You may think decaying organic waste smells rotten, but in compost, it shouldn’t! Composting microorganisms like fungi, bacteria, and archaea eat the debris before it smells bad. They work with worms, beetles, and fly larvae to turn apple cores, plant clippings, and leftover food into rich, crumbly, humus-rich soil.
Decay can smell bad but this typically results from slower-working natural processes that lack oxygen, causing anaerobic decomposition. This is why turning your compost is crucial for quick breakdown rates—it ensures the good-smelling microbes have enough oxygen to thrive and keep anaerobic ones out.
When compost is too wet, has large chunks, or has an imbalance of green and brown materials, it may stink rotten. We’ll use simple methods to turn slow-working, stinky piles into hot, quick-acting, and good-smelling ones. With continuous attention and care, the material will break down so quickly and beautifully that you’ll hustle to replenish them!
Where Bad Smells Come From
There are many common sources of bad composting smells, but they’re easily fixable once you know what’s going wrong. First, study your rotten pile to find the cause, and then you’ll know what techniques will fix it.
These are three common reasons compost piles smell acrid.
Anaerobic Decomposition
Anaerobic decomposition is a waste breakdown process like composting, but it only occurs when oxygen is absent. If you have a bin in your kitchen for food scraps, you may notice smells stemming from this natural process. It causes slime, mold, and other various organisms to start working that release rotten aromas readily.
Outdoors, anaerobic decomposition occurs when decomposing materials sit without turning or adequate balance. Their centers grow devoid of air as the microbes use it during their eating processes. When they die from a lack of airflow, anaerobic microbes take their place. These less-than-desirable organisms thrive if the pile remains static without turning or venting for airflow.
Anaerobic decomposition is useful for the environment but doesn’t belong in your compost! Reduce this natural process outdoors with regular turning, compost vents, or bins with holes on the sides that facilitate better airflow. Indoors, try bokashi composting to reduce odors until you can transfer the food scraps outdoors.
Slow Rotting Waste
Some objects decay slower than others, like meat, large branches, and big debris chunks. When your compost has these waste items and lacks turning or has improper levels of greens, browns, and moisture, it’ll start to smell weird. Sometimes rodents or squirrels disturb composting heaps in search of tasty treats. Their meddling may redistribute the inputs, causing them to decompose slower than normal.
One major cause of slow rotting compost is large particles. The bigger things are, the longer it takes worms, larvae, and microbes to eat at their center. Chop up food scraps, plant stems, and branches so they’re small for these critters, and they’ll digest them before they start smelling bad.
Some items like dairy products, meat, and cooked meals may take longer to decompose than simpler things, and you should only add them in small quantities. If you see an excess of them, hold off on adding any more until the current material decomposes.
Meats and dairy products can put your pile at risk of contracting diseases. E. coli and Salmonella from improperly decomposed meat and dairy can make their way into the garden when you add compost from the pile they were in. If you’re unsure about proper management of dairy and meat, avoid adding either to your pile.
The final cause of slow rotting is too much or little moisture. You’ll want your compost heap to have 50% water, so it resembles a wrung-out sponge.
Nutritional Imbalance
Piles may struggle to decompose if they lack a healthy balance of green and brown materials. Greens are fleshy objects with lots of nitrogen, like food scraps, plant clippings, and lawn leftovers. Brown materials are rich in carbon—dried leaves, twigs, and straw are some common examples.
| Browns | Greens |
| Straw | Kitchen scraps |
| Fallen, or dry leaves | Grass clippings |
| Twigs and branches | Green plant debris |
| Chemical-free paper | Manure |
You’ll want the proper ratio of greens to browns to achieve a healthy balance. This ratio ensures your composting microbes and worms have the nutrients they need to continue thriving and decaying waste. Roughly one part greens to two or three parts browns is ideal, but if your compost isn’t heating up, you can add more greens. The ratio may vary depending on the inputs.
How To Fix It
Now that we know what causes rotten smells, we’re ready to fix it. You’ll need a pitchfork, a hose or sprinkler, and an attentive eye. Study your heaps closely, and they’ll signal what they need by falling apart, staying static, or smelling bad. Use these steps to get them back on track.
