Troubleshooting during composting process

By | November 26, 2020

Troubleshooting during the composting process

Composting isn’t an exacting science. It happens naturally in our backyard heaps, just as it does on every forest and prairie floor. While maintaining ideal temperatures in a bin or pile takes some attention, the problems that arise when making compost are few and the solutions are many. Here, when needed, are the problem solvers.

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If a compost pile smells, something is wrong. Ordinarily, composting does not smell. Mostly two sorts of smells — rot and ammonia — afflict a pile, and since these have clear and distinct causes, they’re actually quite easy to diagnose and treat.

Rotten Smells

A compost pile that smells like rotten eggs or rotting vegetables has gone anaerobic. This means that there is not enough oxygen to support aerobic microbes and the anaerobic ones have taken over. Unfortunately, they produce hydrogen sulfide as a by-product, and hydrogen sulfide smells like rotten eggs.


The solution is simple: turn the pile. This may be unpleasant since it requires that you get up close with the odiferous heap. But it’s well worth it. Rebuild your turned pile on a palette to promote bottom-up airflow. Or work some large sticks into the middle of the heap to give it support. If the pile keeps reverting to an anaerobic mode, it’s time to explore different ingredient ratios or composting styles. Some methods including sheet composting don’t let too much of the wrong materials build up and begin to smell. The trench composting method smothers odors by moving the process underground.


Compost piles smell like ammonia when they give off excess nitrogen (N) in the form of ammonia (NH3). This problem occurs most often if a composter has been adding high-nitrogen products. The smell signals that the pile has a surplus of nitrogen from too many green materials.

The short-term solution is to turn the pile or even spread it out to allow the excess ammonia to vaporize. Mixing in brown material can also restore the carbon-nitrogen balance. The long-term lesson is to restore the carbon-nitrogen balance. Increase carbon or brown materials, by adding straw, sawdust, peanut shells, or shredded, unbleached, or colored cardboard to the pile. Mix them in well. In the future, add less nitrogen.

The Pile Won’t Heat Up

You heard about hot compost piles, maybe even seen one. But yours never does. Why? Is the hot pile a myth? No. But it takes some planning and effort to achieve. Supply all the conditions and ingredients it needs and the heat will be on.

Old, Unmaintained Piles

First off, it’s important to realize that only a freshly built or freshly turned pile will get hot. Continuous piles — unmaintained heaps that get new stuff added to them continually over the year — will not heat up. There may not be enough nitrogen. The oxygen supply at the bottom may have been depleted over time. Even if the carbon-nitrogen and moisture balance in the new material is perfect there may not be enough of it, depending on the size of the original heap, to support the mass of microbes needed to create a hot pile.

There are two ways to heat up such a pile: add an enormous amount of new material on top, or turn it. The first solution is equivalent to building a new pile on top of the old one, but building it with an eye to heat. As the new material heats up and is turned into the rest of the pile it will raise the temperature of the old material as well.

The second method, simply turning the pile, maybe all it takes. But if it’s either too wet or too dry or if it lacks nitrogen throughout, you can turn and turn and the thing will still not heat up. If moisture drips out when you squeeze a handful of material, it’s too wet. You can spread it out to speed evaporation, you can turn daily, or you can just wait for dry summer weather. If the material doesn’t look and feel damp, it’s too dry. Water it.

If you’re fairly sure that moisture isn’t the problem, try adding nitrogen. This is best done when you turn it as you can incorporate grass clippings or corn gluten meal or blood meal here and there, ensuring an even distribution.

Converting a cool pile to a hot one takes some work — but it can be done.

Newly Built Piles

You build what’s supposed to be a hot pile. You wait and … you wait. The stuff settles a bit over the first week and then just sits there. The thermometer you stick in it barely moves. What’s the problem?

There are several possibilities. Lack of moisture, nitrogen, oxygen or micro-organisms will all cause the composting process to stall out. The real problem is figuring out which item is missing from your pile.

Size: Below a certain size (a certain surface-to-volume ratio), piles won’t really heat up. If your pile contains less than about a cubic yard of material, it probably won’t heat up. Make sure the area where it rests measures at least 3′ by 3′ and that it’s at least three feet high when first assembled.

Oxygen: If it’s a new pile, the problem isn’t likely to be a lack of oxygen unless you packed the pile down and ran your tractor over it. The exception would be if it contains large clumps or layers of material like leaves, sawdust or grass clippings that tend to form dense mats. Dead leaves compost slowly under any conditions because they’re so high in carbon. If they’re not mixed with other ingredients, they’ll compress into a nearly oxygen-free lump. So will grass clippings, which will quickly go anaerobic, turning slimy and stinky. In both cases, it’s best to turn the pile, mixing these ingredients in with others. When adding new materials, don’t leave them in a clump but mix them in throughout the pile. Using leaves? Shred them.

Moisture: If you don’t have big clumps of leaves or grass in your pile, then exploratory surgery is necessary. Get out a pair of gardening gloves and dig into the pile a ways in several places. Does it seem damp? If not, add water. Actually stick the hose into the pile — again, in several places, not just one — and let it run for thirty seconds or so, then sprinkle the top liberally.

Check it each day for a while to be sure you’ve added enough.

Too much moisture can also put a damper on hot composting. But this isn’t very likely with a newly built pile. New piles usually contain plenty of air pockets and their ingredients don’t absorb water nearly as well as does finish compost or even partly composted material. If you think this might be the problem, check the solution below under “Old, Maintained Piles.”

