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What Can and Can’t Go in a Compost

Composting is one of the sustainable soil management techniques advocated for in the global efforts for the conservation of healthy soils. With plenty of organic waste from households, institutions, and industrial firms ending up in landfills and incinerators, we have more waste for composting than we could exhaust. But not every type of waste is suitable for compost.

So, what can and can’t go in a compost? Any organic waste that can compost to form humus and which is free of toxins is good for compost. Non-compostable waste is toxic and should not be dumped in compost as this compromises the entire composting process.

If you are planning to create compost at home, choosing what should or shouldn’t go in the compost can be a tricky decision. This article saves your day by listing the types of organic waste that can be composted and those that can’t. It also tells you about the methods and process of successfully composting waste to humus and the benefits that come with it.

Read on to understand the details of each of these aspects. We’ll start you off with a comprehensive understanding of composting as a mode of soil conservation.

What Types of Waste Products Can and Can’t Go in a Compost

Deciding on what waste products can or can’t go in a compost is determined by two key factors:

  • The ability of the waste product to compost and be transformed into humus.
  • The absence of toxins that can alter the required environmental conditions for the composting process.

In this light, we will group waste products for compost into three categories:

  1. Waste products that readily decompose (quickly or slowly) and can go into compost without causing any problems.
  2. Waste products that can decompose but need some extra preparation before going in a compost.
  3. Waste products that are an absolute ‘no’ for the compost.

Waste products that can go in a compost

Waste products that are considered suitable for compost are organic waste that compost readily without any complications.

Compostable material may take different rhythms to compost. In this light, we can think of materials that compost fast and those that compost slowly.

Materials that compost fast include:

  • Fruit and vegetable waste (lettuce, banana and potato peels, avocado skin, etc)
  • Cooked carbohydrates such as pasta and rice
  • Bean curd (tofu)
  • Algae (seaweed)
  • Non-dairy spoilt products like coconut or almond milk
  • Coffee grounds and loose-leaf tea: they are considered green compost material and are a good source of nitrogen. They can simply be thrown into the compost pile.
  • Vegetarian animal manure (from cows, goats, sheep, horses, hamsters, rabbits, etc)

Materials that compost slowly include:

  • Herbs and spices
  • Fluffs, hair, and fur
  • Stale seeds (should be chopped to prevent sprouting)
  • Preserved plant products like jams and marmalades
  • Nutshells (not walnut shells)
  • Wine corks (should be chopped)
  • Avocado, mango, peach, and plum seeds
  • Shredded newspapers
  • Plant leaves and flowers: they require occasional turning and consistent moisture to create the required carbon for the composting process.
  • Pure cotton byproducts
  • Biodegradable diapers
  • Grass and plant clippings: they should be organic, not grown with synthetic fertilizers and be chopped into small pieces. Leaving them whole in the compost pile slows down the process and can cause bad odor.  They should also be turned periodically to facilitate airing.
  • Sawdust, wood chips, and cardboard: wood chips and cardboards are great for aeration but should be turned regularly; even every week.
  • Corn/maize cobs

Waste products that can go in a compost with prior preparation

Certain waste products should be assessed for their appropriateness in the composting process. This means that the waste material may compromise the process if used in a certain form but can also be considered as material for compost if prior preparation or assessment is done.

Here are some of the waste products that can go in a compost with prior preparation or assessment.

  • Manure from non-herbivores: manure from herbivores is usually good for compost but not so waste from meat-eating animals. Humans, dogs, pigs, and cats are all carnivores and their waste may be prone to disease-bearing pathogens.

One condition for using this type of wastes is that the compost is going to heat at high temperatures which are capable of eliminating the germs. If this does not happen, the wastes can render the entire compost useless. It’s therefore advisable to leave them out.

  • Food waste that attracts rodents and scavengers: waste foods that have small amounts of dairy, oil, and fat or those that naturally attract rodents and hunters such as eggshells, bread, and noodles may be a threat to the composting process.

If your compost pile is consistently being scavenged, the composting process is compromised. If instead you are using the bin method and your compost container is out of reach of scavengers, then these products may be considered. Note that some of them, like eggshells, belong to the slow-composting category.

Washing the products before adding them to the pit compost may be considered. But even then, you have no guarantee that you can cheat the strong-smelling power of these animals.

