"Your #1 source for information about how to compost."
HOW TO COMPOST
What a Good Pile Needs
What You Need
Extras & Additives
What to Use - or Not!
Building the Pile
When is it Finished?
Just Do It
More Than Just Dirt
Water & Soil Remediation
A Few Concerns
What You Can Do
OdorsIf a compost pile smells, something is wrong. Ordinary composting does not smell. This may be a surprise, as we think of rotting as a smelly business, but there it is. Only two sorts of smells usually afflict a pile, and since these have clear and distinct causes, they're actually quite easy to diagnose and to treat.
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. (It's also unpleasant since it requires that you be in close quarters with the offensive pile, but that's life.) Rebuilding it on a palette will help keep air flowing through it as will incorporating some large sticks in the middle. If the pile keeps reverting to an anaerobic mode it's time to explore a different composting style. A method such as sheet composting, for instance, doesn't let material build up enough to smell, and trench composting gets it underground immediately. See more on these and other options in the section on How To Build A Compost Pile.
When a compost pile smells like ammonia, it is giving off excess nitrogen (N) in the form of ammonia (NH3). There's no clearer signal that it has too much nitrogen in it. This problem occurs most often if a composter has been adding high-nitrogen products.
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 add less nitrogen in future.
The Pile Won't Heat UpYou hear about how compost piles heat up but yours never does. Why? Is the hot pile a myth? No. Chances are your pile simply doesn't have what it takes. Supply what's needed and it will take off.
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 piles that get new stuff added to them continually over the year will not heat up. There may not be enough nitrogen and it's almost certain that the oxygen supply at the bottom has been depleted. Even if the nitrogen and moisture balance in the new material is perfect there's probably not enough of it to support the population of microbes that would 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. The second, turning, will ensure that the hot composting process reaches all the old material as well as the new.
Simply turning the pile may be 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 just sit there being cool. 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. 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.
As all this makes clear, converting a cool pile to a hot one will take 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. If you have a thermometer in it, 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. So 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 settle 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 and taking away with you the lesson to next time mix them when building the pile.
Moisture: If you know you don't have big clumps of leaves or grass, then exploratory surgery seems called for. So 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 finished 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 -- the pile is a quarter grass clippings, for instance and they're sprinkled, not concentrated -- then you're down to the last possibility, a paucity of micro-organisms. This is a rare and usually self-correcting problem, but one circumstance does make it more likely: isolating the compost pile from the dirt beneath it. Occasionally someone will have the bright idea of building a compost pile on a sheet of plastic, usually with the aim 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.
At any rate, if 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 relevant bacteria. For the very quickest results, buy an inoculant which is actually the micro-organisms themselves, dry but almost undiluted. Since ordinary dirt also contains composting bacteria, you can also use this though the results won't be nearly as swift. (There's some disagreement in the composting world about the value of dirt in a compost pile.)
In all cases, turning the pile and adding the new ingredient throughout gets the best results. In a pinch, sprinkle it on top and water thoroughly. And make a note for future batches: add micro-organisms, 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.
Old, Maintained Piles
This is a pile that was built to get hot and that did so at least once, but now it's cold. Most of the possible causes that apply to Newly Built Piles (above), still apply here, plus or minus one or two.
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: While it's unlikely for a new pile to be so wet that moisture impedes microbial activity, this is a distinct possibility with older piles, especially ones left open to the weather in a rainy season.
The aerobic bacteria that cause a pile to heat up need atmospheric oxygen. If all the little gaps and spaces in the pile are full of water, there's no space for air.
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 and you'd have to work extremely hard to kill them all off. So this is one you can cross off the list.
Nitrogen: This one is unlikely but not impossible. 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 two wet, then try turning it again while introducing nitrogen throughout.
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 look, smells and feels like soil or compost, not like bits of last year's garbage, then it's done. Though it can be used at once, it's best left to cure for a week or two.
OverheatingThe problem with this problem is that you may never know you have it. That sounds like an advantage. Unfortunately, though the symptoms may escape you, the effects will be real. At temperatures above 160°F (71°C) or so, beneficial micro-organisms and 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 antibiotics as well.
