Composting is the natural process of recycling decomposed organic matter into a nutrient-rich soil amendment. A successful, finished batch should be dark brown, crumbly, and possess a pleasant, earthy aroma, similar to a forest floor after rain. The process relies on aerobic microorganisms breaking down material efficiently. If your pile looks slimy, fails to heat up, or develops an acrid smell, the decomposition has stalled or gone wrong. Identifying these signs is the first step toward correcting the imbalance.
Odors Signaling Anaerobic Breakdown
The most immediate sign of a problem is a persistent, foul smell emanating from the pile. These odors signal that beneficial aerobic decomposition, which requires oxygen, has been replaced by an anaerobic process occurring without air. One common sign is a pungent, sharp smell resembling ammonia, which occurs due to an excess of nitrogen-rich materials, often called “greens.” When the carbon-to-nitrogen ratio is too low, microbes cannot utilize all the nitrogen, causing the excess to gas off as ammonia.
A different, but equally concerning, odor is the smell of rotten eggs or sewage. This stench is caused by the release of hydrogen sulfide gas. This gas is a byproduct of anaerobic bacteria thriving in conditions that are too wet and compacted. These conditions effectively drown out the oxygen required by healthy microbes, indicating a severe problem.
Visual Cues and Texture Problems
Beyond the smell, the physical state of the material provides clear evidence that the process is failing. If the pile is excessively wet, it may develop a slimy or matted texture, particularly in the center. This results from a lack of air pockets, leading to waterlogging and compaction that stifles microbial activity. Matting frequently occurs when wet materials like fresh grass clippings are added in thick layers, forming a dense barrier that prevents air circulation.
Another indicator of a stalled process is the material’s color and consistency, which should become uniform and dark over time. If recognizable food scraps or bright green garden waste remain unchanged, breakdown is not occurring efficiently. The presence of certain types of mold, such as slimy or green-colored fungus, can signal excessive moisture. This differs from thin, white, thread-like strands, which are beneficial actinomycetes—a type of bacteria that helps break down tough, woody materials.
A cold core within the pile, even when the ambient temperature is warm, is a significant problem sign. Active composting is a biological process that generates substantial heat, often reaching internal temperatures between 130°F and 160°F. A pile that remains cold indicates that the microorganisms responsible for decomposition are inactive due to a lack of moisture, insufficient nitrogen, or the pile being too small to retain heat.
Diagnosing the Imbalance and Simple Solutions
The specific smell or visual cue can pinpoint the imbalance that needs correction. If the pile smells strongly of ammonia, the root cause is an overabundance of nitrogen-rich material. To fix this, immediately incorporate a large amount of carbon-rich “brown” materials, such as dried leaves, straw, or shredded paper. Turn the pile thoroughly to mix them in, which increases the carbon-to-nitrogen ratio and stabilizes the excess nitrogen.
When the compost is slimy, putrid, or smells of rotten eggs, the issue is excess moisture and lack of oxygen. The solution requires aggressive aeration by turning the pile with a fork to introduce air and break up compacted areas. Simultaneously, add dry, absorbent material—like sawdust, dry leaves, or shredded cardboard—to soak up the excess water and restore the air-to-solid ratio. If the pile is dry and cold, decomposition has halted due to lack of moisture. In this case, add water until the material feels like a wrung-out sponge, then turn the pile to distribute the moisture and reignite microbial activity.