Compost facts for kids

Community composting in rural Germany

Compost is a special mix of natural ingredients. People use it to help plants grow strong and healthy. It also makes soil better for planting. You can make compost by letting plant scraps, food waste, and other natural materials break down. This process is called decomposition.

The finished compost is full of good things for plants. It has many nutrients and helpful tiny living things. These include bacteria, worms, and fungi. Compost makes soil more fertile in gardens and farms. It helps reduce the need for chemical fertilizers.

Compost gives food to crops. It also makes the soil richer. It adds a substance called humus. Plus, it brings in good microbes. These microbes can fight off plant diseases in the soil.

Making compost starts with mixing "green waste" and "brown waste." Green waste has lots of nitrogen. Examples are leaves, grass clippings, and food scraps. Brown waste has lots of carbon. This includes wood chips, paper, and dry stalks.

These materials slowly break down over several months. This turns them into humus. Composting can be a simple or a very careful process. You can add water and air, and turn the mix regularly. This helps the materials decompose faster.

Tiny Fungi, earthworms, and other small creatures help break down the organic stuff. Special Aerobic bacteria and fungi do the chemical work. They turn the waste into heat, carbon dioxide, and plant food.

A composter made from a hollow log

Composting is important for managing our trash. Food and other compostable items make up about 20% of what goes into landfills. In landfills, these materials break down very slowly without air. This creates harmful gases.

Composting is a much better choice for the environment. It helps reduce harmful methane emissions. Methane is a powerful greenhouse gas. Compost also has many other benefits. For example, it can help restore damaged land. It can also be used to build wetlands.

How Does Composting Work?

A home compost barrel

Compost bins at a college organic farm

Different materials in a compost pile

A heap of food scraps for composting

Composting is a natural way to break down organic waste. It uses air, which is called an aerobic process. This method helps us recycle natural materials. It turns them into a rich, soil-like substance called compost. This compost is great for feeding plants.

What Do Composting Organisms Need?

For composting to work well, tiny organisms need four main things:

• Carbon: This gives them energy. When microbes use carbon, they create heat. This heat is important for the composting process. Materials high in carbon are usually brown and dry.
• Nitrogen: This helps the organisms grow and make more of themselves. They need nitrogen to break down carbon. Materials rich in nitrogen are often green and wet. This includes colorful fruits and vegetables.
• Oxygen: Air is vital for the organisms to break down carbon. Special bacteria need at least 5% oxygen to do their job.
• Water: The right amount of water keeps the organisms active. Too much water can stop air from getting in, which is not good for composting.

When these ingredients are in the right balance, microorganisms work fast. They make the compost pile warm. You need to turn the compost pile sometimes. This adds oxygen and keeps the moisture level right. A good balance of air and water helps keep the pile hot. This continues until the materials are fully broken down.

Carbon and Nitrogen Balance

Composting works best with a specific mix of carbon and nitrogen. This is called the carbon-to-nitrogen ratio. A good ratio is about 25 parts carbon to 1 part nitrogen. If there's too much carbon, the process slows down. If there's too much nitrogen, some of it might escape as gas.

Almost all plant and animal materials have both carbon and nitrogen. For example, fresh grass clippings have more nitrogen. Dry autumn leaves have more carbon. Composting is an ongoing process. You can keep adding new materials and managing the pile.

Who Are the Composting Organisms?

Many different organisms help break down organic matter. They need the right mix of water, oxygen, carbon, and nitrogen. These helpers fall into two groups: chemical decomposers and physical decomposers.

Chemical Decomposers

These tiny helpers perform chemical changes on the waste.

• Bacteria: These are the most important and common microorganisms in compost. They process carbon and nitrogen. Then they release nutrients that plants can use. These nutrients include nitrogen, phosphorus, and magnesium.
  • Mesophilic bacteria start the composting process. They break down organic material and raise the temperature. They also help "cure" the compost, making it ready for plants.
  • Thermophilic bacteria love high temperatures. They become active once the pile gets warm. They thrive between 40 and 60 degrees Celsius (104-140°F). These bacteria help kill harmful germs in large compost piles.
  • Actinomycetota: These special bacteria break down tough materials. This includes paper, bark, and woody parts of plants. They give compost its pleasant, earthy smell. They also make carbon, ammonia, and nitrogen available to plants.
• Fungi: Molds and yeasts are types of fungi. They help break down materials that bacteria can't. This is especially true for the tough woody parts of plants.
• Protozoa: These tiny creatures help break down organic matter. They also eat inactive bacteria and fungi.

Physical Decomposers

These organisms break down waste into smaller pieces by chewing, tearing, or digesting it.

• Ants: They build nests, which makes the soil airy. They also move nutrients around the compost.
• Beetles: Some beetle larvae, called grubs, eat decaying vegetables.
• Earthworms: They eat partly composted material. Then they excrete "worm castings." These castings are rich in nitrogen, calcium, phosphorus, and magnesium. Worm tunnels also help air and water move through the compost.
• Flies: Flies eat almost all organic material. They also introduce bacteria into the compost. Mites and high temperatures usually keep their numbers in check.
• Millipedes: They help break down plant material.
• Rotifers: These tiny animals feed on small plant particles.
• Snails and slugs: They eat fresh plant material. It's a good idea to remove them from compost before using it in your garden. This prevents them from damaging your plants.
• Sow bugs: They feed on rotting wood and decaying plants.
• Springtails: These tiny insects eat fungi, molds, and decomposing plants.