  • Invasive weeds: these are weed plants that are hard to die. While they may readily decompose, they are also known to resurrect and spread. The deal is that they can be part of the process because they will compost, but they pose the risk of spreading in your garden or farm. It is better to leave them out altogether. Examples of invasive weeds are the Canada thistle and the creeping Charlie.
  • Color newspapers and other printed material: even though a lot of the colored ink used on papers today is from soy products, some of the print paper may have a wax coating. This may be harmless but might instead compromise the composting process of the paper. To be able to use such paper in a compost and hasten its composting, shred the paper into small sizes. Nevertheless, leaving waxed paper out of the compost may be a safer option.

Waste products that can’t go in a compost

Waste products that are an absolute ‘no’ in composts are non-compostable or pose the threat of harmful bacteria and toxins for the compost. They include the following.

  • Weed seeds: they can easily sprout and spread through the compost and later in the garden or farm where the mature compost is used.
  • Diseased plants: plants that are infected or die of disease should be left out of a compost completely. The high temperatures in the compost do not kill these diseases and they will spread to other plants once used as humus.
  • Meats, fish, and bones: these have the risk of diseases and are an enticing attraction for scavengers. They are also extremely slow in decomposing and can overheat the compost. It is better to leave them out than risk the entire process of composting.
  • Non-organic food waste: it is grown with synthetic fertilizers and may be subjected to the use of pesticides and herbicides. All these are toxin compounds for the composting process.
  • Walnut and walnut shells: verified to be toxic to many plants.
  • Dairy and dairy products, grease, fats, and oils: apart from the fact that they are slow in composting and can compromise the aeration process, these waste products are an attraction for hunters and can ruin your composting process.
  • Citrus fruits and pickled foods: they are highly acidic and can destabilize the compost by killing the good bacteria needed for the breakdown of organic waste. It is advisable to leave such waste out of your compost.
  • Coal and charcoal: these contain iron and sulfur in quantities that are toxic to many plants.
  • Inorganic materials: these materials are non-compostable and will not break down. Besides, they can also be toxic for your compost. They include metals, glass, aluminum foil, and plastics.

The Methods and Process of Composting

Composting is easy and can be realized in tiny indoor space or the open outdoor. Whether you are a farmer or gardener, you can use one of the methods of composting to produce humus and enrich the physical properties of the soil in your farm or garden. You can also use mature compost (humus) to directly grow crops and plants.

Methods of composting

Depending on the extent and purpose of composting, one can choose from these types of composting.

Backyard/onsite composting

This type of composting entails the use of organic waste from households, institutions like schools and hospitals or commercial entities for composting. The compost is onsite and food and other organic wastes like dry leaves, grass and plant clippings can be naturally decomposed in a selected space.

Onsite compost can take up to two years to mature, but, the process can be accelerated through turning and the maturing period reduced to 2-6 months. Mature compost is used onsite to enrich the soil for crop or plant gardening.

Composting onsite is optimal for organizations where considerable amounts of food waste are disposed of daily. Little time and resources are needed even though education on the process of composting is important. Training ensures that the composting is done in a way that does not emit a bad odor or attract animals and insects.


This method of composting uses red worms to consume and breakdown organic waste and convert it to compost castings.

A suitable bin is used for the composting process which makes the method appropriate in contexts where people are interested in making compost but have little space for onsite or backyard composting. Such contexts include offices and condos. Schools and other institutions can also use this method for soil-conservation learning and demonstrative purposes.

Even though vermicomposting is easy to realize, worms require controlled levels of temperature. Extreme temperatures can kill the worms and compromise compost maturity. Temperatures ranging between 550 F and 770 F are recommended. If vermicomposting in done in hot climates, shades and cooler positions within a building should be identified for the compost bin.

Worm bedding or the provision of shredded organic material like newspapers and carbon-rich soil is vital in vermicomposting. This is because it provides a favorable habitat for the worms, even when the conditions are of the recommended levels.

With the correct worm and compost ratio (around 1000 worms for a pound of organic waste), vermicomposting will create mature castings in 3-4 months. The castings are optimal as potting soil.

Aerated/turned windrow composting

Aerated windrow composting is the ideal choice for community composting or institutions and businesses where large amounts of organic waste are produced daily. These could be restaurants, hospitals, and packing plants among others.

Windrows are the long piles into which organic waste is formed for composting. An ideal windrow measures around 16ft in width and 8ft in height. It can be as long as space allows, but should consider ease of turning.

Once formed, the windrows are occasionally turned to allow aeration. Turning could be manual or mechanical.

Where temperatures are high or the climate arid, windrows are sheltered to avoid unnecessary loss of moisture. Also, windrows can be raised in a form that allows the flow of excess water during the rainy seasons. The formation of windrows allows the conservation of adequate temperatures (around 1400F) at the core of the compost, even in cold climates.

