Three factors are usually to blame: poor aeration, too much moisture, or not enough nitrogen-rich material in the pile. A compost pile overburdened with materials that mat down when wet—grass clippings, spoiled hay, heaps of unshredded tree leaves—can become so dense that the pile's center receives no air.
Decomposition will be complete anywhere from two weeks to two years depending on the materials used, the size of the pile, and how often it is turned.
The Pile Has an Unusual Smell
Generally, the scent of compost should be earthy and green. An intensely moldy or musty smell is a sign that something is amiss. If compost begins to reek of rot and putrid odors, there is likely too much material entering the pile before it has the chance to break down.
Compost is ready or finished when it looks, feels and smells like rich, dark earth rather than rotting vegetables. In other words, it should be dark brown, crumbly and smell like earth. The Florida Online Composting Center is one of the few sites that offers detailed home tests for the maturity of compost.
Solution: Bring air into the pile by turning it over regularly or use a pitch fork to “fluff it up” every few weeks. You can also use a rotating compost tumbler to keep things aerated with little effort (Read more in our article, Compost Tumblers vs. Compost Bins.)
Turning your compost too often or not enough
Stirring or mixing the compost pile helps the decomposition process by adding oxygen. “A lot of the microbes in a compost pile are aerobic, meaning they need at least some air, [which] allows them to multiply, to breathe and to break down your compost faster,” says Guiliano.
If your pile is slow, the carbon: nitrogen ratio might be wrong. The microorganisms in compost need both nitrogen and carbon to work. If there is too much carbon, the process will slow down. To speed up the process try adding 'greens' – items that are high in nitrogen, such as grass clippings or manure.
Nutrients will leach out of compost over time. This depends on different factors, such as how it is stored. In general, the older the compost, the fewer nutrients it offers. Compost contains nutrients like nitrogen, phosphorus, and potassium, but only small amounts.
What is this? You can, and you probably should include a small amount of soil in your compost. It can help speed up the composting process and also prevent common composting problems like odors or insects.
Some other composting problems can get in the way of the process, including: Foul smells, which may indicate your pile is too wet or has too much nitrogen. Attracting rodents and animals, which can indicate an issue with what you're adding to the pile.
Compost that is too wet will smell putrid or like rotting eggs and will look slimy, especially green material.
The passive composting methods are also known as cold composting, and you need to stop adding to the pile around when it should be done decomposing, which can take up to two years. In batch method composting – or hot composting – you need to stop adding to the pile until it has heated up and cooled entirely down.
Turning once a week or once every two weeks had generally lower decomposition rates. To maintain a thermophilic pile (pile with high heat), it should be turned every three to four days, or when the temperature drops below 104 F. However, if most of the material has been decomposed, less frequent turning is adequate.
The rule of thumb for an active, hot pile is every three days until it stops heating up. Some over-enthusiastic composters rush out after a day and turn the pile. This is a bit too much of a good thing.
Composting works in sun or shade Piles in sunny spots will decompose quicker but also dry out faster and may need supplemental watering during hot dry weather. Those located in a shadier spot will stay moist longer but decompose slower. In either case, make sure the soil below the pile is well-drained.
Question: Do I have to turn my compost? Answer: Kitchen and yard waste will compost even if you do not turn it. Microbes, bugs and worms will do the work. No one turns a forest floor where even the fallen trees will compost just fine.
You may be surprised to learn that your compost pile needs just as much water as your live plants. Dry compost doesn't work. There are several ways to ensure your compost is getting the adequate amount of water needed to do its job.
The quick answer is that in general, worms can help speed the composting process that turns scraps and debris into usable garden conditioner. Some types of worms consume and digest rotting vegetables and other matter you put into the bin. They excrete material in a form your plants can use as nutrients.