Reference
Troubleshooting table
From what you see or smell to the likely cause, the first change and the check a week later, for piles, tumblers, worm bins and bokashi buckets.
Find the symptom, read the likely causes, make the first change, and check again in a week. Change one thing at a time so you can tell what worked. Most rows draw on the Kansas State, UC Napa and Oregon State troubleshooting guides for piles, on Oregon State, NC State and NYC for worm bins, and on NC State Beaufort, USask and WSU Kitsap for bokashi. The symptom names match the options on the problems sheet in the log, so you can record what you tried. The chapter explains how to work through it.
Likely causes are likely, not certain: two causes can give the same smell, and the first change is the cheapest one to try, not a diagnosis. The green box marks the rows that match the animals and pests you listed in setup.
| Method | Symptom | Likely causes | First change | Check a week later | Source |
|---|---|---|---|---|---|
| Slow pile, hot pile or enclosed bin | Rotten-egg or sour smell | Too much moisture, low oxygen or compacted material (Kansas State MF3371, UC Napa guide, Oregon State troubleshooting). | Turn the pile and mix in dry, bulky browns such as straw, dry leaves or shredded paper. Keep rain out with a tarp or a simple roof (Oregon State troubleshooting). If it is a very large pile, make it smaller (Kansas State MF3371). | Smell the pile and squeeze a handful at several depths: a few drops of water is the usual target. If the smell is still sour, repeat with more dry material. | Kansas State MF3371, UC Napa guide, Oregon State troubleshooting |
| Tumbler | Rotten-egg or sour smell | Too many greens or the wrong materials (LSU 3838-L); a tumbler that leaks dark liquid has a lot of wet food or grass in it (Oregon State tumbler answer). | Stop adding greens. Add dry browns to roughly equal the greens by volume (RDCK tumbler sheet), rotate to mix, and leave out meat, dairy and oily food. | Open it and smell. A drum that no longer leaks and smells earthy is balanced; if not, add more browns. | LSU 3838-L, Oregon State tumbler answer, RDCK tumbler sheet |
| Worm bin | Rotten-egg or sour smell | Overfeeding, food exposed to air, a bin that is too wet, items that do not belong, or too little air (NC State AG-473-18). | Stop feeding for two weeks, remove items that do not belong, bury the food under bedding, mix in dry bedding, and add air holes if the bin has few (NC State AG-473-18). Leave the lid off for a while (NC State AG-473-18). | Smell the bin and look for uneaten food. Resume feeding in small amounts only when most of the last feeding is gone. | NC State AG-473-18 |
| Bokashi bucket | Bokashi bucket smells foul | A foul smell instead of a sour, pickled one usually means too little bran (NC State Beaufort bokashi). Liquid left in the bucket also causes odors (WSU Kitsap bokashi). A sour, beery smell when you open the lid is normal (USask bokashi). | Add more bran, press out the air, drain the liquid, and keep the lid sealed between additions (NC State Beaufort bokashi, WSU Kitsap bokashi). | Open the bucket and smell: pickled or sour is the target. White mold on the surface is not dangerous and means the process is working (USask bokashi). Foul smell again: add bran again and check the seal. | NC State Beaufort bokashi, WSU Kitsap bokashi, USask bokashi |
| Kitchen container | Rotten-egg or sour smell | Scraps left in the container too long, or a container not washed (Portland compost tips). | Empty the container daily or every few days, or keep it in the freezer and empty it whenever you like. Wash it at least weekly (Portland compost tips). | Smell the container just before the next emptying. If it is clean-smelling, the routine fits; if not, shorten the time between emptyings or use the freezer. | Portland compost tips |
| Slow pile, hot pile or enclosed bin | Ammonia smell | Too much nitrogen, which means too few browns (Kansas State MF3371). Compacted leaves and too little air also appear in UC Napa guide. | Add browns such as sawdust, wood chips, straw or dry leaves, and turn the pile to add air (Kansas State MF3371, UC Napa guide). | Smell the pile. Earthy is the target. If ammonia returns, add more browns before adding any more food. | Kansas State MF3371, UC Napa guide |
| Tumbler | Ammonia smell | Too many greens in the drum (LSU 3838-L). | Add dry browns and rotate to mix. Pause new greens until the smell is gone (Kansas State MF3371 gives the same fix for piles). | Smell after a few rotations. Add browns again if the smell is still sharp. | LSU 3838-L, Kansas State MF3371 |