What Are the Phases of Composting?

A three-year-old household compost pile

Composting usually goes through three main stages:

• Mesophilic phase: This is the first stage. Decomposition happens at moderate temperatures. Mesophilic microorganisms do most of the work. This phase lasts about 2 to 8 days.
• Thermophilic phase: As the temperature rises, this second phase begins. Special thermophilic bacteria take over. They break down materials at higher temperatures, usually between 50 and 60 degrees Celsius (122-140°F).
• Cooling and Maturation phase: As the easy-to-break-down materials run out, the temperature drops. The compost then enters a cooling and maturation stage. It becomes stable and ready to use.

Sometimes, if the compost pile is small, it might not get hot enough. This is called semicomposting. Only mesophilic microorganisms work in this process. It still breaks down organic matter, but it takes longer.

Hot vs. Cold Composting: Which is Faster?

How long composting takes depends on several things. These include the amount of material, how small the pieces are, and how often you mix it. Larger piles usually get hotter and stay hot longer. This is called hot composting. It's often used in big composting facilities. Hot composting can make finished compost in just a few weeks.

The Berkeley method is an example of fast composting. It can make compost in about 18 days. This method needs a large pile from the start. It also requires turning the pile every two days after an initial four-day period. This method uses smaller pieces of material and carefully controls the carbon-to-nitrogen ratio and moisture.

Cold composting is a slower process. It can take up to a year. This happens with smaller piles, like many home compost bins. These piles don't usually get very hot. You don't need to turn cold compost as often. However, parts of the pile might become too wet or packed down. This can stop air from getting in.

Keeping Compost Safe: Pathogen Removal

Composting can destroy some harmful germs (pathogens) and weed seeds. This happens when the compost reaches temperatures above 50 degrees Celsius (122°F).

Compost that has reached these high temperatures is very safe to handle. The heat kills most pathogens. The temperature needed to kill a pathogen depends on the type of germ. It also depends on how long the heat lasts and the pH level.

Compost products, like compost tea, can also help plants. They can stop diseases caused by certain plant pathogens. The good microbes in compost help fight off these harmful fungi. Sterilizing compost reduces its ability to fight diseases.

Important Safety Tips for Composting

When you turn compost that hasn't reached high temperatures, it's important to be safe. Always wear a mouth mask and gloves. This protects you from tiny germs that might be present. These germs can cause illnesses. For example, some fungi can grow in compost. High temperatures (over 50°C or 122°F) usually kill these harmful germs.

Why is Composting Good for Our Planet?

Compost helps the environment in many ways. It adds natural material to the soil. This makes the soil richer in nutrients. It also increases the number of helpful microbes in the soil.

Composting at home reduces the amount of yard and food waste. This waste would otherwise go to landfills or large composting centers. Fewer trucks are needed to pick up waste. This means less pollution from vehicle emissions.

What Materials Can You Compost?

You can compost many different types of waste. These come from homes, farms, and businesses. You can compost food scraps and yard waste at home. Or, these materials can be collected for large composting facilities. Some neighborhoods also have local composting projects.

Organic Solid Waste

A large compost pile steaming from heat made by tiny organisms.

Organic solid waste falls into two main groups: green and brown. Green waste is a source of nitrogen. This includes food scraps, grass clippings, garden trimmings, and fresh leaves. Animal carcasses and butcher waste can also be composted. These are also good sources of nitrogen.

Brown waste is a source of carbon. Common examples are dried leaves, straw, woodchips, and pine needles. Sawdust and wood ash (but not charcoal ash) also work. Paper and plain cardboard from wood are also carbon sources.

Animal Manure and Bedding

On many farms, animal manure is a key composting ingredient. It provides nitrogen. Bedding materials, like straw and sawdust, provide carbon. Farmers also use newspaper or chopped cardboard as bedding. The amount of manure composted depends on cleaning schedules and weather.

Different types of manure have different qualities. Cattle and horse manures mix well with bedding for composting. Pig manure is very wet. It needs to be mixed with straw or similar dry materials. Chicken manure needs to be mixed with materials high in carbon and low in nitrogen.

Recycling Human Waste Safely

Human excreta, sometimes called "humanure" in composting, can be added to compost. It is rich in nutrients. Solid human waste contains nitrogen, which helps plants make important amino acids. Liquid human waste (urine) has phosphorus. Phosphorus helps plants turn sunlight into energy.

Unlike feces, urine does not attract disease-spreading flies. It also does not contain the toughest pathogens, like parasitic worm eggs.

Animal Remains

Composting animal carcasses is a way to dispose of them. This material is rich in nitrogen.

Composting Methods and Technologies

A backyard composter

Large-Scale Composting

In-Vessel Composting

This method uses large containers or buildings. Organic waste is placed inside. The conditions like temperature and moisture are carefully controlled. This helps the waste break down quickly and efficiently. It's often used for large amounts of waste.

