14 Benefits of Composting

guy in plaid shirt holds trowel of compost in one hand and potted pot in other

Treehugger / Sanja Kostic

Did you know that when applied to soils, compost helps retain water so well that it can help reduce the need for irrigation? That goes for big farms as well as your own home garden.

Composting has environmental, economic, and social benefits on scales large and small. Some are direct and immediate, and others happen over the longer term. Learn about the full spectrum of benefits composting has to the soil, ecosystems, municipalities, waterways, and home gardens.

Soil Benefits of Using Compost

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Treehugger / Sanja Kostic

The benefits of compost to soil quality are many, as you'll read below. The fact that compost can improve soil is especially important since soil quality is diminishing in the U.S. and in many agricultural areas where food is grown. One of the simplest and easiest ways to improve soils, whether that's in city parks, or your own veggie patch, is adding compost.

Compost Feeds the Soil Food Web

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Treehugger / Sanja Kostic

As compost breaks down, it delivers important nutrients into the soil. Compost contains the three primary nutrients plants need: nitrogen, phosphorous, and potassium. Not only does compost feed the plants that grow in this soil, but it does so using existing materials, many of which are free or byproducts of the food system already. Compost also increases the number and variety of beneficial bacteria and fungi in the soil, which helps plants grow.

Reduces the Need for Chemical Fertilizers

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Treehugger / Sanja Kostic

Chemical fertilizers have a host of environmental consequences, beyond providing nutrients to the soil where they are applied. First, they need to be manufactured, shipped, and applied, all of which take time and money—as well as carbon emissions, since many fertilizers are made from nonrenewable petroleum products. Getting those fossil fuels from the earth has a huge carbon footprint, and then it takes energy to make them into fertilizers, as well as move them to where they need to go.

Not only do the chemical fertilizers have these various costs, they have also been found to harm the waterways they flow into after they are used on crops. The excess nutrients run off into waterways, and regularly cause algae blooms, which eventually die and during their decomposition, oxygen is lost from the water. These "dead zones" then kill fish or force them to move. Compost can prevent these carbon emissions and not just go easier on waterways, but even actually improve them (see below).

Using compost can increase the soil's ability to retain water to such a significant degree that it can reduce the need for irrigation, which is especially important for farmers who live in areas that are drying out or experiencing more drought.

Of course, it depends on the compost—as well as soil conditions and ambient air temperature and moisture levels—precisely how much more water a soil mixed with compost can hold. However, studies have shown that, for every 1% of organic matter content, "soil can hold 16,500 gallons of plant-available water per acre of soil down to one foot deep," according to Michigan State University Extension. That doubles if you can get the organic matter to 2% (it's hard to get it too much higher than that since the organic matter breaks down).

Compost Increases Soil Moisture

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Treehugger / Sanja Kostic

Other studies have shown that compost reduces crust forming on soil (so water can get into the soil more easily), and helps disperse water laterally from where it hits the ground, which means it will evaporate less quickly. All of these things help water get to plant roots more effectively.

It Prevents Soil Erosion

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Treehugger / Sanja Kostic

From highway embankments in Louisiana, to sloped and tilled fields in Illinois, the addition of compost to soils has been found to reduce soil erosion, preventing runoff of soils, which protects streams and other waterways from turbidity (muddy waters) that can harm fish and aquatic invertebrates. This happens because composted soils are better able to retain water.

Compost Benefits to Plants

Not surprisingly, when soil health and water availability are improved by compost, the plants that grow in that soil also reap the benefits.

It Aids Plant Growth

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Treehugger / Sanja Kostic

Plants that grow in soils amended with compost produce significantly more biomass. That means 50% or more grass in grasslands that cattle graze on, or more veggies. In an Italian study, compost increased lettuce and kohlrabi growth by 24% and 32% respectively.

Composting Improves Plant Nutrition

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Treehugger / Sanja Kostic

The quality of produce grown in compost tends to be higher as well. Quinoa plants in India improved antioxidant defense machinery leading to a significant increase in the ability of the plants to take nutrients from the soil. In a long-term study in China, wheat fields had significantly increased yields versus a control field of uncomposted soil.

It Can Reduce Plant Mortality Rates

Not only do more plants grow in soils that have been composted, but they also grow stronger, reducing the diseases plants can get. Since crop failure is a cost for home gardeners as well as farmers, this makes compost another way to save money when growing food or other plants.