Because aerated windrow composting is large-scale, the projects may be liable to legal control. This may mean seeking legal supervision and authorization for setting up composting sites as well as submitting mature compost samples to test for bacterial and toxin contamination before using the compost in farms and gardens. Check with your local agricultural authority before initiating a community or institutional composting project.

Even though aeration composting requires large amounts of organic waste and a lot of labor, its greatest advantage is that it produces large amounts of compost, implying the enrichment of large quantities of soil.

Aerated static pile composting

As the name suggested, aerated static pile composting entails heaping compostable waste in a single pile and leaving it to mature without turning. To facilitate aeration throughout the pile, bulking agents such as shredded papers and plant clippings are added to the compost pile.

Alternatively, the pile of organic matter is placed on top of a series of pipes to allow air movement from the bottom to the top of the compost heap. When done commercially, timed or temperature-sensitive air blowers can be used to deliver air to the compost heap.

As with windrow composting, compost piles may be covered to avoid loss of moisture in hot climates or seasons. Pile composting may be a challenge in cold seasons because no active turning is done. This means that aeration is compromised even though optimal temperatures may be maintained at the core of the heap. To counter this challenge, compost piles may be placed indoors where it is warmer.

Pile composting may also be prone to bad odor. To counter this challenge, a layer of mature compost may be placed over the compost heap to help maintain the desired levels of temperature throughout the pile. A biofilter made from mature compost can also be used to draw bad air from the compost pile.

The greatest advantage of static pile composts is that they can deliver mature compost within 3-6 months.

In-vessel composting

This method uses a drum or other suitable containers to create controlled environmental conditions for organic waste composting. It can be used for large-scale composting where mechanical methods are put in place to aerate the compost periodically.

The core advantage of in-vessel composting is that large amounts of compost can be made without using much space. This can be done indoors in commercial kitchens or other contexts where large amounts of organic waste are produced daily.

In-vessel composting does not pose challenges of bad odor or leaching. However, the process may be costly since technical know-how is required to set the right environmental conditions for composting and for timing periodic mechanical aeration.

A disadvantage of in-vessel composting is that after composting is completed in the vessel, the compost needs a few weeks or months in the open air to facilitate stabilization, microbial activity, and cooling.

With the ample knowledge of the methods of composting, we can now explore the process of composting.

The process of composting

The process composting begins with the preparation of the organic material for compost and ends with mature humus. The simple test for mature compost is a dark or dark-brown color that has a smell similar to that of soil.

To create mature compost, high temperatures are required to keep away weed germs and harmful microorganisms. Organic wastes are combined with other manures in the right ratios and piled in pits or composting containers. Bulky materials such as wood chips are added to hasten the breakdown of the organic material. Then, the compost is left to mature.

If you are planning to compost in your backyard or garden, follow these 5 steps to obtain the best results.

1. Identify your composting space

For home composting, space may refer to a bin if you are opting for vermicomposting or a shady spot if you are going for backyard composting.

Select a cool position for your bin with indoor composting and choose a dry spot near a water source in the backyard for pile composting.

2. Add composting material in the right ratios

Whatever method of composting you opt for, it is important to mix the material in the right ratios. The United States Environmental Protection Agency recommends mixing the following:

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  • Browns: including dry leaves and plant clippings
  • Greens: from freshly mowed grass, fruit and vegetable waste, or other kitchen wastes such as coffee grounds.
  • Moisture: the recommended amount of water.

The rule of thumb is to use browns and greens in equal amounts. Browns will give the required amount of carbon for your compost while the greens provide the necessary nitrogen. Moisture breaks down the compost material.

3. Chop the organic material into small sizes

Browns and greens should be chopped into appropriate sizes before being thrown into the compost. Large sizes will take longer to compost or fail to do so altogether.

Ensure that the different sizes of organic matter are alternated to facilitate aeration and add moisture to dry waste as you include it in the pit.

4. Cover the compost to keep it moist

This step is optional but advisable especially in dry seasons when your compost is likely to lose moisture consistently. Canvas cloth can be used. But a layer of previously matured compost is better because it will not compromise aeration.

5. Harvest your compost

When the required period for composting is passed and your compost has a dark or dark-brown color all-through, then you can harvest your compost and use it to condition and enrich the soil in your garden or farm.

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Depending on the amount and the composting method, compost-harvesting time may be in two months or two years.

While using the right methods and process of composting, it is important to make sure that your compost product is good for use by the time it is harvested. This means including the right organic products and leaving out those that may compromise the maturity and purity of the end product.

