, or cover the compost with a tarp or lid to retain moisture.
  • Problem: Compost is Too Wet
    • Potential Causes: Overabundance of greens, poor drainage, or excessive rainfall.
    • Solutions: Incorporate more browns, turn the pile frequently to allow evaporation, and consider relocating the compost bin to a raised or better-draining location.
  • Problem: Pile Isn’t Heating Up
    • Potential Causes: Insufficient size, lack of nitrogen-rich materials, or poor aeration.
    • Solutions: Ensure your compost pile has a sufficient volume (at least 3×3 feet), add greens or compost activators, and turn the pile to introduce more oxygen.
  • Problem: Attraction of Pests (rats, raccoons, flies)
    • Potential Causes: Presence of meat, dairy, or oily foods; easily accessible compost pile.
    • Solutions: Avoid adding materials that attract pests, turn the compost regularly, and consider using a compost bin with a secure lid or mesh wiring to deter larger pests.
  • Problem: Presence of Undecomposed Chunks
    • Potential Causes: Large pieces of waste, woody materials, or low microbial activity.
    • Solutions: Break down or shred materials before adding them to the compost, turn the pile to reintegrate larger chunks, or add compost activators to boost microbial action.
  • Problem: Mold or Fungal Growth
    • Potential Causes: Overly wet conditions, lack of aeration, or introduction of moldy materials.
    • Solutions: Ensure proper drainage, turn the pile frequently, and avoid adding already moldy materials to the compost.

Remember, composting is both an art and a science. While it’s guided by scientific principles, local conditions, the specific materials you have, and even the season can influence outcomes. Regular observation and adjustment, armed with the knowledge of potential issues and their fixes, can ensure you maintain a healthy, productive compost pile.


The art of composting is a dynamic interplay between nature’s processes and human intervention. By transforming organic waste into rich, nourishing compost, we not only contribute to a sustainable environment but also cultivate a more fertile and productive garden. As we’ve journeyed through the essentials of composting, from understanding its components to troubleshooting common issues, it’s clear that while challenges may arise, they can be readily addressed with knowledge and patience.

Remember, every compost pile is unique, shaped by its environment, the materials introduced, and the care it receives. By maintaining the right balance of greens and browns, ensuring adequate aeration, and moisture, and occasionally giving it the boost of an activator, even the most stubborn compost challenges can be overcome.

As you continue your composting endeavors, take pride in the fact that you’re not just disposing of waste, but actively participating in a cycle that rejuvenates the earth. Each time you sprinkle that dark, crumbly, earth-scented compost onto your garden, you’re cementing your role as a steward of the environment, turning waste into wonder and fostering a greener, more vibrant world.

In the end, composting is more than just a gardening technique; it’s a testament to nature’s incredible ability to regenerate and our role in facilitating that magic. Happy composting!

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