Cold Compost Analysis

Vance Murray, Ashley Amirault, Kella Elswick, Lanie O'Connor

Foundations

The Sustainable Agriculture Project (SAP) is where students can go to research plants, the environment, human-environmental interaction, and many others. Over the duration of the semester we have planted crops and cultivated them using sustainable practices. On the SAP we have access to the cold compost; the compost is made from scraps around the farm. It features a 'box' with slats to breath, turn, and remove the compost for our plots. While on the SAP the purpose of using cold compost was too see how it can benefit the user, the soil, and our community. We chose the Traditional Cold Compost because it is an accessible technique and it’s one of the simplest and most powerful actions individuals and communities can take to reduce waste and improve soil health.

Background Information

Black Spanish Radishes, grown at the SAP (Sustainable Agriculture Project), GVSU

The Importance of Microbes in Composting

Microbes consist of bacteria and other microorganisms that exist within compost piles. These micro-organisms are the ones who actually do the work of decomposing organic materials. Just like most organisms, microbes need a balance of nutrients, oxygen, and water to sustain their lives and functionalities.

Microbe production kicks into high gear when there is carbon present in the pile. Nitrogen is another important nutrient for microbes to be able to sustain themselves.

Carbon is an energy source for microbes and consists of almost half of the microorganisms' cell mass.
Nitrogen is a necessary element for cell growth and for fulfilling cell tasks.

There needs to be a particular ratio between the amount of each nutrient present in the compost pile for successful composting. If there is excessive nitrogen present, the nutrient is released from the compost pile as ammonia gas. If there is too little nitrogen, the microbes do not receive sufficient nutrients to fulfill their tasks, in this case decomposition.

Graduates from Cornell University recommend a C:N (Carbon:Nitrogen) ratio of 30:1 for productive composting.

Examples of Microbes

Bacteria

Has the most ample presence in the compost pile- consisting of 80-90% of available microbes.
Responsible for most of the decomposition process and heat generation.

Fungi

Consists of molds and yeasts.
Breaks down tough organic matter and debris, including materials that are difficult for bacteria to decompose.

Actinomycetes

Another form of bacteria that causes the rich earthy smell often associated with compost piles.
These bacteria work hard to break down the tougher materials in a pile, such as the bark of branches or woody stems.

Moisture & Temperature

Temperature, moisture, and oxygen levels are important factors to consider when it comes to composting. Water is important for feeding the microbes that assist in the decomposition of organic matter, and if there is not enough moisture present in the compost pile, the decomposition process slows down. On the other hand, too much water in the compost pile replaces space that should be reserved for air molecules. Microbes need both water and oxygen to do their jobs effectively. Oxygen can be added into a compost pile by adding medium to larger objects, such as broken branches. Composting is most effective when the temperature inside the pile is relatively warm, as higher temperatures increase the speed of decomposition.

Temperature recording of the cold compost pile at the SAP, GVSU

Hot vs. Cold Composting

Instructables: Hot compost pile

Hot composting

Hot composting has quicker results, though it is much more labor intensive and involves diligent observation and adjustment of input. This method requires high inputs of nitrogen-rich organic matter to heat the pile up, and will often produce results within a matter of weeks. The ideal C:N for hot compost piles are 2:1, with carbon inputs containing “brown” items like twigs, autumn leaves, and mulch, and nitrogen inputs containing “green” items, such as grass clippings and plant waste.

Cold composter pile at the SAP, GVSU

Cold composting

Cold composting takes much longer to achieve results, sometimes taking months or years to produce usable compost. The timing of this method depends on the amount of organic matter added to the pile and the size of the pieces. This method requires less intensive labor than hot composting, as there is no real process. Any loose plant or food scraps are simply thrown into a compost bin and left to sit for a long period of time. There is little need to check on this pile, though it will have quicker results if the organic matter is broken into smaller pieces, and if a C:N ratio is properly applied.

System Evaluation

Observations from September 29th to November 12th:

From our research and experience, we found that the most important part of ensuring a cold compost works is by adding in organic matter and layering green and brown materials. The most common ways to do this is through adding (green) plant/animal material like split tomatoes and flower stems, and (brown) yard waste/paper materials such as grass clippings and cardboard, and by alternating both.

Since cold composts rarely need to be turned, we tracked how long it would take the compost to form from September to November.

Although we did not get a picture of the compost at the start of our research, a student worker who was at the farm during both the summer and fall, testified that the last time the compost was turned was at the end of July, when temperatures were at their peak. At that time the active compost was only barely 1 wooden board high at about 8 inches. Now as can be seen in the photo below, the active compost is about 2 feet high and has doubled in the past 4 months. We believe this is because of the layering of different brown and green materials and the multitude of organic materials that have been added by us, the farm workers, and any other people at the farm. To finalize all the work that has come so far, the cold compost was winterized (covered with extra brown materials) to ensure that as much heat is trapped inside the compost to maximize compost production.

Some of the issues and recommendations of what could be done to help improve the cold compost are described in the following sections.

November 12th, 2025

Merits and Drawbacks

The Cold Composter we used is on the SAP near our plots and served as our basis of analysis. The composter features a large box with ventilation and removeable slats on the front side.

In practice, anyone can simply add kitchen scraps, leaves, and yard waste to the pile over time. This makes it an ideal method for beginners or those with limited time. Another advantage is that the cold composter preserves more nutrients, particularly nitrogen, which can be lost in the high heat of active composting. Additionally, because the process is slower and less intense, it supports a wider range of decomposers such as worms, beetles, and fungi, which promotes a burgeoning of biodiversity within the compost pile. Adding the compost and checking temperature were quite simple and manageable. Because the composter was uncovered, on days when it rained the water helped encourage decomposition without any additional effort.

On the other side of the coin, the two most notable shortcomings are the slow rate of decomposition and extracting usable compost from the bottom/middle. Even though we did not start the composter it can take a year or longer for materials to fully break down into usable compost. Also, the pile does not reach high temperatures, it may fail to kill weed seeds. The process is also less controlled, meaning that some materials, especially tougher plant matter or woody stems, may not decompose evenly and might need to be re-composted. In some cases, if food scraps are left exposed, the compost pile can attract pests such as rodents or flies. The next tribulation was accessing the desired compost due to the vertically removable slats on the front of the composter as the weight of the materials made it hard to move and replace the slats.

Recommendations

Based on the research we’ve done over the course of this semester our group has 3 main recommendations on how to improve the cold composter at the SAP.

Adjusting the Compost Access Point:

The current slat design makes it very difficult to access the finished compost at the bottom with the weight of the top materials. We recommend installing a hinged door system that could help allow easier access to the mature compost at the bottom without disturbing the active composition layer above.

Adding an Aeration System:

While cold composting requires minimal maintenance, aeration improves decomposition rates. We suggest incorporating tubes with holes into the pile which can be rotated to introduce oxygen without the turning required in hot composting.

Adding a Moisture Indicator:

Moisture balance is critical for microbial activity so we recommend adding a moisture meter or a color changing indicator at different depths to help us identify when watering is needed. This could help us maintain the optimal 40-60% moisture content without guessing.

Final Thoughts

Cold composting represents sustainability at its most accessible. The doubling of our compost pile from 8 inches to 2 feet over four months proves that patient, consistent action yields tangible results even without significant investment. Cold composting is something everyone can do at home and composting is so important when it comes to shifting our thought process from linear disposal to circular renewal. We challenge you to see organic waste differently. Whether you start with a small container in your backyard, join a community garden's composting program, or simply become more mindful of separating organics from trash, you're participating in a long going practice that is becoming more and more relevant each day.