Building a Hot Compost Pile

A hot pile is the holy grail of home composting. By providing the proper conditions, microorganisms will continually build up heat as they break down organic matter in your compost pile. As the temperature increases, increasingly effective bacteria move in and break down tough organic matter at a much faster pace than larger decomposers like worms and beetles. With the proper conditions, a hot pile will break down into finished compost in as little as four to six weeks. Getting those conditions right can be challenging for even experienced composters, but a following a few guidelines will set you up for success.

Carbon to Nitrogen Ratio

The most important consideration for your compost pile is the ratio of carbon to nitrogen (abbreviated C:N) in the materials you use. Carbon-rich materials are commonly called “browns,” and include things like dry leaves and pine needles, wood chips, sawdust, and shredded paper. Nitrogen-rich materials, referred to as “greens,” include fruit and vegetable scraps, grass clippings, coffee grounds, and chicken manure. The ideal C:N ratio is 30:1, by weight, and you should balance your materials to achieve a ratio in the appropropriate range. Since each potential compost ingredient has its own C:N ratio, for ideal conditions you have to do some complicated math. If you have five pounds of fresh grass clippings (which has a C:N ratio of 20:1), you could balance it with only 0.16 pounds of sawdust (which has an extremely high C:N ratio of 500:1) or 1.125 pounds of dry leaves (with a C:N ratio of 60:1).

Grass clippings have a C:N ratio of about 20:1, putting them on the nitrogen-rich end of the spectrum.

While mathematically calculating by weight can be helpful, especially when dealing with materials with extremely high or low C:N ratios, there are alternate methods for those who aren’t worried about being exact. Most materials will be more easily measured by volume—a five-gallon bucket or a 32-gallon trash can—than by weight. Thus, an easy rule of thumb to achieve a C:N ratio near 30:1 is to use two parts browns (typically drier and lightweight) to one part greens (typically wetter and dense). While materials with extreme ratios, especially shredded paper, wood chips, and sawdust, can throw off the ratio, this simple, volumetric measurement will generally produce an acceptable ratio for hot composting.

If your ratio is off, you will know it very soon. