Category: The Garden

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 in 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 just 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 materials intact on top.

 

Pros

• 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 adapt 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 have to have 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 the 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.

 

Cons

• 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 also 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.

 

Conclusion

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.

 

Helpful Resource

The Complete Compost Gardening Guide
This book may convince you to give slower methods a try, as well as point out some of the many variations cold composting can take. Read our full review.

Most gardening books focus primarily (sometimes exclusively) on hot composting methods. They describe elaborate procedures for turning out the perfect batch of compost, including balancing nitrogen content and monitoring temperatures.

There is another way to compost—cold composting. The most obvious difference between the two methods is the temperature of the pile.

Each method has its advantages and disadvantages, making each one suitable for different circumstances. This week, we will examine the key features and pros and cons of hot composting, giving you an idea of the best applications for this technique. Next week, we will tackle cold composting.

Let’s get started!

 

Introduction to Hot Composting

Key to the process of hot composting is achieving the right balance of ingredients. Every hot compost pile needs some materials high in nitrogen (called “green materials”) and some materials high in carbon (called “brown materials”). The green materials feed the microbes that will do the work, thereby fueling the whole process. The brown materials add bulk and air flow, preventing anaerobic decay from taking over and creating a foul smell. Experts vary in their opinions of the proper balance between greens and browns, but a 1:1 or 1:2 ratio has consistently been proven effective for most home gardeners. For faster, hotter decomposition, all of the ingredients should be chopped small. Layering greens and browns is not essential.

Most gardeners also like to add an activator of some sort to the pile to ensure that the necessary organisms are present and ready for work. Many expensive preparations are available for purchase, but good-quality soil is quite sufficient for the purpose. Yarrow leaves are also beneficial, as they add minerals that can help the process go quickly and efficiently.

The compost pile should be a three-foot cube to allow the center to hold heat efficiently. A four-foot cube is even better, while a five-foot-cube is about the maximum size for effective composting.

Once the ingredients are properly balanced, special microorganisms take over the pile and begin the process of decay, emitting heat in the process. The heat builds up quickly in a well-made compost pile, ideally reaching temperatures between 120°F and 150°F.

From time to time, the microbes will use up all of the oxygen in the center of the pile, causing the temperature to drop. For this reason, the pile needs to be turned once a week or more, giving the tiny creatures access to fresh air and bringing organic matter from the outside of the pile into the center for processing.

At the same time, the moisture content of the pile should be considered. It should be moist, but not soggy. In dry weather, you will probably have to spray the pile down with a hose while turning it. In wet weather, you may want to place a tarp over the pile or make your compost in a fully contained bin to avoid drowning the microorganisms.

After about a month, the compost should look dark and crumbly (think chocolate cake crumbs), with no recognizable remnants of the former ingredients. At this point, the pile will no longer heat up when turned. The compost is technically finished, but it will benefit from one or two weeks of curing. This allows beneficial organisms a chance to repopulate the compost.

 

Pros

• Speed. Hot compost does its thing in short order, making the finished product available within three to four weeks.
• Reduced space needs. A hot compost pile can be built when you need it and removed in as little as a month. A cold compost pile can take up garden space for as long as a year, requiring a commitment in advance.
• Full control. Some gardeners like the amount of control hot composting gives them over the finished compost. They can easily adjust the temperature or decomposition speed by just turning the pile. To them, monitoring the pile is not a chore; it is an art.
• Sterilization. This is probably the #1 reason that gardeners choose hot composting methods. As the compost pile heats up, many pathogens and weed seeds get fried.
• Toxin degradation. Are you using ingredients that were not grown organically? Hot composting can break down and neutralize the pesticides present on that orange peel and the residue of any medications you might have administered to your horse that are now lurking in the stable bedding.
• No pests. Assuming the composting process is working correctly, that is. Most insects and rodents will leave a hot compost pile alone. A poorly made compost pile can still attract every type of pest from ants to raccoons.
• Helpful heat. The heat put out by a good compost pile can be put to work. One of the most common uses for this composting byproduct is heating a greenhouse.

 

Cons

• Difficulty. After unsuccessfully battling a compost pile that simply refuses to heat up or that smells and draws flies, many gardeners are tempted to give up on composting altogether. Hot composting is part art, part science. It takes practice. (Here’s a hint—make your compost in summer, when naturally hot temperatures will give you a head start.)
• Need for ample resources. A hot compost pile cannot be built in stages. You must have all of the necessary ingredients on hand and in the right balance from day one.
• Time and effort. A hot compost pile needs quite a bit of supervision. Besides weekly turning and watering, it will need to be monitored to ensure it is not too hot or too cold.
• Lack of natural equivalents. Most gardeners who use compost are already focused on growing healthy plants naturally. One question that recurs periodically is why hot composting is so widely advocated if there are no equivalents in nature. It appears that most of the composting done in the wild uses the cold method. While we do not know the answers for certain, it may be that there are benefits of cold composting that are lost in the process of hot composting.
• Microbe and worm death. Any small organisms that don’t like heat will die or escape the compost pile as it heats up, including worms, beneficial fungi, and some lower-temperature bacteria necessary to fight garden disease. Proper curing can remedy this, but it is important to recognize that hot compost still tends to be biased toward heat-friendly bacteria instead of the diverse, fungus-based biology commonly found in natural decomposition processes. Some composters feel that bacteria dominance makes the finished compost better suited to grassland plants than woodland plants. If the compost pile gets too hot (over 150°F) for more than a couple of hours, the problem is compounded significantly.
• Nutrient loss. Valuable nutrients are definitely lost if the compost pile overheats. If you smell a strong odor or see clouds of vapor rising from your pile, you can probably assume that most of the valuable nutrients are escaping into the atmosphere. Some gardeners feel that a certain degree of nutrient loss occurs in hot composting even if the temperatures stay below 150°F.
• Fire hazard. While not a common occurrence, spontaneous compost pile combustion can and does occasionally happen, for the same reason that wet hay bales sometimes burst into flames. Avoid this problem by monitoring the temperature and keeping it no higher than 150°F; making sure there are no pockets of dry material helps, as well. Also, if using wood ashes, make sure they are completely cool before adding them to the pile.

 

Conclusion

There are two main reasons that some gardeners prefer hot composting:

• To destroy weed seeds and pathogens.
• To have finished compost in a short amount of time.

In exchange for these two primary benefits, the gardener must devote considerable planning, attention, and effort to the project. For a very busy gardener, this is sufficient reason to turn to cold composting.

If, however, you have the time and resources to have a go at it, you may find hot composting to be rewarding and effective, especially for disposing of materials with potential chemical, disease, or weed seed residues. However, don’t let your pile get over 150°F, and allow it to cure for at least a week before using. This will help ensure that the finished compost retains as much of the nutrition and biological activity necessary for plant health as possible.

 

Helpful Resources

How to Build a Two-Bin Composter
Directions for building a compost bin that will make all that turning much easier.

The Christian Kids’ Gardening Guide
This fun book for children contains step-by-step instructions for making hot compost. Read our full review.