| Slow pile, hot pile or enclosed bin | Pile not heating | Pile too small, too dry, too little air, too little nitrogen, cold weather, or pieces too large (Kansas State MF3371, UC Napa guide). Oregon State troubleshooting says a pile of about 0.5 to 1 cubic yard that is well built should heat within a week. | Check size and moisture first. Add material to reach about a cubic yard, water while turning if it is dry, add grass clippings or other greens if it is mostly browns, and chop large pieces (Kansas State MF3371, Oregon State troubleshooting). | Read the center with a long-stem thermometer after a few days to a week. If it still does not warm, the pile may be too small to heat; a cool pile can still finish slowly. | Kansas State MF3371, UC Napa guide, Oregon State troubleshooting |
| Slow pile or enclosed bin | Pile not heating | A slow, add-as-you-go bin does not usually heat enough to kill diseases and weed seeds (Oregon State EM 9475); most piles do not (UVM Three Ways). This may not be a problem. | Decide whether you want heat. If you do not, change nothing and keep seeded weeds and diseased plants out. If you do, see The hot pile. | Note in your log that the bin is run cool on purpose, and check finished compost with the signs in Finished compost. | Oregon State EM 9475, UVM Three Ways |
| Slow pile, hot pile or enclosed bin | Pile not heating | Cold weather. A pile goes dormant in cold weather and starts again when air temperatures rise above about 50°F (Penn State home composting). | Keep adding scraps and covering them with browns. Insulate with a layer of leaves or other lightweight browns around and on top (New York DEC guide). A larger pile holds heat better (New York DEC guide). | Wait for spring warmth and check the center again then. | Penn State home composting, New York DEC guide |
| Tumbler | Pile not heating | Small two-chamber tumblers are too small to insulate themselves in a cold winter (Oregon State tumbler answer); a tumbler does not kill weed seed or pathogens in any case (LSU 3838-L). | Check moisture and the browns-to-greens mix first. Treat the tumbler as a cool method and keep seeded weeds and diseased plants out. | Check the mix and moisture again. If you want a hot batch, see The hot pile; a tumbler is run as a cool method. | Oregon State tumbler answer, LSU 3838-L |
| Hot pile | Hot only in the middle | Pile too small (UC Napa guide). North Dakota guide says a pile damp and warm only in the middle is too small. | Gather more material and rebuild a larger pile (UC Napa guide). | Read the temperature at several locations and depths with a long-stem probe (Cornell temperature). The edges are expected to read cooler than the center. | UC Napa guide, North Dakota guide, Cornell temperature |
| Slow pile, hot pile or enclosed bin | Too dry | Too much wood or too many dry browns, or too little water (UC Napa guide). Piles are most often too dry (NC State AG-791). | Moisten the material while you turn it, and add fresh green material (UC Napa guide, Kansas State MF3371). | Squeeze a handful at several depths. A drop or two of water is the target (NC State AG-791); add water again if it is still dry. | UC Napa guide, NC State AG-791, Kansas State MF3371 |
| Slow pile or hot pile in hot, dry weather | Too dry | Evaporation in a hot, dry climate. Arizona AZ1632 says the pile may need water weekly in summer. | Water the pile, cover it to slow evaporation, and move it to shade if you can (Arizona AZ1632). | Squeeze a handful a week later. If it dries between waterings, water more often or shade it more. | Arizona AZ1632 |
| Worm bin | Too dry | Bedding has dried out. The bin is too dry (NC State AG-473-18). | Dampen the bedding thoroughly, with a spritz and not a pour. Bedding should feel as moist as a wrung-out sponge (Oregon State EM 9034). | Feel the bedding and check where the worms are. If they have moved to the damp spots, the bin is still too dry in places. | NC State AG-473-18, Oregon State EM 9034 |
| Slow pile, hot pile or enclosed bin | Too wet or soggy | Too much water, too many wet greens, or rain. Excess moisture and low oxygen (Kansas State MF3371, Oregon State troubleshooting). | Mix in dry wood chips, cardboard pieces or newspaper strips (Cornell moisture), turn the pile, and cover it against rain (Oregon State troubleshooting). | Squeeze a handful. More than a few drops means it is still too wet; add more dry material. | Kansas State MF3371, Oregon State troubleshooting, Cornell moisture |
| Worm bin | Too wet or soggy | A bin that is too wet (NC State AG-473-18). Watery foods such as melon can add more moisture. | Mix in dry bedding and leave the lid off for a while (NC State AG-473-18). In a plastic bin, dry bedding absorbs the excess (Oregon State EM 9034). Mix wet food with bedding before feeding (NC State AG-473-18). | Feel the bedding. Wrung-out-sponge damp is the target. Check for pooled liquid at the bottom. | NC State AG-473-18, Oregon State EM 9034 |
