Problems in compost piles are relative. The occasional bad odor in a passive pile behind the barn in a rural area may not be considered a problem, whereas the same situation in a dense urban neighborhood may bring the police to your door. The problems addressed here are offered with the understanding that, for some home composters, they may not be serious or require any action.
Eliminating Unpleasant Odor
Bad odor is perhaps the most common problem identified by home composters. No matter the cause, the odor will disappear quickly if you turn the pile and add carbon-rich material.
To avoid a recurrence of odor, understand that unpleasant smells usually develop because the pile has become anaerobic—it has no air. This may occur when the pile is compacted or when it’s soaked with moisture. Turning the pile restores air. Additionally, an anaerobic pile often contains an excess of nitrogen-rich material. Guard against putting too much fresh green material in the pile without adding sufficient carbon-rich material. Also, if heavy rains are likely, cover the pile.
Without adequate moisture, microorganisms cease functioning and decomposition comes to a halt. A sign of this problem is lack of settling. A properly moistened pile shrinks by at least 30 percent in just a month or two. If this doesn’t happen, assume your pile isn’t moist enough. The best solution is to turn the heap, applying water with a garden hose as you restack the pile. If you don’t want to go to the trouble of turning the pile, however, you can still moisten the pile well enough to spur decomposition.
Just pouring water on top of an established pile won’t wet the center, because the water will sluice off the outer surfaces. It takes a long soak for water to work its way to the bottom of a pile. Either turn the garden hose on to a drip and let the water seep into the pile in various locations, or scoop out a shallow hole in the top of the pile to trap the water. The trapped water will eventually work into the heap. Keep the cover off for one or two soaking rains. If there is no rain, add water with a garden hose once or twice more.
The only cure for an overly wet pile, no matter the cause, is to turn the pile while adding dry carbon-rich material. The yellow material helps absorb the excess moisture and keeps the pile from putrefying. If you do nothing, the wet pile may start to smell. And, since it lacks air, the material will take at least a year to decompose.
Except during cold weather, the center of a compost pile should be uncomfortably warm or even hot to the touch. A new pile should heat up within a few days, get hotter for a couple of weeks, then slowly cool as it uses up its air. If the pile went through this cycle, it only needs turning to aerate it, and it will heat up again.
If the pile never heated up, or only heated a little bit, check to see if it’s dry. Decomposition slows down in a pile that’s either too dry or too wet (the preceding paragraphs present solutions for both problems).
If the moisture level is correct, the most likely cause for the lack of heat is that the pile is too small. Unless the pile is at least 3 by 3 by 3 feet, it doesn’t have enough critical mass to hold the heat generated by the microbes.
If the pile is adequately moist and large enough, the problem may be a deficiency of nitrogen-rich material. Add fresh, green material or high-nitrogen fertilizer and turn the pile.
Most composting microorganisms become inactive below 40 degrees, although psychrophilic bacteria work in temperatures as low as 28 degrees. Decomposition continues at a slow rate even in colder weather, since the interior of a compost pile is always warmer than the air temperature. However, a moist pile that isn’t covered can freeze during a cold winter. Logic seems to indicate that turning the pile would spur microbial activity and heat up the compost material, but doing so will actually accelerate the heat loss. Keep the pile warm by covering it with clear plastic, which serves as a solar heating mechanism. If the pile freezes despite covering, don’t worry; the decomposition process will resume in spring.
Houseflies and fruit flies around the compost pile indicate that the pile isn’t properly built or maintained. Rather than dealing with them once they become a problem, prevent the pests by using correct techniques from the start. Unless you treat food waste properly, it’ll attract flies. The same is true of fresh manure. Whenever you add either to the pile, cover it with carbon-rich material, soil, or old compost. A tarp or other covering over the whole pile isn’t a substitute and won’t keep out flies.
If the flies have already arrived and maggots are present, turning the pile won’t eliminate them because the maggots will migrate to the cool exterior of the pile. Spraying the maggots with a pesticide is only partially effective because they are burrowing in the pile and difficult to wet.
One solution is to seal the pile in plastic. Tape the seams and seal the bottom by piling soil on the edges. This will keep any flies from escaping, and the resulting anaerobic conditions will eventually kill the maggots.
Precluding Animal Pests
Sometimes, home composters have problems with cats, dogs, opossums, raccoons, and even rats around the compost pile. Here again, preventing these pests is preferable to coping with them after they arrive.
None of these animals will be a problem if the pile is built and maintained properly. Animals whose habitats are nearby may not even be aware of the pile if you take the basic precautions: add a layer of carbon-rich material, soil, or old compost over food waste. The topping keeps the pile from smelling and attracting animals.
If animal pests are a particular problem in your area, choose a bin that denies access to the creatures.