Some compost methods are fast enough to produce finished compost is 14 days or less. Other more risky compost methods can take up to 2 years before finished compost can be harvested. The amount of time compost takes to complete depends on several factors.
Factor 1: Compost Method
On our sidebar you will see a list under the heading “Composting Methods.” Each of these methods has its own subtleties that can greatly affect the speed of compost production. For example, the Berkeley method was developed to maximize the speed of composting by grinding all the inputs into powder and turning the pile daily, maximizing surface area and oxygen to produce compost in 11 days rather than the average 3-6 months. Most households need not be concerned with this breakneck speed, and can opt for a much slower, cold composting process. A compost producer who wishes to have compost sooner than with the cold composting method yet doesn’t wish to purchase the machinery necessary for the Berkeley method could opt for the mid-scale batch composting method.
Factor 2: Carbon Source
I have found that building a compost with wood chips makes a compost finish much faster than a compost built with leaves. Part of the reason for this seems to be that a pile built with wood chips can dry out very easily, causing any nitrogen source to vaporize into the air rather than being preserved in the finished compost. If a fertile compost is your goal, it is better to limit your use of wood chips for this reason, even if the compost will not finish as quickly.
Factor 3: Texture of Materials
Texture is a very important consideration in composting. The best texture is one that has has a high surface area while still allowing plenty of air into the middle of the pile. Straw is a good example of a material with lots of surface area, yet enough structure to build a pile with lots of air passages. Leaves tends to mat and do not provide good airflow, and wood chips tend to not have enough surface area for the amount of carbon they contain. Mixing different materials together is often an effective way to mitigate some of the downsides of some materials.
Right: Straw has the best texture for compost, but usually costs at least 4$ per bale. If you want to build your compost with straw, try to secure a source for moldy straw or used stable bedding straw.
Factor 4: Frequency of Turning
Turning a compost pile often greatly increases composting speed by oxygenating the compost micro-organisms. Each complete compost turn seems to cut the remaining compost time in half. For example, if you have one cubic meter of half-finished compost with an estimated finishing time of 3 months, you could hasten the finishing time to one and one half months by flipping it today. The Berkely method has the most aggressive turning regimen of one full turn each day.
Factor 5: Moisture of Pile
The overall moisture of a compost pile needs to be within a “goldilocks” zone, not too dry and not too wet. Too much moisture in a pile can slow the composting process by reducing the heat. A wet compost pile is also more likely to undergo anaerobic digestion, leading to a smelly, wet, unpleasant sludge.
Conversely, not enough moisture will dry our the habitat of your micro-organisms, leading to an overall slower decomposition process. If the pile gets too dry, your “greens” will start to turn into “browns” and you will eventually end up with a dried-out pile with a higher than optimal ratio of carbon to nitrogen.
Factor 6: Ambient Temperature
Like grizzly bears, compost micro-organisms like to hibernate during the winter! A pile that will finish in under 2 months in summertime can take 4 to 6 months to finish in the colder months! However, by building large piles and insulating with straw or leaves, you should be able to maintain higher internal temperatures throughout the winter despite the cold.
Factor 7: Internal Temperature
A properly built hot compost pile can reach 160°F, significantly higher than the recommended temperature of a home water boiler. The heat of a pile is an indication of biological activity of a compost ecology, meaning that hotter compost piles break down much faster than a cold compost method.
Factor 8: Risk Factors
One reason composting is such a great process is that some bio-hazards can be rendered inert, even useful, by composting them. For example, you could replace a septic field or sewer system with a “humanure” compost system, turning a waste product into a useful input. In the humanure example however, compost should be allowed to cure for at least one year before the finished compost is used on any edible crops. Composting these risky materials obviously significantly increases your compost time.