Compost manure is a highly beneficial soil amendment created by combining animal waste with high-carbon organic materials and allowing them to decompose under controlled, aerobic conditions. This process relies on microbial activity to transform raw waste into stable, nutrient-rich humus. Properly managed composting significantly reduces pathogens and weed seeds while stabilizing nitrogen, making the final product valuable for agriculture and gardening.
Selecting and Balancing Raw Inputs
Successful manure composting begins with the careful selection of both nitrogen-rich and carbon-rich components to fuel the microbial decomposition process. Common sources of nitrogen include livestock manures from horses, cows, and chickens, each offering a slightly different moisture and nutrient profile. However, it is important to avoid using manure from animals that have recently consumed hay or feed treated with persistent herbicides, such as aminopyralid, as these chemicals can survive the composting process and damage future crops.
The necessary carbon sources, often called “browns,” provide the structural material for the composting microbes and include materials like dry leaves, straw, shredded paper, or wood chips. A proper ratio between the carbon (C) and nitrogen (N) content is needed to ensure rapid decomposition, with an ideal C:N ratio falling between 25:1 and 30:1. If the ratio is too low (excess nitrogen), the pile will release ammonia odor; if it is too high (excess carbon), decomposition will slow significantly.
While precise laboratory testing is not practical for the average user, the ratio can be estimated by volume, aiming for roughly two parts brown material for every one part manure. Different manure types also vary; chicken manure is generally richer in nitrogen than horse manure, meaning it requires a larger volume of brown material for balance.
Before building the pile, all materials should be prepared by shredding or chopping large pieces to increase the surface area available to the microbes. This initial preparation, along with ensuring the mixture has a moisture content similar to a wrung-out sponge, primes the environment for decomposition.
Building and Actively Managing the Pile
The physical construction of the pile must provide sufficient mass to insulate and retain the heat generated by microbial activity, which is the engine of the composting process. A minimum dimension of approximately 3 feet by 3 feet by 3 feet is generally required to achieve and maintain the necessary temperatures. The pile should be built in layers, alternating between the nitrogen-rich manure and the carbon-rich browns, which helps distribute nutrients and promotes even decomposition throughout the structure.
Once constructed, the pile enters the thermophilic, or “hot,” phase, which is when the most important biological work occurs. Monitoring this temperature is paramount and requires a long-stemmed compost thermometer inserted deep into the center of the pile. The temperature needs to reach a minimum of 131°F (55°C) and ideally stay below 160°F (71°C) to effectively destroy most common pathogens and weed seeds.
Maintaining this high heat requires regular aeration, which is achieved by physically turning the pile to introduce oxygen and redistribute materials. During the active hot phase, turning should occur every three to seven days, particularly whenever the internal temperature begins to drop below the 131°F minimum.
Turning also provides an opportunity to manage the moisture content, which can be lost quickly due to the high internal temperatures. If the material appears dry during turning, water should be added until the wrung-out sponge consistency is restored, as microbial activity slows significantly in dry conditions. If the pile quickly cools after turning, it may indicate that the carbon-to-nitrogen ratio needs adjustment, potentially by adding more nitrogen sources.
Curing, Testing, and Safe Application
The end of the thermophilic phase signals the transition to the final stage of stabilization and maturation, which is indicated by the pile’s inability to reheat after turning. Once the temperature remains stable and close to the ambient air temperature, the rigorous management of turning and monitoring is no longer necessary. At this point, the compost should exhibit a dark, crumbly texture and possess a pleasant, earthy smell, completely lacking any odor of ammonia, sourness, or the original raw manure.
This stable, partially decomposed material must then enter the curing phase, a period where it is left unturned for approximately four to eight weeks. Curing allows the remaining organic acids to break down and for the beneficial microbial community to fully stabilize the nutrients into forms readily available to plants. Applying compost before this curing period is complete can potentially harm plants due to residual organic acids or incomplete stabilization of nitrogen compounds, leading to nutrient tie-up.
This heat treatment converts potentially hazardous raw manure into a safe soil amendment suitable for use in vegetable gardens and flower beds. When applying the finished compost, it should be mixed into the top few inches of soil or used as a nutrient-rich top dressing around established plants. This application method ensures that the stable organic matter and nutrients are incorporated directly into the root zone, improving soil structure and water retention capacity over time.