Composting: What It Is and How It Saves the Planet

Imagine you’ve just finished eating a banana. Where does the peel go? If your answer is “in the regular trash,” you’re unknowingly contributing to one of the most underestimated environmental problems of our time. Organic waste dumped in landfills decomposes without oxygen, releasing methane — a greenhouse gas dozens of times more potent than carbon dioxide. At the same time, that banana peel carries valuable nutrients that could return to the soil and feed new plants.

Composting is the elegant and ancient solution to this wasted cycle. In essence, it transforms organic waste into nutrient-rich fertilizer through controlled natural decomposition. It’s not new: ancient civilizations were already returning leftovers to the soil long before any climate crisis was on the agenda. What has changed is the urgency and scale of the problem — and the fact that today anyone, whether living in an apartment or a house with a yard, can practice composting.

In this article, you’ll understand what composting is, why it truly matters for the planet, how it works in practice, and how to start today without spending much or needing a large space.

What is composting and how does it work

Composting is a biological process in which microorganisms — bacteria, fungi, and other decomposers — break down organic matter (food scraps, dried leaves, untreated paper, coffee grounds) and transform it into compost, a dark material rich in organic matter and nutrients, similar to fertile soil.

For the process to work well, it needs four basic elements:

• Carbon (“brown” materials): dried leaves, cardboard, sawdust, straw
• Nitrogen (“green” materials): fruit and vegetable scraps, coffee grounds, eggshells, grass clippings
• Moisture: the compost should be as moist as a lightly squeezed sponge
• Oxygen: regular turning ensures aeration and speeds up decomposition

Researchers generally point to an ideal proportion of carbon to nitrogen of around 25 to 30 parts of carbon to 1 part nitrogen, but in home practice, you don’t need to measure: alternating layers of brown and green materials works very well.

Types of composting: which one to choose

There are different methods, each suited to a different living situation:

The worm bin is especially popular in cities because it doesn’t produce bad odors when well-managed, takes up very little space, and produces excellent quality compost thanks to the work of red California earthworms (Eisenia fetida).

Why composting saves the planet: the numbers that matter

The impact of organic waste on climate is often underestimated. According to data from the United Nations Food and Agriculture Organization (FAO), about one-third of all food produced in the world is lost or wasted — and much of that material ends up in landfills.

When organic matter decomposes in anaerobic conditions (without oxygen), as happens when buried in landfills, it releases methane (CH₄). The IPCC (Intergovernmental Panel on Climate Change) classifies methane as a gas with global warming potential far superior to CO₂ over 20-year timeframes — making organic waste management an urgent climate issue.

In Brazil, the situation is significant. The country generates tens of millions of tons of solid waste per year, and the organic fraction has historically represented more than half of that volume, according to data from the Brazilian Association of Public Cleaning and Special Waste Companies (Abrelpe). Most of it still goes to landfills or dumps — and the National Solid Waste Policy (Law 12,305/2010) specifically provides for the reduction of this practice, with composting as a central alternative.

Direct benefits for soil and biodiversity

Beyond reducing emissions, compost actively improves soil:

• Increases water retention, crucial during dry periods
• Improves soil structure, making it more aerated and fertile
• Stimulates microbial activity, which is the foundation of healthy soils
• Reduces the need for synthetic fertilizers, whose production is energy-intensive and emits greenhouse gases

Soils rich in organic matter also sequester carbon — meaning composting helps both avoid emissions and capture carbon already in the atmosphere.

What can and cannot go into a compost bin

One of the biggest fears for beginners is making a mistake and creating a bad odor or pest problem. The good news is that the list of what can go in is much longer than what cannot.

Can compost:

• Fruit and vegetable peels and scraps
• Coffee grounds and paper filters
• Tea bags (without metal staple)
• Eggshells (rich in calcium)
• Dried leaves and thin twigs
• Cardboard and untreated paper, torn into small pieces
• Grass clippings and plants without seeds
• Bread and cereal scraps (in worm bins, in moderation)

Should not compost:

• Meat, fish and dairy (in conventional composters — bokashi accepts them)
• Oils and excessive fats
• Diseased plants or those with pests
• Feces from carnivorous animals
• Materials treated with excessive pesticides
• Glossy, laminated or brightly colored ink paper

How to make a home composter: step by step

You don’t need expensive equipment to get started. A simple home composter can be made with buckets or purchased at reasonable prices from garden shops.

To set up a basic worm bin:

1. Choose two or three plastic buckets or boxes with lids (clean paint buckets work fine, for example). Make small holes in the base of each for drainage and ventilation.
2. Prepare the worm bedding: place a layer of dried leaves, moist cardboard, or soil in the bottom of the first container.
3. Get red California earthworms — found in fishing shops, garden stores, or community composting groups. Start with a few hundred.
4. Add organic waste in thin layers, always covering with dry material (leaf, cardboard) to prevent odor.
5. Keep in a cool, shaded place, away from direct sunlight. Worms prefer temperatures between 15°C and 25°C.
6. Water lightly if too dry and add more brown material if too wet or smelly.
7. After a few weeks, finished compost (humus) will be at the base — dark, with the smell of moist earth. This material can be used directly on plants and gardens.

The complete process takes 2 to 4 months depending on the amount of waste, temperature, and management.

Composting in an apartment: yes, it’s possible

Living in an apartment is no excuse not to compost. Besides the worm bin (which fits under the sink), the bokashi method is an excellent urban option: it uses bran fermented with efficient microorganisms (EM) to “ferment” waste, including meat and dairy, without odor and in minimal space.

Another alternative is to participate in community composting networks, which exist in several Brazilian cities. Many condominiums, farmers markets, parks, and city halls offer organic waste collection points. It’s worth researching what exists in your neighborhood — often the solution is already nearby.

If you want to adopt other habits that reduce your daily environmental impact without complicating things, also check out this article about seasonal foods: why buy and how to save. Buying seasonal foods reduces waste in the production chain — and leftover seasonal fruits and vegetables are great candidates for your compost bin.

How to use finished compost

After all the work, you’ll have one of the best natural inputs for plants. Mature compost — that with a dark, granular appearance and earthy smell — can be used in several ways:

• Mixed into substrate for pots and gardens (20 to 30% of total volume)
• As mulch around plants in the garden, helping retain moisture
• Diluted in water to make “compost tea” and water more sensitive plants
• Donated or traded with neighbors, urban garden projects, or schools

If you live in an apartment and don’t have plants, the compost can be taken to collection points, farmers markets, or offered in urban gardening groups — there’s never a shortage of destinations for good compost.

Conclusion: a small action with real impact

Composting is one of the most concrete gestures a person can make for the environment. It closes the organic matter cycle, reduces greenhouse gas emissions, improves soil, and decreases the amount of waste going to landfills. And contrary to what it seems, it doesn’t require much space, time, or money.

Starting with a small worm bin or participating in a community composter already makes a difference — and it often marks the beginning of a larger shift in perspective about what we throw away. To deepen this sustainable habits journey, also see how to preserve forests with attitudes that make a real difference in your daily life.

The planet doesn’t need perfection. It needs people willing to act, even on a small scale. And that banana peel in your hand now? It deserves a better destination than the landfill.