| Tumbler | Too wet or soggy | Wet food or grass in the drum; a tumbler can leak dark liquid (Oregon State tumbler answer). | Add dry browns, rotate to mix, and leave out liquids. | Open the drum and squeeze a handful. Add more browns if it drips. | Oregon State tumbler answer |
| Bokashi bucket | Too wet or soggy | Liquid building up in the bucket (WSU Kitsap bokashi). | Drain the liquid every few days (WSU Kitsap bokashi, USask bokashi). USask adds a layer of dry sawdust or a false bottom to absorb extra liquid. | Check the spigot or the bottom of the bucket a few days later. No liquid should be standing against the food. | WSU Kitsap bokashi, USask bokashi |
| Slow pile or hot pile | Matted grass or leaves | Fresh grass clippings are wet and can mat into clumps with anaerobic pockets (UF problem materials). Compacted leaves also appear in UC Napa guide. | Break up the mat and mix in bulky browns such as wood chips, leaves or cut-up sticks. Build green layers no more than 1 to 2 inches thick (UF problem materials). Avoid paper as the main brown for a pile of clippings. | Dig into the layer a week later. It should be loose with no slimy clumps. | UF problem materials, UC Napa guide |
| Grasscycling | Matted grass or leaves | Clippings that clump after prolonged rain (Penn State clippings); mowing too seldom leaves large amounts of leaf residue (Penn State clippings). | Remove the clumps once they are dry and compost them or use them as mulch (Penn State clippings). Mow more often, taking no more than one-third of the plant height (UGA grasscycling). | Look at the lawn after the next mowing. Clippings should be short and disappear into the turf. | Penn State clippings, UGA grasscycling |
| Slow pile, hot pile or enclosed bin | Flies at an outdoor bin | Food scraps uncovered or too near the surface. | Cover each addition with browns: 4 to 8 inches (EPA, Composting at Home), or at least 4 to 5 inches on top to keep out flies (NC State handbook). Bury food scraps under at least 3 inches of browns (New York DEC guide). | Look for food at the surface and watch for flies. If flies persist, add more browns and check for meat or dairy. | EPA, Composting at Home, NC State handbook, New York DEC guide |
| Tumbler | Flies at an outdoor bin | Fruit flies can be worse in a tumbler because browns are mixed in instead of laid on top (RDCK tumbler sheet). | Add browns after each addition of scraps and work the scraps into the contents instead of leaving them on top. | Watch the door and vents for a week. If flies persist, pause adding fruit scraps. | RDCK tumbler sheet |
| Kitchen counter, container or compost bin | Fruit flies indoors | Breeding sites: ripe fruit, drains, garbage disposals, trash cans, bottles, mops and rags, forgotten potatoes and onions, a rarely emptied recycling bin (Kentucky fruit flies). A female lays about 500 eggs and egg to adult takes about a week (Kentucky fruit flies). | Remove the breeding sites and close or freeze the scrap container. Set a jar trap: a paper funnel in a jar with a few ounces of cider vinegar (Kentucky fruit flies). Empty the container every few days (Portland compost tips). | Count the flies in the trap after a week. Because the cycle is about a week, a week is the first check; if numbers do not fall, look for a breeding site you missed. | Kentucky fruit flies, Portland compost tips |
| Worm bin | Fruit flies indoors | Food exposed at the surface, or too many wet, nitrogen-rich scraps such as banana peels and melon (Oregon State EM 9034). | Bury food under bedding (1 to 2 inches, NC State AG-473-18), cover with damp newspaper or cardboard, freeze fruit before adding it, set a cider vinegar or wine trap beside the bin, and pause feeding for two to three weeks if needed (Oregon State EM 9034, NYC worm bin brochure). | Look at the surface and the trap after a week. Fewer flies and no exposed food mean the change worked. | Oregon State EM 9034, NC State AG-473-18, NYC worm bin brochure |
| Bokashi bucket | Fruit flies indoors | A bucket that is not fully sealed or food left exposed while you add to it. NC State Beaufort describes the sealed process as deterring rodents and flies (NC State Beaufort bokashi). The cause here is a likely one, not a certain one. | Press the lid down fully after each addition, cover the top layer with bran, and check the seal. Use a jar trap near the bucket (Kentucky fruit flies). | Check the seal and the trap after a week. | NC State Beaufort bokashi, Kentucky fruit flies |