Unless you have a thermometer in the pile, you probably won't know if it heats up over 140°F (60°C). (Can you really tell the difference between 140°, which is optimal, and 160°F (71°C), which is getting close to a temperature which will kill off beneficial organisms? Probably not.)
Commercial and municipal composting systems actually aim for these very high temperatures to ensure that pathogens are killed off, but they're not ideal 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).
"I Need It Now!"Most gardeners have run into a compost crisis: a realization that the pile on hand is just not going to produce what's needed fast enough, and one will either have to go without or -- horrors -- purchase commercial compost. Sometimes -- not always -- it's possible to hurry a pile along.
First, the "not always" conditions. A hot pile already operating at maximum capacity cannot be sped up. If the compost thermometer reads 150°F (65.5°C), raising the temperature risks killing off many of the organisms that make compost valuable. Secondly, if you need your finished compost tomorrow or even next week, you're out of luck; it's time to hit the gardening center. Third, if your pile is completely saturated with water, it's probably not possible to both dry it out and compost it within the time available. Finally, if you don't have enough material on hand for at least a 3' by 3' pile, there's not much you can do.
However, if you've got a partially composted pile of reasonable dimensions and three weeks (or six) to work with, then many things are possible. The further along your pile already is and the more material you've got to work with (within reason) the better. Specifically, a cool continuous pile can be converted into a hot batch pile.
For emergency actions, it's a good idea to have on hand a couple of compost boosters such as a nitrogen source and a compost additive to add additional microbes. A pair of gloves, always a good idea when handling immature compost, will be especially welcome in the following exercise as some of the ingredients are sure to be slimy.
The basic plan here is to haul everything out of the bin and rebuild the feedstock into the hottest pile on the block. Even if you don't usually chop up ingredients, this would be the time to do so. A hoe, turf edger or sharp-edged shovel can accomplish a great deal though a pair of clippers might come in handy as well. Anything that resists even this level of treatment should be removed; put it in a different, less urgent pile.
On the other hand, new material that's high in nitrogen and quick to decompose should be welcomed. This includes fresh leaves and grass trimmings as well as soft kitchen waste: plums, peaches or potatoes past their prime, but not carrot ends, peanut shells or cantaloupe peels.
Before you return material to the bin, create an open airspace at the bottom by laying down sticks, a wood pallet, or even a layer of wood chips or pine cones. This will allow continuous aeration from below which will reduce the need for turning.
After you've pulled everything out, chopped as much as you can, and added new material, rake it all together and mix it up with a garden fork or pitch fork. Bunches of leaves or matted grass need to be shaken up and mixed with other things. Use dirt if nothing else comes to hand. If you're working on a tarp, you can sprinkle the feedstock with some of the nitrogen and dry activators as you work.
When the material is well mixed, put down a six-inch layer in the bin and sprinkle it with nitrogen and microbes unless, of course, you've already added all the boosters that the directions recommend. Also sprinkle with water if needed, remembering that feedstock should be damp, not wet. Repeat until the bin is full. Sprinkle the top with boosters and with an inch or two of soil or mature compost or several inches of hay.
Poke holes in the pile with a piece of rebar -- lots of holes, spacing them three to six inches apart. If they're not there the next day, do it again. These holes provide aeration channels, drawing air up from the bottom of the pile.
If your bin doesn't have a lid, figure out some way to protect the compost from rain. Rain will cool the pile down; it will also saturate it, which slows or halts aerobic activity. A folded tarp can act as a lid of sorts, as can a tarp that's held away from the sides of the bin so that it doesn't impede air circulation.
A pile given this kind of kick-start will get very hot, and it will get hot fast. In fact, the biggest danger is that it will overheat, killing off beneficial organisms. It's a good idea to work with a thermometer to guard against overheating. If the temperature starts to rise too high, poke holes in the pile with a piece of rebar or pull off the top foot of material and then replace it.
To keep the pile cooking at maximum speed, turn it as soon as the temperature drops to about a hundred degrees. This is only a few degrees warmer than your body, so the inside of a pile at this temperature will feel only slightly warm. Keep turning it every time it cools down. It's fine to turn it a little sooner -- at about 110°, for instance -- but above that you're creating more problems than you're solving.