Step 1: Aerate (Flip)
The best, most efficient way to ruin putrid smells is with regular turning. Turning a compost pile consists of stabbing it with a pitchfork, lifting chunks of it, and turning them over. This process boosts composting activity with a fresh supply of air and puts the microbes in contact with new particles that still need to break down.
Hot compost needs daily turning, while cold compost needs biweekly or monthly action. If your cold compost pile smells, it’s most likely due to anaerobic decomposition from a lack of airflow. Turn your heap, monitor it for smells, and turn it again if they come back.
If you don’t have a pitchfork, you may use a shovel, rake, or broad fork to flip the materials. It won’t be as easy, but it’s still manageable. The goal here is to reshuffle the debris so that air stays inside the heap, and so worms and microbes can eat undecayed items. Use your tools however you can to accomplish this turning action.
Step 2: Maintain Consistent Moisture
Alongside regular turning, consistent moisture ensures microbes, worms, and larvae have a pleasant environment to thrive and reproduce. With not enough water they dry out; with too much they drown. Aim for 50% moisture because that’s the ideal range for proper composting.
In fall and spring, maintaining moisture is no problem—rainfall and mild, warm temperatures help keep it steady. Summer is when you’ll have trouble, as heat waves and droughts threaten your compost’s life. You may have to water it twice a week or more in hot seasons and less than once every week or two in mild ones.
If there’s too much moisture right now, hold off on watering it until it dries, then turn the material. Turning facilitates drying by exposing more particles to the outside air. Fix excessive dryness by spraying with a hose or sprinkler until the moisture is like a wrung-out sponge. Test this by grabbing a clump of compost and squeezing it. If water comes out, then it is wet enough!
Step 3: Balance Greens and Browns
Nutritional imbalance leads to weak or nonexistent microbes as they struggle to eat a well-balanced diet. You’ll want to add greens and browns in the proper ratio to your. If you’re measuring by weight, 30 parts carbon to one part nitrogen maintains a healthy balance for composting organisms. But if you’re measuring by volume, this comes out to about two to three shovels of browns for every one shovel of greens.
If your pile isn’t decomposing, is drying quickly, and lacks worms or larvae, it needs green materials. If it’s stinky, slimy, and wet, it needs brown materials. Keep adding both types until you reach a good balance, then water until it’s 50% moist.
Before adding any materials, inspect the waste to ensure it consists of small particles. If there are large chunks, use a shovel or pitchfork to break them into smaller pieces. Even with a perfect one-to-one ratio, large particles will cause composting imbalances, and it’ll slow down decomposition. Small chunks ensure the mulch breaks down quickly and efficiently without putride aromas.
After turning and steady decomposition, ratios may change over time. Watch them closely and inspect after turning to see if they need greens or browns. Stop adding new materials two to three weeks before you want to harvest your hot compost. For cold piles, cease all debris additions three to six months before harvesting them.
Step 4: Relocate
If all else fails, your heaps might be in a bad spot for efficient composting. Compost needs partial shade to thrive—too much or too little sunlight causes issues with the microorganisms and small creatures that live inside it. Sometimes a simple relocation fixes bad smells.
If you live in a rainy climate, you’ll want to decompose under cover so the material doesn’t get too wet. Evergreen trees, garden structures, and bins help protect them from excess moisture. If you live in a hot and dry climate, shady conditions are beneficial, especially during the afternoon’s intense heat.
Relocate your pile by taking chunks of it with a pitchfork from the old site to the new one. Do so until you rearrange all parts to make a new heap. If there’s black, crumbly compost on the bottom of the old site, use it as mulch or fertilizer! Ready compost collects at the bottom naturally.
Step 5: Monitor For Changes
A good rule for composting is to check on your mounds at least once a week. If you’re making hot compost, you can check daily when you turn them. If you still notice rotten, bad smells, check for the three root causes above, then complete steps one through four as necessary. You can never completely ruin your compost—it usually just needs a little love to start again.
While harvesting compost, leave a little bit of the finished product behind. It’ll act as an inoculant for any new mounds you form, and help keep acrid smells away in the future. Keep encouraging those beneficial microbes, worms, and fly larvae so you’ll never have a rotten pile again!
