Now that you are familiar with the pros and cons of hot composting, are you eager to get started? Or are you overwhelmed just thinking about all that preparation and turning?
If you fall into the latter category, don’t give up on composting altogether just yet. First consider cold composting.
Introduction to Cold Composting
A cold compost pile can be started with whatever materials are on hand. The pile can be built gradually over time.
While a precise balance of “greens” (organic matter high in nitrogen) and “browns” (organic matter high in carbon) is not needed for success, incorporating both into the pile will help the decomposition process go faster. Likewise, large pieces of material, such as sticks, can be chopped for faster composting, but this is not necessary.
As with hot composting, air is a requirement to avoid the accumulation of smelly anaerobic bacteria. Air can be introduced by periodic turning, but again this is not essential. One way to allow air circulation within the pile is to pay attention to how ingredients are layered. For example, some coarse (but not too long) sticks in the center will help. Also, soggy materials that stick together like fresh grass clippings or wet leaves should be allowed to dry slightly before going into the pile. If for any reason air flow becomes a problem during the composting process, air holes can be driven into the pile with a stake or piece of rebar.
As decomposition progresses, the moisture content should be monitored. If persistent rains are a problem, the pile should be covered with a tarp to avoid drowning and subsequent anaerobic decay. In dry weather, a periodic sprinkling with a hose will be beneficial.
Cold composting goes very slowly. How slowly depends on the size of the ingredients, the ratio of greens to browns, and the frequency with which the pile is turned. These variables also affect the temperature that the pile will reach. A maintenance-free cold pile may never even hit 90°F. Piles that contain green material and are turned periodically may get somewhat warmer.
The bottom of the compost pile decays first, usually leaving large pieces of high-carbon material intact on top.
- Simplicity. Getting a compost pile to heat up is not easy. Conditions have to be just about perfect to make it happen. If gardening is not your full-time job, you may appreciate the ease with which a cold compost pile can be built and maintained.
- Flexibility. One of the biggest advantages of cold composting is that it can be adapted to your needs. Don’t have much to compost? Just toss on what you do have and wait for another opportunity. Don’t have time to turn the pile today? It’ll wait until tomorrow, or next week, or next month. Ready to cut the process short? Throw away the larger uncomposted pieces of material and dig out the finished compost underneath to use immediately.
- Fewer material requirements. With hot composting, you need three, four, or five cubic feet of organic matter (properly balanced between greens and browns) ready to go at once. With cold composting, you can add materials as you accumulate them. One day, you can add the grass clippings. A few days later, you can throw a banana peel on top.
- Compost year-round. Many gardeners become frustrated after trying to get a compost pile to heat up in cool weather. With cold composting, you can let the decomposition process continue all year. Even in January, freeze-thaw cycles and periodic introduction of moisture in the form of snow will help mechanically break down materials, long before the microbes awake from their winter slumber.
- Minimal turning. Let’s face it. Not every gardener can find time to turn a bulky compost pile every few days. With cold composting, you can simply turn the pile whenever you have a spare half hour or so. Or you can let it go from start to finish without ever picking up a shovel. This also makes cold composting a great option for an older gardener who wants to garden naturally but finds hot composting back-breaking.
- Nature’s way. Where in nature have you seen a hot compost pile steaming away, with obliging creatures turning it at just the right time? Probably nowhere. Nature makes compost slowly.
- Beneficial organisms. Many microscopic forms of life can survive in the lower temperatures of a cold compost pile. This includes beneficial fungi and bacteria that thrive on moderate temperatures. These are exactly the microorganisms that your plants need to stay healthy and fight disease. Some gardeners speculate that the preponderance of fungi in cold compost is just right for raising trees.
- The ugly factor. As much as natural gardeners love good soil, a half-rotted compost pile may not be something they want to see out their kitchen window every day. While a hot compost pile can do its work and be hauled away in a matter of a few weeks, a cold pile will likely be sitting in the same place decaying all summer long. Choose your location accordingly.
- Space requirements. A cold compost pile will be taking up space for many months at a time. When choosing a place to build a pile, find a corner of the garden that is out of the way, but not too far from the beds to be convenient.
- Slow going. Cold composting takes about six months to a year—sometimes longer. While you can speed up the process by adding ingredients faster or by turning the pile more frequently, if you need compost fast, you definitely need to consider hot composting.
- Anaerobic decomposition. Cold piles can collapse over time and loose their ability to circulate air, especially if they contain things that tend to stick together like wet grass or leaves. A smelly bacterial mess that draws flies can be the result. With a hot pile, the frequent turning is sufficient to introduce air into the center of the pile. Cold compost piles should be aerated from time to time; of course, this means they are not exactly maintenance-free.
- Pest attraction. Bugs and mammals love cold compost piles. Chances are, you are going to see a lot of flies and rodents. Fencing can help keep larger pests, such as raccoons and stray dogs, away.
- Chemical persistence. Heat is necessary to break down any chemical residue, such as pesticides and herbicides, remaining on compost ingredients. If you use chemicals on your lawn, do not add the grass clippings to a cold compost pile.
- Weed survival. Weed seeds will make it through the low temperatures of cold composting intact, guaranteed. If you composted pulled weeds, you can expect them to put in a second appearance after you apply the compost. For best results, never compost invasive weeds, or noninvasive weeds that have gone to seed.
- Disease survival. Most diseases can also survive the cold composting process. If you will not be maintaining a hot pile, you should definitely avoid any diseased plant material. Either ship diseased plants out with your trash, or burn them.
- Nutrient leaching. Depending on how long the composting process is drawn out and on the weather conditions at the time, nutrients can leach out of the pile with every rainfall. Using a composting container will help contain all the valuable nutrients your plants need. Covering the pile with a tarp in wet weather is another possibility. Also, you can periodically dig out the finished compost from the bottom of the pile to use immediately.
- Uneven decomposition. Remember, the compost will decay from the bottom up. While you’re waiting and waiting for the organic matter on top of the pile to break down, there is good compost that you could be using accumulating underneath. Even when finished, there will likely be large particles remaining, resulting in a coarser final product than is achieved with hot composting.
The reason that busy gardeners often choose cold composting should be obvious by now—a cold pile can be as low-maintenance as desired.
While this is an important consideration, there is another factor that should be given some thought, and this is the quality of the finished product. Cold composting is definitely a more natural method than hot composting, and it definitely fosters more of the beneficial organisms necessary for plant health. Under optimal conditions (i.e., if not dragged out too long or flooded by repeated rainfalls), it may even contain more nutrients.
However, there are certain circumstances under which cold compost will be of doubtful quality. If any of the ingredients contain chemicals, disease organisms, or weed seeds, these contaminants will be perpetuated in the compost. Therefore, gardeners who have doubts about the ingredients should either discard them or use the hot composting method.
Finally, time is also a factor. For those who don’t mind waiting several months for finished compost, cold composting is a viable option. Gardeners who need to build and amend the soil quickly will benefit from the hot method.
Composting Quick Start
Everything you need to know about composting, including a step-by-step guide to the cold composting method.
The Complete Compost Gardening Guide
This book may convince you to give slower methods a try. It also provides step-by-step directions for many different methods of cold composting. Read our full review.