Fruit Flies & Fungus GnatsMost piles have a few fruit flies and fungus gnats; if they don't bother you, they're not hurting the pile. Fungus gnats can actually damage plants where the compost is applied so it's a good idea to eradicate or at least deplete them.
The best way to figure out what you've got is to put a bit of the finished compost in a pot and bring it indoors where you can observe it. Putting it in a plastic bag or under a plastic cover ensures that you're not just moving the problem indoors. Fruit flies are paler and rounder than gnats which tend to be slender, shiny, and almost black. Gnats, unlike flies, will often run away, rather than fly away, when startled. They spend a lot of time crawling around on the surface of the dirt and on the outside of the pot and they're frequently to be found tucked under the bottom.
Some control measures work equally well for both species; those that don't are described separately below under Gnats.
• Both fruit flies and gnats feed on damp, decaying organic matter, preferably fruits, so bury all fruits and vegetables deep in the pile. Don't just dump them on top where the flies can easily find them.
• Better yet, wrap kitchen waste in a sheet of newspaper and then bury it deeply. This adds an obstacle between the flies and the garbage.
• Check the moisture level in the pile. Both gnats and flies need a damp environment; their presence sometimes indicates a pile that's gotten too wet. If that's the case, turn it frequently to aerate it and add dry leaves or straw.
• Set traps on the surface of the pile. One trap for fruit flies is described in trouble-shooting in the page on Vermicomposting. Another consists of a jar with liquid bait at the bottom and a funnel fitted into it upside down, so that the narrow end of the funnel points down. The insects get funneled downwards towards the bait, but very few can find their way out again. Numerous versions of this trap exist; one recommends cutting off the top of a soda bottle and inverting it, so that the neck of the bottle points downwards. In another version, the funnel is made of paper, taped to the side of a glass jar. Some are baited with vinegar, some with apple-cider vinegar; one uses apple-cider vinegar with a drop of dish soap. Red wine would also work well. Only half an inch of liquid should be necessary. Set several of these around the top of the compost pile.
• Switch to a hot system and chop all ingredients when setting it up. This destroys many larvae and pupae on the feedstock and creates an environment less friendly for breeding.
GnatsGnats in the finished compost require action. If they're not eradicated, they'll travel with the compost to every pot or plot it reaches. The larvae eat organic matter, including the root hairs of plants, causing real damage if the infestation is serious enough. Inside, the adults can be intensely irritating.
Beneficial nematodes in soil feed on gnat larvae so infestations can be controlled by inoculating soil or compost with these nematodes. This method works well but it's not instantaneous: the nematodes get added to the top layer of soil, often with coir to ensure they don't dry out. It takes them a while to proliferate and to gain the upper hand in soil or compost that's already infested.
It's best to put the infested medium in bins or in garden pots in the garage or some out-of-the-way spot, add the nematodes as directed, and give them several weeks to proliferate before using the compost, especially if you're bringing the pots indoors. Don't let the pots dry out or freeze while the inoculation is underway as this may kill off the nematodes. A U. C. Davis site on controlling various gnats and flies says that "Beneficial nematodes can provide relatively long-term control of fungus gnat larvae and they can be self-reproducing after several initial applications to establish their populations." In other words, it might be necessary to apply them more than once.
A predatory mite, Hypoaspsis miles, can be used in a similar way with similar results.
The biological insecticide, Bacillus thuringiensis israelensis, is also effective against fungus gnats. Along with nematodes, this is the top gnat control recommended by U. C. Davis: "If insecticides are required for fungus gnats, consider using Bacillus thuringiensis subsp. israelensis or Steinernema feltiae nematodes to control the larvae...." Bti is a particular strain of Bt, all strains of which are derived from naturally occurring soil bacterium. They are remarkable because they are harmless to plants, humans, animals, fish, earthworms and beneficial insects such as ladybugs and lacewings.
Widely available as powders and sprays, it is the more recently developed Mosquito Dunks that some composters have discovered. The donut-shaped dunks, whose active ingredient is Bti, are designed to be used in standing water, so these innovative composters soak one in a pail and pour the water over the compost pile. Some composters use prepared water whenever they build a pile to help control gnats.