Can You Use Partially Decomposed Compost?

Composting is a process that can take anywhere from weeks to several months or even years to complete depending on the size and contents of your compost. It may be tempting to just dig in and use the partially decomposed compost when you’re starting. 

You can’t use partially decomposed compost. The microbes in this compost breaking down the organic matter might feed on soil nutrients as they complete the decomposition process. Partially decomposed compost also has pathogens, organic acids, and ammonia compounds that could affect the health of your plants. 

In this article, I’ll explore the different stages of decomposition that compost goes through so you’ll know what is happening in your compost pile. I’ll also talk about how you can speed up the composting process and how to tell if your compost is done, so read on!

Stages of Compost

Whether you’re composting with or without a bin, the compost feedstock goes through three phases. 

During these phases, the composting feedstock made up of nitrogen-rich greens, carbon-rich browns, and moisture all breaks down to produce carbon dioxide, heat, water, and humus. The humus is the stable organic material that we can compost and later on use as a soil amendment and natural fertilizer. 

Let’s take a look at the three phases of composting:

Moderate-Temperature Phase

The first phase is the moderate-temperature phase, which is the initial decomposition

Microbes called mesophilic organisms inhabit the composting feedstock and start breaking the organic matter down. This phase is commonly known as the mesophilic phase after the organisms that do the work of decomposition at this time. 

In this phase, substances like starch and sugars are broken down, as they are the easiest to decompose. Temperatures in the compost pile can reach anywhere between 75-100 °F (24-38 °C) during the moderate-temperature phase. 

The moderate-temperature phase lasts a few days.

Most of the greens will still be recognizable at this phase, and the browns will be barely touched. 

High-Temperature Phase

The second phase is longer than the first and involves much higher temperatures, as the name suggests. 

The mesophilic organisms raise the temperatures steadily until it gets high enough for the thermophilic organisms to take over. During this phase, temperatures in your compost pile can reach between 110-150 °F (43-66 °C)

This phase, also known as the thermophilic phase, is the most active phase of composting. The heat produced during the high-temperature phase is essential for killing off any pathogens present in your compost, like eggs of fruit flies or other pests and any weeds. 

The remaining organic matter comprising proteins, fats, and cellulose is broken down during this phase, which can last for a few weeks, depending on the volume and composition of your feedstock. 

The compost starts gaining its rich, dark brown color and characteristic smell at this phase but will have a stickier, wet texture than the crumbly humus of completed compost. 

Cooling and Maturation Phase

The last phase is the cooling and maturation phase. It is usually at this point that most people start getting impatient and consider whether they can use partially decomposed compost. 

However, this phase, also known as the curing phase, is essential for the breakdown of the final bits of organic matter, including the carbon that the bacteria have been using as fuel. 

The maturation phase can last several weeks to several months and is the phase when the humus or the crumbly, sweet-smelling compost is finally produced. 

During the curing phase, all the ammonia compounds produced are processed by mesophilic organisms, ensuring that the final product is stable and easy to handle.

Speeding Up Compost

Composting is a slow process, but it doesn’t have to take several months. With regular attention, your compost can be completed in a span of a few weeks.

To speed up your compost, you can use a few easy tips:

Use More Nitrogen

Nitrogen is supplied by the ‘greens‘ in your composting feedstock. The greens are kitchen scraps and yard waste, including fruit and vegetable peels, grass clippings, and coffee grounds. The greens in your composting feedstock also supply moisture to your compost. 

Nitrogen is important as it is what contributes to the growth of the mesophilic and thermophilic organisms that we discussed earlier. More nitrogen means more microbes, which can then process and break down the feedstock into compost faster. 

It is important to remember that the greens should not overwhelm the browns. The ideal ratio of browns to greens is 3:1, so you should keep that balance even when you add more greens to supply nitrogen to the pile. 

The best way to add nitrogen without affecting the ratio of browns to greens is by using greens that are rich in nitrogen, like cow manure, chicken manure, and cull potatoes. These greens are richer in nitrogen than greens like kitchen scraps and will increase the overall population of composting organisms in your composting unit. 