Benefits of Composting

The benefits of composting can be seen from two main perspectives: the economic and the environmental. These benefits justify the engagement of households, communities, and governments in composting projects.

Environmental benefits of composting

The core environmental benefit of composting is its role in mitigating the emission of greenhouse gases and recycling nutrients back to the soil to enrich it. This works for better crop and plant growth.

According to, 95% of compostable food waste in the US ends up in landfills. This makes a considerable contribution to the production of methane and emits a substantial amount of carbon to the atmosphere.

If food and other wastes are composted, carbon becomes a productive component in the composting process rather than a source of atmospheric intoxication.

Other environmental benefits of composting include:

  • Composting replaces synthetic fertilizers in the production of food and the growth of plants and this is a healthier option for the soil and humanity in general.
  • The use of compost in crop production ensures higher and healthy yields when compared to synthetic fertilizers.
  • Composting reverts some adverse effects of human activity on the environment through reforestation, habitat revitalization, soil restructuring, and wetland restoration.
  • Humus from composting improves water retention in the soil and redirects carbon to a productive process.
  • Composting prevents diseases and pests while prolonging soil life.
  • The use of compost balances soil pH which is vital in reducing plant stress.

Economic benefits of composting

Economic benefits of composting can be read from the perspective of the amount of money saved in the substitution of costly chemical fertilizers in agriculture and the generation better crop production and quality when compost is used.

Specifically, the following are some of the economic benefits of composting:

  • Compost replenishes the soil with lost nutrients in a cost-effective natural process.
  • Because it’s a natural product, compost saves us the cost of soil conservation when soil-depleting agricultural processes are used. It also saves us the costs of using mechanical techniques for water retention in the soil while at the same time mitigating the cost of soil-detoxifying processes.
  • Institutions and businesses that produce large amounts of organic waste daily save a lot in reduced landfill fees through composting.
  • In irrigation farms, composting saves on the amount of water used since it helps retain the water while preventing the retention of unnecessary moisture. The same is true for plant and crop gardening.

Composting as Conservation of Healthy Soil.

It is estimated that 95% of global food production is from the soil. This implies that healthy soils are an indispensable resource for human subsistence.

According to the Food and Agriculture Organization of the United Nations (FAO), healthy soil functions as a living system. This means that it maintains a broad range of organisms that control the spread of weeds, harmful insects, and plant diseases. Healthy soil also forms a healthy interdependence with plant roots and naturally recycles vital plant nutrients.

When soil is healthy, its basic structure is maintained and this has positive outcomes for soil conservation and food production. In the long run, healthy soil maintains its carbon content, thereby contributing to the global efforts of climate change.

It is easy to understand from this description of healthy soil why composting is a form of healthy soil conservation. Composting is nature’s way of turning organic waste into compost, a natural fertilizer. The process of composting decomposes the organic waste into compost under the right conditions, making it a natural byproduct for enriching soil. Crops can also be directly grown in the humus that results from composting.

When organic products are added to a compost, microorganisms (fungi and bacteria) break down the products into simpler components that form humus. This happens under certain conditions:

  • Using the right type of organic products (decomposable and non-toxic).
  • Combining green and brown organic matter in the right ratios.
  • Reducing compost material into decomposable sizes.
  • Maintaining controlled levels of oxygen, moisture, and temperature.
  • Turning the compost once in a while to facilitate oxygen distribution.

The United States Environmental Protection Agency (EPA) considers composting the fifth of the six tiers of the food recovery hierarchy. While the first four levels focus on proactive ways to save food, composting aims at the conservation of healthy soil by adding what cannot be redeemed of food products into compost. This preempts unused food products from ending up in landfills and incinerators by using it to produce more food.

Final Thoughts

Composting contributes to the global soil management efforts that are crucial for the success of food security initiatives.

Composting conserves soil naturally. Organic waste is broken down by bacteria and fungi to produce compost which is used to enrich the soil and ensure better growth for food crops and plants.

Different methods of composting can be used depending on the extent of the composting process and the resources available. Vermicomposting may be appropriate for those with little space while aerated windrow composting should be considered for commercial or community level composting.

Organic material that is compostable and is non-toxic should go to a compost. Some waste products may be part of the compost after assessment and preparation while those that are toxic or non-composting should be left out of the compost.

Composting has benefits related to the environment as well as others that are commercial because they save us some money.

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All in all, composting should be considered as a noble way of reducing food wastage and a natural way of enriching soil.