Aerated Static-Pile Composting

In this method, organic waste is piled up. Air is then blown through the pile using pipes or fans. This provides oxygen to the microorganisms. It helps the compost break down without needing to be turned.

Windrow Composting

This method involves making long piles of organic waste, called windrows. These piles are turned regularly. Special machines mix and aerate the compost. This helps speed up the decomposition process. It's common for large farms and municipal facilities.

Home and Garden Composting

Hügelkultur (Raised Garden Beds)

An almost completed hügelkultur bed, before soil is added.

Hügelkultur is a German word for "hill culture." It means making raised garden beds or mounds. These beds are filled with rotting wood. Then they are covered with soil.

Hügelkultur beds help hold water and warm the soil. The buried wood acts like a sponge. It soaks up water and stores it for plants. As the wood breaks down, it also releases nutrients.

Composting Toilets

Composting toilets are special toilets that don't use water. Instead, they collect human waste in a chamber. This waste then breaks down into compost. They are a way to recycle nutrients from human waste. These systems need careful management to be safe and hygienic.

Other Cool Composting Ideas

• Vermicompost: This is compost made by earthworms. The worms eat organic matter and produce "worm castings." These castings are very rich in nutrients. They are great for plants.
• Black Soldier Fly Larvae: The larvae of the black soldier fly can eat large amounts of organic waste very fast. They can even help treat human waste. The resulting material can still be used for nutrients.
• Bokashi: This is a fermentation process, not decomposition. It uses special microbes to ferment food waste. This includes items that are usually hard to compost. Bokashi keeps the nutrients and carbon in the waste. It quickly turns into food for soil microbes.
• Anaerobic Digestion: This process breaks down organic waste without air. It produces biogas, which is a fuel. This method helps reduce methane from landfills. Methane is a powerful greenhouse gas.

How Do We Use Compost?

Agriculture and Gardening

Compost used as fertilizer

Farmers spread compost over fields to grow crops like wheat and corn. They use special trucks or tractors to spread a thin layer. This compost is then mixed into the soil before planting. It helps rebuild poor soils and stop erosion.

In gardens, compost can be mixed with soil, coir, or peat. It makes the soil better and adds nutrients. It creates a rich growing mix that holds moisture. Compost is rarely used alone. It's often blended with other things like sand, bark chips, or clay. This creates a perfect loam for plants.

It's usually not recommended to plant seeds directly into pure compost. Immature compost might have substances that stop seeds from growing. It's common to use a mix of 20–30% compost for planting young seedlings. Compost can also help plants fight off diseases and pests.

Compost Tea

Compost tea is a liquid made by soaking compost in water. It's like a nutrient-rich drink for plants. You can make it by adding compost to water and stirring it.

Some people add air to the mix, while others don't. Aerated compost tea brews faster and has more microbes. Compost teas can help plants grow better. They also help fight plant diseases. However, adding extra nutrients to compost tea can sometimes cause harmful bacteria to grow.

Compost Extract

Compost extracts are similar to compost tea. They are liquids made by dissolving compost contents in a solvent. They are not fermented or brewed.

Buying Compost

You can buy compost in bags at garden stores. These often contain composted manure and peat. They might also have soil, fertilizers, and sand. There are many types of compost for different plants. You can find compost for vegetables, orchids, or seedlings.

Other Uses for Compost

Compost can also be used to restore damaged land and streams. It helps build wetlands. It can even be used as a cover for landfills.

The heat from compost can also be used. For example, it can help warm greenhouses. You can place compost piles around the outside edges of a greenhouse.

Rules and Guidelines for Compost

A kitchen compost bin for collecting compostable items

Many countries have rules for composting. These rules help make sure compost is safe and good quality. They started in Europe in the 1980s. More recently, the UK and US have also developed guidelines. These rules help protect people and the environment.

In the United States, some compost makers follow a testing program. This program helps ensure compost meets certain standards. It checks for things like nutrients, salt content, and pH.

Some cities and regions require people to sort their food and yard waste. This waste is then collected for composting. For example, cities like Seattle and San Francisco have these rules.

There are ongoing discussions about certain chemicals in compost. These chemicals can sometimes be found in compost made from treated sewage sludge. Experts are studying these chemicals to understand any health risks. Groups like the Sierra Club suggest home gardeners avoid using compost made from sewage sludge. This is a precaution until more is known about these chemicals.

A Look Back: History of Composting

A traditional compost basket

Composting has been around for a very long time. People in the early Roman Empire used it. Cato the Elder wrote about it in 160 BCE. Traditionally, people would pile up organic materials. They would let them decay until the next planting season. This was a common practice in traditional farming worldwide.

Composting became more modern in the 1920s in Europe. It became a key tool for organic farming. The first industrial composting plant opened in Wels, Austria, in 1921. Early supporters of composting included Rudolf Steiner and Sir Albert Howard. They helped spread the idea of sustainable farming. In America, J. I. Rodale helped bring modern scientific composting to the organic farming movement.

See also

In Spanish: Compost para niños