Now that you are familiar with the pros and cons of hot composting, are you eager to get started? Or do you feel 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
You can easily start a cold compost pile with whatever materials are on hand. A precise balance of “greens” (organic matter high in nitrogen) and “browns” (organic matter high in carbon) is not necessary for success. However, incorporating both into the pile will help the decomposition process go faster. Likewise, you can chop up large pieces of material, such as sticks, for faster composting, but this is not necessary. You can build the pile gradually.
As with hot composting, air is a requirement to avoid the accumulation of smelly anaerobic bacteria. 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, turn the pile or drive air holes into the center with a stake or piece of rebar.
As decomposition progresses, you may want to monitor the moisture content. If persistent rains are a problem, consider covering the pile 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 nearly perfect to make it happen. You may appreciate the ease with which you can build and maintain a cold compost pile.
- 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? Dig out the finished compost underneath to use immediately.
- Fewer material requirements. With hot composting, you need at least three cubic feet of organic matter ready to go at once. With cold composting, you can add materials little by little as you accumulate them.
- 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 will help mechanically break down materials.
- Minimal turning. 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.
- 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.
- Space requirements. A cold compost pile takes up space for months at a time. Find a corner of the garden that is out of the way, but not too far from the beds to be convenient. (Also keep in mind that the compost pile may not be the prettiest thing to see out your kitchen window.)
- Slow going. Even with frequent turning, cold composting takes about six months to a year—sometimes longer. If you need compost fast, you definitely need to consider hot composting.
- Anaerobic decomposition risk. 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. Unless aerated from time to time, 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.
- 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.
- Persistence of undesirables. Heat is necessary to break down pathogens, weed seeds, and chemical residues. Never use the cold composting method to process diseased plant materials, invasive weeds, weeds that have gone to seed, or debris from lawns, gardens, or farms treated with herbicide or other chemicals.
- Nutrient leaching. Depending on how long the composting process takes, nutrients can leach out of the pile with every rainfall. Using a composting container or covering the pile with a tarp in wet weather will help preserve valuable nutrients. 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 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. Furthermore, it 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.