Manure is a powerful organic resource that has been used for centuries to enrich garden soil. It adds organic matter, improves soil structure, and supplies plants with necessary nutrients. Aged manure refers to material that has decomposed over time, transforming it into a stable and safe soil amendment. This provides a slow-release source of fertility and enhances the overall health of the soil ecosystem.
Fresh Versus Aged Manure
The difference between fresh and aged manure centers on stability and safety for immediate garden use. Fresh, or raw, manure contains high concentrations of soluble salts and nitrogen compounds, often as ammonia. These high levels can cause “burning,” or chemical damage, to plant roots and foliage if applied directly. Fresh material also has high moisture content, a dark color, and a strong odor.
Aged manure has undergone partial decomposition, stabilizing the nutrient content. The volatile nitrogen has off-gassed, and the salt concentration is reduced, making it safer for plants. Fresh manure also carries a higher risk of containing viable weed seeds and harmful pathogens. Aged manure has a light, crumbly texture, a rich brown or black color, and an earthy smell, indicating the organic matter has begun its transformation into humus.
The Transformation Process
The creation of aged manure is achieved through a natural decomposition process, which is essentially a form of composting. The transformation begins when manure is piled, allowing microorganisms to break down the complex organic materials. Actively managing the pile through composting accelerates the process significantly compared to simply letting it sit.
For the quickest and safest results, the process requires balancing carbon-rich materials, like straw or wood shavings, with the nitrogen-rich manure. The ideal carbon-to-nitrogen ratio ensures the microbes have the energy needed for efficient breakdown. The pile must be kept consistently moist, feeling like a wrung-out sponge, and aerated by turning it every one to two weeks.
This active management, or “hot composting,” allows the internal temperature of the pile to reach between 130°F and 140°F. Sustaining this high temperature kills parasites, weed seeds, and most harmful pathogens. While manure can become ready in as little as eight weeks with frequent turning, a full curing period of six months to a year is often recommended for maximum stability. The material is considered finished when it no longer heats up after turning, has a uniform texture, and smells like forest soil.
Application Methods for Soil
Once the manure is properly aged and has a stable, crumbly texture, it can be safely incorporated into the garden. The primary application method involves working the material directly into the soil before planting. For vegetable beds, spread a layer of about one-half to one inch deep across the surface. This layer is then incorporated into the top three to four inches of existing soil, which helps improve structure and water retention.
For established plants, aged manure can be used as a top dressing or side dressing, especially for heavy feeders like tomatoes or corn. The material is spread around the base of the plants, acting as a slow-release fertilizer and a surface mulch. The nutrients gradually leach into the root zone with watering and rain, while the layer helps suppress weeds and conserve soil moisture. Applying aged manure in the fall is common, allowing the material to fully integrate over the winter months, setting the stage for a productive spring.