Compost is decomposed organic matter used to enrich soil structure and provide plant nutrition. While the finished product is stable and does not “go bad” in the traditional sense of rotting, its quality can degrade over time. The composting process itself is susceptible to failure if organic materials stop decomposing correctly. Understanding the difference between a stalled process and a degraded product is the first step in successful composting.
Distinguishing Process Failure from Product Degradation
The term “going bad” applies differently to active piles versus finished compost. Process failure occurs when microbial activity in an active compost heap stalls or shifts to an undesirable anaerobic state. This failure to create the intended product is often due to an imbalance in materials or a lack of oxygen.
Product degradation, conversely, happens when cured, mature compost loses some of its beneficial qualities during long-term storage. For example, nutrient content can decrease, or the material can become structurally compromised. Finished compost is inert enough that it does not typically rot or become smelly again, but its utility as a soil amendment can diminish.
Signs of a Failing Active Compost Pile
A common sign of a failing process is the development of foul odors, indicating that the pile has become anaerobic. When oxygen is absent, a different set of microorganisms takes over, producing volatile, unpleasant byproducts like hydrogen sulfide, which smells like rotten eggs, or ammonia gas. An ammonia odor is often a sign of too much nitrogen-rich material, or “greens,” in the mixture.
Another clear symptom is excessive wetness or sliminess, indicating a moisture content above 65%. This excess water blocks air pockets, leading to anaerobic conditions and foul odors. The pile may also remain cold, failing to reach the thermophilic range of 131°F to 160°F necessary for rapid decomposition. Failure to heat up means beneficial heat-loving bacteria are inactive, and decomposition is stalled.
An imbalance can also be signaled by an overwhelming presence of pests like flies or rodents. These pests are often attracted to decomposing food scraps that are not breaking down quickly enough or are not properly covered by carbon-rich “browns”. When a pile fails to heat, it also fails to eliminate weed seeds and pathogens.
Issues Affecting Finished Compost Quality
Finished compost quality can degrade primarily through the loss of available nutrients. Nutrient leaching occurs when soluble elements, particularly nitrogen (nitrates), are dissolved by rain or excessive watering and drain away. Long-term storage in an uncovered area makes the material less nutritionally dense with each rain event.
Contamination is another issue if the initial pile did not reach sufficient thermophilic temperatures. If the pile never achieved the necessary heat, weed seeds and plant pathogens may survive in the finished product. Using this unpasteurized compost can unintentionally introduce undesirable elements into a garden bed.
Finished compost can also lose its beneficial structure, especially if stored in deep piles or confined containers. Over time, the material may compact, losing the desirable crumbly texture and air-holding capacity. This compaction reduces the porous nature of the material, making it less effective at improving soil aeration and drainage when applied to a garden.
Salvaging and Correcting Unusable Material
Correcting a foul-smelling, anaerobic pile involves aeration and the addition of dry, carbon-rich material. Turning the pile introduces oxygen, which encourages the beneficial aerobic microorganisms to resume activity. If the pile is too wet, adding absorbent “browns” like shredded paper, dry leaves, or sawdust will soak up the excess moisture and restore proper air flow.
To fix a cold pile that is too high in carbon, adding nitrogen-rich “greens” like fresh grass clippings or food scraps will fuel the microbes and help generate heat. The ideal ratio is typically between two to four parts brown material for every one part green material by volume. For cured compost that has lost nutrients from leaching, a simple fix is to mix it with a fresh batch of material or incorporate a balanced organic fertilizer before application.
Compost containing weed seeds or pathogens requires re-processing. This involves building the material into a new pile and ensuring it sustains temperatures above 131°F for several days, turning it regularly to expose all parts to the heat. This process effectively “resets” the material, ensuring the final product is safe for garden use.