Environmental Benefits of Composting

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Treehugger / Sanja Kostic

Of course, improving the soil and growing plants with fewer chemicals are both environmental benefits, but there are more direct ways composting can help the larger environment by reducing greenhouse gases and waste.

This is an obvious one—after all, if food waste and garden scraps don't go to the landfill, that will reduce how much space (and fees) a town pays for garbage disposal. But what is surprising is how much waste can be diverted with composting, and how significant the savings are.

Composting Reduces Waste

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Treehugger / Sanja Kostic

According to the EPA, food scraps and yard waste comprise more than 30% of a typical waste stream. Yes, that's almost 1/3 of our garbage, that could not only be kept from the landfill, saving space and saving townships and cities money—but can be turned into beneficial material that can replace or reduce costly chemical fertilizers used by municipalities, or give free nutrition to home gardens.

It Saves Money

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Landfilling garbage is expensive, and prices only keep rising because landfill space keeps shrinking. In 1990 there were more than 6,000 landfills in the United States; that number has dropped to 1,269 in 2018.

In 2020, the average cost to landfill a ton of solid waste was almost $54 per ton (In California, Oregon, and Washington, that price was significantly higher, at $70 or more per ton). If the U.S. sends more than 250 million tons of waste to landfills every year, those costs add up—now imagine slashing them by 1/3. That's potentially billions of dollars saved by composting.

Composting Reduces Methane Emissions at Landfills

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Treehugger / Sanja Kostic

When organic material breaks down in an oxygen-poor environment, like a landfill (garbage stacking up doesn't let enough air into lower layers), it goes through anaerobic decomposition. That creates methane, a greenhouse gas that's 28-34 times stronger than the same amount of carbon dioxide. And landfills create a lot of methane (they are the third-largest source of the gas in the U.S.): By volume, the gas that comes from a landfill is 45% to 60% methane and 40% to 60% carbon dioxide.

A way to reduce the amount of methane landfills produce is to compost those materials (like organic matter) that create methane when they anaerobically decompose

It Can Sequester More Carbon From the Air

woman holds stainless steel bowl of compost dirt with one hand and sprinkles dirt with other

Treehugger / Sanja Kostic

A 2018 report found that just a 1/4 inch of compost added to several different types of soil in California "resulted in a detectable and significant net increase in soil carbon storage" relative to untreated soils. About 900 extra pounds of carbon per year per acre were sequestered in soils with compost added.

Interestingly, when modeled over time, this effect lasted 30 years, with the greatest sequestration potential about 15 years after just the one application of compost.

The scientist behind the report, Dr. Whendee Silver, calculated that spreading 1/2 inch of compost over half of California's grasslands could remove carbon from the air at such a significant rate that it would balance the greenhouse gas emissions for the entire state of California for a year.

Composting Makes Use of Agricultural Waste

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Treehugger / Sanja Kostic

When most crops are grown and processed, there is often waste in the form of extra plant materials that aren't needed. A study in India found that while about half of this waste was used by local people as roofing material, for animal feed, fuel for heating, or packing materials, the rest of it would be disposed of by burning it, which is a cheap and easy way to get rid of the extra material and ready a field for the next planting.

However, burning leads to air pollution and negative respiratory health effects, and it also contributes little to the soil that has been depleted in growing the crops. Using this material as a compost both prevents the negative impacts of the burning and makes use of a free source of nutrients back into the soil.

Composting Can Help With Storm Water Management and Quality

As we learned in the soils section above, compost keeps more moisture in soils, leading to less runoff. Compost can be used instead of other materials like plastic sheeting in places with disturbed soils, like construction sites, according to the EPA.

Composting Also Has Social Benefits

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Treehugger / Sanja Kostic

Whether home composting in your backyard or adding to your city's weekly pickup, once you start composting you begin to realize the amount of food that is wasted and its cost. In some cases, this awareness may help households reduce food waste in general.

Also, when this former garbage is collected separately, its value is highlighted and the idea of compost as "black gold" gains new significance. Kids can also learn valuable concepts in environmental science, agriculture, chemistry, and the carbon cycle by learning about composting and engaging in it themselves. It's simple enough for even young kids to understand, and the complexity can ramp up as kids grow.

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