How-to Guide
Why Your Compost Stinks and How to Fix It
The short answer
A well-run compost pile should smell earthy, so a strong odor is a diagnostic clue. A sharp, ammonia smell means there is more nitrogen (greens) than the microbes can use, and the excess is off-gassing as ammonia. A rotten-egg or sulfur smell means the pile has gone anaerobic, usually from being too wet or too compacted, so oxygen-starved microbes are producing hydrogen sulfide.
Both problems share a fix: add dry, carbon-rich browns and turn the pile to get air back in. For ammonia, mix in shredded leaves, straw, cardboard, or paper to rebalance the carbon-to-nitrogen ratio. For the rotten-egg smell, turn the pile to break up soggy compaction, add dry browns to soak up excess moisture, and cover fresh food scraps. Restoring oxygen and the brown-to-green balance clears both odors.
Ammonia smell: too much nitrogen
A pungent ammonia odor tells you the pile is overloaded with nitrogen-rich greens, things like fresh grass clippings, food scraps, and manure. When there is more nitrogen than the microbes can incorporate, the surplus escapes as ammonia gas, which also means you are losing nitrogen that should be feeding your compost. The fix is to add high-carbon browns and turn the pile to blend them in. Aim to rebalance toward a higher proportion of browns; shredded dry leaves, straw, shredded paper, and cardboard all work.
Rotten-egg smell: the pile has gone anaerobic
A sulfur or rotten-egg smell is the signature of anaerobic decomposition, which happens when oxygen can't reach the microbes, typically because the pile is waterlogged or packed down too tightly. Without air, different microbes take over and produce smelly hydrogen sulfide. Turn the pile to loosen it and introduce oxygen, mix in dry, porous browns to absorb excess moisture and create air pockets, and bury any exposed food scraps. If the pile is soaked from rain, adding dry material and turning restores aerobic conditions and the smell disappears.
Keeping a pile odor-free
- Maintain a good ratio favoring browns over greens; a common target is around three to four parts browns to one part greens by volume.
- Turn the pile regularly (roughly every one to two weeks) to keep it aerobic.
- Always cover fresh food scraps with a layer of browns rather than leaving them exposed.
- Keep moisture like a wrung-out sponge; add browns if it's soggy, water if it's bone dry.
- For the full method of building and maintaining a pile, see our composting guide.
Sources
Reviewed 2026-07-18. We cite university Extension, government, and established horticultural sources — and never invent pesticide rates or dangerous treatments.
- Cornell Cooperative Extension (Tompkins) - Troubleshooting Compost Piles — An ammonia odor indicates excess nitrogen and is fixed by adding carbon-rich browns; a putrid or rotten-egg odor indicates anaerobic conditions from excess moisture or compaction, fixed by turning and adding dry porous material.
- LSU AgCenter - How to Reduce Odor in Compost Systems — Compost odors come from too much nitrogen (ammonia) or from anaerobic conditions (sulfur/rotten egg); adding carbon material and aerating by turning restores balance and eliminates smells.