| Slow pile, hot pile or enclosed bin | Rodents or other animals | Meat, fatty food or uncovered scraps (Kansas State MF3371, UC Napa guide, Oregon State troubleshooting); gaps in the bin; no floor. The cause may also be the neighborhood and not your bin. | Stop adding meat, dairy and grease. Bury food scraps under 3 inches or more of browns (New York DEC guide). Close gaps larger than 1/4 inch and line the bottom with hardware cloth (EPA, Composting at Home, Oregon State EM 9475, Cornell urban farming guide; New York DEC guide gives 1/2 inch). This manual does not teach poisons or traps. | Look for droppings, digging and chewed material after a week. If animals persist, ask your landlord, a licensed pest professional or your city. | Kansas State MF3371, UC Napa guide, Oregon State troubleshooting, New York DEC guide, EPA, Composting at Home, Oregon State EM 9475, Cornell urban farming guide |
| Worm bin, outdoors | Rodents or other animals | A bin that is not rodent resistant, or meat, dairy or grease in it (Oregon State EM 9034). | Use a bin with no holes or gaps larger than 1/4 inch and remove meat, dairy and grease (Oregon State EM 9034). Oregon State's table also lists traps or baits; this manual does not teach them. Ask your landlord, a licensed pest professional or your city. | Check the bin for gaps and signs of entry after a week. | Oregon State EM 9034 |
| Any outdoor bin or pile in bear country | Rodents or other animals | Food scraps and fruit smell strong to bears. Montana lists compost piles among attractants (Montana FWP). | Follow your state wildlife agency's advice first. Vermont's agency advises an enclosed container that would be hard for a bear to open, with tumblers especially hard for bears, no meat scraps or bones, and stopping home composting or using an electric fence if a bear is around (Vermont Fish & Wildlife); Colorado advises an enclosed system and no meat or fruit scraps on the pile (Colorado Parks and Wildlife). | Bear guidance is local; ask the wildlife agency what to check and how often. | Montana FWP, Vermont Fish & Wildlife, Colorado Parks and Wildlife |
| Trench or buried bokashi | Rodents or other animals | Buried food that is too shallow or in reach of raccoons, possums or groundhogs (Maryland how-to). | Bury at least 8 inches deep (NC State Beaufort bokashi) or fence the garden (Maryland how-to). Leave meat and dairy out of plain trenches. | Look for digging a week later. Rebury and add depth if the site was disturbed. | Maryland how-to, NC State Beaufort bokashi |
| Worm bin | Worms trying to leave | Bin conditions are not right: too wet, too dry, extreme temperature, too little air or too little food (NC State AG-473-18). Vibration near a washer or dryer can also push worms to escape (Oregon State EM 9034). | Check the moisture, the temperature (about 59 to 77°F, NC State AG-473-18), the air and the food. Leave the lid off and the worms will burrow down (NC State AG-473-18). Move the bin away from vibration. | Count how many worms are outside the bin after a week. Fewer escapes mean the cause was found. | NC State AG-473-18, Oregon State EM 9034 |
| Worm bin | Worms not eating | A new bin; too cold, since worms feed less below 50°F (Oregon State EM 9034); too much food left uneaten; or bedding too dry or too wet. | Stop adding food until most of the last feeding is gone. Start at 1/4 to 1/2 pound of food per pound of worms a week (Oregon State EM 9034). Check the temperature and moisture. | Check how much food is left a week later. Feed again only when most of it is gone. | Oregon State EM 9034 |
| Any method | Other | Unknown. Some sights are normal: sowbugs, millipedes and other small animals in a pile (Cornell invertebrates), and white mold on a bokashi bucket (USask bokashi). | Something not listed: describe it, change one thing, check in a week. Write it on the problems sheet in the log. | Check in a week. If nothing changed, change one other thing, or ask your extension office. | Cornell invertebrates, USask bokashi |
Limits
The table lists likely causes, not certain ones. A rodent problem may be the neighborhood's and not your bin's, and pest control beyond the bin belongs to your landlord, a licensed pest professional or your city. This manual does not teach rodenticides, poisons or traps, and it does not advise using them. In bear country, your state wildlife agency's advice comes before the table's. If a symptom stays after two changes, or you are unsure what you are seeing, ask your local extension office.
Where these come from. University extension and agency guides, each linked in its row and fetched on 2026-10-26. Where Oregon State's own worm bin table lists a trap or bait for rodents, the row says so and leaves it there. The three piles troubleshooting guides are compared in Troubleshooting under Go deeper.