Nitrogen: If the pile still doesn’t heat up in the next three to four days, you’ve probably got a nitrogen deficiency and this, unfortunately, may mean that you’ll need to rebuild the pile, incorporating a high-nitrogen material throughout. An alternative would be to sprinkle such a substance — blood meal, organic cottonseed meal, kelp, or manure — on the pile and water it in. It won’t distribute evenly, but it should help. And when you turn the pile the booster will get mixed throughout.

Micro-Organisms: If you know you added plenty of green stuff — for instance, the pile is a quarter grass clippings and they’re well dispersed, not concentrated — then you’re down to the last possibility: not enough micro-organisms. This is a rare and usually self-correcting problem, but one circumstance does make it more likely. If you isolate the pile from the ground, the microbes that live in the earth have no way up into your heap. Occasionally someone will have the bright idea of building a compost pile on a sheet of plastic, often with the aim of making distribution easier, sometimes with the goal of collecting the leachate — the liquid that seeps out. It’s a great idea as far as it goes, but it cuts the pile off from its primary source of micro-organisms: the dirt beneath it.

Once you’ve eliminated all other possible causes of a slow-starting pile, try boosting the population of micro-organisms. This can be done by adding some fresh finished compost, which should be rich in microbes. For quick results, buy an inoculant which is actually the micro-organisms themselves, dry but almost undiluted. Ordinary dirt contains composting bacteria. Adding some will introduce the organisms, but not as effectively as adding compost or inoculant. (There’s some disagreement in the composting world about the value of dirt in a compost pile; finished compost. if you have it, is a better choice.)

In all cases, turning the pile and mixing in the new microbe source gets the best results. In a pinch, sprinkle it on top and water thoroughly. And plan ahead for future batches: add microorganisms, finished (but fresh) compost, or thin layers of soil to your piles as you’re building them to ensure that they’ve got adequate supplies of the bacteria that do the composting job.

Problem Symptom Solution To Avoid in Future
Lack of moisture Feels looks dry Add water Water pile as it’s being built, after every two to four inches of new material.
Lack of oxygen Matted ingredients; large quantities of leaves, sawdust, or grass added in clumps Add oxygen: Turn pile or fluff. Mix ingredients well when building, esp. those that tend to mat.
Lack of nitrogen The pile doesn’t heat up; slow decay Add high-nitrogen material: blood meal, organic cottonseed meal, corn gluten meal. Sprinkle high-nitrogen material over every 2-4 inches of new material as pile accumulates.
Lack of microorganisms None of the other factors apply; pile still doesn’t heat up. Add micro-

organisms directly (inoculant) or indirectly (fresh compost, soil).

Don’t build piles on plastic sheets; don’t isolate piles from the ground; save some fresh compost from finished pile to incorporate into new pile; add micro-organisms to new piles.
Old, Maintained Piles

This is a pile that was built to get hot and maybe did so once, but now it’s cold and unfinished. Most of the possible causes that apply to Newly Built Piles (above), still apply here.

Oxygen: With piles that have only heated up once or twice, start by turning the pile to introduce new oxygen. If this gets no results, then check the moisture level and add water if necessary. A lot of piles stall out because they dry out.

Moisture: New piles are seldom so wet that moisture impedes microbial activity. Older piles, especially ones left open to the weather in a rainy season, may develop problems from too much moisture. Water can fill the gaps and spaces inside your pile, driving out the oxygen aerobic bacteria need.

Turn the pile, incorporating plenty of hay, dry leaves or other dry, absorbent material as you do. Be aware, though, that all of these materials add far more carbon than nitrogen so you might need to add a nitrogen source to keep the C/N balance. If you don’t have any dry ingredients that fit the bill, you might have to spread the compost out to dry.

To prevent this problem from recurring, fashion some sort of lid for your compost pile, even if it’s only a tarp during rainy weather.

Microbes: One problem that’s unlikely to afflict an older pile is a lack of microbes. If a pile has heated up even once, it’s got plenty of microbes in it. The population doesn’t die off. But it never hurts to add finished compost to a cold pile, if only to encourage the microbes already there.

Nitrogen: This one is unlikely. A pile that has enough nitrogen to get truly hot once usually has enough to last out the entire composting process. But there may be the occasional exception. If it’s heated up once or twice but won’t heat up after turning and it’s neither too dry nor too wet, then try turning it again. Introduce nitrogen throughout as you turn.

The most cheerful addition to the list is the possibility that the compost is done. If it’s performed like a champion for several weeks or months, heating up whenever you turn it, but now the temperature doesn’t budge even when you fork it over, then this is most likely the answer. If it looks, smells, and feels like soil or compost, then it’s done. Screen whatever remaining materials, twigs and the like, out of it before using. Though it can be used at once, it’s best left to cure for a week or two.


How can this be a problem? By killing off the very reason that compost is so effective; the beneficial microbes. At temperatures above 160°F (71°C) or so, beneficial micro-organisms begin to die off. Adding this compost to your soil will quite simply not be as beneficial as it would be otherwise. In fact, the extension service at the University of Illinois warns that at temperatures this high, “the composting material may become sterile and lose its disease-fighting properties.” Those properties, after all, come to us courtesy of bacteria. Kill the bacteria and you kill off any chance for antibiotic action as well.

Unless you have a thermometer in the pile, you probably won’t know if it heats up over 140°F (60°C). It’s next to impossible to tell by hand the difference between 140°, which is optimal, and 160°F (71°C), which is getting close to a temperature that will kill off beneficial organisms. A compost thermometer is a good investment.

Commercial and municipal composting systems actually aim for these very high temperatures to ensure that pathogens are killed off, but they’re not practical for the home composter. Assuming that your pile is free of pet and human feces or other sources of human pathogens, it’s best to keep composting temperatures below 155°F (68°C).


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