Chicken manure also improves the effectiveness of the final product, producing compost with the least side effects and nitrogen loss. 

Chop Up Your Compost Scraps

Ensuring that your feedstock is torn or shredded into smaller pieces makes it easier for the mesophilic and thermophilic bacteria to break them down. 

Shredding your kitchen scraps also makes it easier for you to store your compost scraps in the freezer, which is a great way to avoid pests and bad odors in your kitchen. 

Make a Larger Compost Pile

The size of your compost pile matters. Too large, and your compost may overheat, killing off the beneficial organisms as well. Even thermophilic organisms can’t survive in temperatures above 150 °F (66 °C). 

However, the greater issue that most home composters face is a pile that’s too small. In a smaller compost pile, there will not be enough nitrogen or carbon to encourage the growth of composting microbes. This results in a cold composting process that will either take too long or stagnate entirely, resulting in too wet compost that may turn anaerobic.

Your compost pile should be a minimum of one cubic yard (0.76 cubic meter), which means that the pile should be 3 feet (0.9 meters) in height, length, and width.

If you’re short on space, then a narrow and tall pile is better than a wide and short pile, according to the University of New Hampshire.

Aerate Your Compost

Aerating your compost is as important as the greens, browns, and moisture of the compost feedstock. The organisms that process the feedstock and convert it into compost need oxygen to survive like any other living organism. 

Aerating your compost ensures that these microbes have enough oxygen to multiply and thrive in your pile and break it down faster. 

To aerate your compost, you need to maintain the ratio of browns to greens. You also need to layer them in the ‘lasagna layering‘ process, where you sandwich a thin layer of greens between two very thick layers of browns. This layering is done to ensure that the greens don’t stick together in a congealed clump as they decompose. 

The most important activity in maintaining your compost is turning your pile. This loosens up the particles of your compost, fluffs it up, and breaks up any lumps. The turning process also introduces fresh air into the pile, so the organisms can multiply and continue their work of converting the feedstock to compost. 

Cover the Compost Pile

Covering your compost pile helps insulate it, preventing excess moisture loss, so you won’t have to water your compost as often. 

The insulation of the pile is important to maintain the extremely high temperatures that compost can reach during its thermophilic phase. The insulation also supports the mesophilic phase and helps the compost continue to break down over the final cooling and maturation phase. 

Most large piles are self-insulating, but you can help your smaller piles along by covering them with a lid or an extra thick layer of browns on top

How Do You Know When Compost Is Done?

Completed compost is stable, easy to handle, and a great soil amender

Compost is done when it is a rich, dark brown color with a loose, crumbly texture. The finished compost will be sweet-smelling and will have reduced in volume by about 30-50%. The compost will feel cool to the touch, and none of the original feedstock will be recognizable. 

Completed compost is not as damp as compost in progress. While compost that is being processed should be about as wet as a wrung-out sponge, completed compost is slightly drier as the last of the greens and browns get processed into the homogenous brown humus of compost. 

The last of the maturation phase of composting occurs with mesophilic organisms, which means that the compost will still be warm in the last phase. Only when the compost has finished curing will it cool down completely, which is a good indication that it is ready to use. 

If you have large clumps in your compost feedstock that haven’t broken down, but the rest of the humus looks and feels right, you can throw them back into your compost pile. 

Final Thoughts

Compost should only be used when it’s fully decomposed to ensure that all pathogens, organic acids, and ammonia compounds have been fully processed and will not harm any plants or cause you to fall sick

To speed up compost, you should add greens that have more nitrogen, chop up your scraps, turn and aerate your compost, cover it to insulate it, and prevent moisture loss. The finished compost will be dark brown, sweet-smelling, and cool to the touch. 

Alexander Picot

Alexander Picot is the founder of and its lead content writer. He created the website in 2022 as a resource for horticulture lovers and beginners alike, compiling all the gardening tips he discovered over the years. Alex has a passion for caring for plants, turning backyards into feel-good places, and sharing his knowledge with the rest of the world.

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