A single 1,000-pound horse generates 40 to 50 pounds of manure daily, creating a significant waste management challenge, especially when soiled bedding is included. Composting this material is the most effective way to transform a disposal problem into a valuable, nutrient-rich resource. This process of managed biological decomposition results in a stable, soil-like amendment that significantly improves garden soil structure and water retention.
Essential Materials and Pile Construction
Building a successful compost pile begins with managing the balance between carbon and nitrogen sources, the Carbon-to-Nitrogen (C:N) ratio. The microorganisms that drive decomposition require a C:N ratio between 25:1 and 30:1 for optimal activity. Raw horse manure is relatively nitrogen-rich, often having a ratio close to the ideal range.
However, mixing manure with carbon-heavy bedding materials, such as wood shavings, sawdust, or straw, skews this ratio significantly. If too much carbon is added, decomposition slows down, and the pile may struggle to heat up. To counteract high carbon content, materials like fresh grass clippings or spoiled hay can be incorporated to boost the nitrogen level.
Pile construction is important for initiating the thermophilic, or heat-producing, phase. The pile must be large enough to generate and hold heat, requiring a minimum size of three feet wide, deep, and high. Selecting a level, well-drained composting site prevents nutrient-rich liquid, known as leachate, from running off. Positioning the pile away from horse barns can also help reduce fly activity.
Monitoring and Turning the Compost Pile
Once the pile is built, the active composting phase requires careful monitoring to ensure the process destroys pathogens and weed seeds. Decomposition generates heat, and the internal temperature must reach and maintain a range of \(130^{\circ}F\) to \(160^{\circ}F\). Reaching at least \(131^{\circ}F\) for a minimum of three consecutive days is the recognized standard for killing most undesirable organisms.
Temperatures are measured using a long-stemmed compost thermometer inserted deep into the center of the pile. If the temperature climbs above \(160^{\circ}F\), the pile risks overheating and killing the beneficial bacteria and fungi. Turning the pile is the primary method used to manage temperature and re-introduce oxygen, which the microbes consume rapidly.
Turning ensures that all material, including the outer, cooler layers, is moved into the hot core to complete sanitization. Turning is recommended whenever the temperature starts to drop or exceeds \(140^{\circ}F\). Maintaining a proper moisture level is equally important; the material should feel damp but not soggy, similar to a wrung-out sponge. If the material is too dry, decomposition will slow down, and water should be added during turning.
Addressing Specific Concerns in Horse Manure
The sustained heat achieved during composting is necessary to mitigate biological risks unique to horse manure. This includes the eggs of equine parasites and the numerous weed seeds that pass undigested through the horse’s digestive system. Without reaching the \(131^{\circ}F\) threshold, these organisms can survive and contaminate garden beds.
A significant concern is the presence of persistent herbicides, such as aminopyralid or clopyralid, which may be present in the hay or straw fed to horses. These chemicals are designed to resist breakdown and can pass through the animal, remaining active in the finished compost. Unlike pathogens, these herbicides are not reliably destroyed by the composting heat and can persist for years.
When applied to a garden, contaminated compost can severely damage broadleaf plants, including sensitive vegetables like tomatoes, beans, and potatoes, causing twisted leaves and poor yields. Composters should investigate the source of their hay and bedding to avoid these residues. A simple test, such as planting a few bean seeds in a small sample of the finished compost, can help detect contamination before the material is used extensively.
Recognizing Finished Compost and Its Uses
The final stage of the process, known as curing, begins when the pile’s temperature no longer rises significantly after turning. The material enters a maturation phase where it cools down to near the ambient air temperature. This cool-down period allows the remaining organic matter to stabilize fully, preventing the finished compost from tying up nitrogen in the soil when applied.
Finished compost will exhibit several distinct changes in appearance and texture. It should have a dark, rich brown color, a pleasant, earthy smell, and a crumbly texture. The original components, such as individual pieces of straw or bedding, should be largely unrecognizable.
Once the material is cured and stable, it can be used as a versatile soil amendment. It is excellent for enriching vegetable garden beds by mixing it directly into the top few inches of soil before planting. Finished horse manure compost also works well as a top dressing for lawns or flower beds, providing slow-release nutrients and retaining moisture near the roots. Cured compost can also be incorporated into a soil mix for container gardening.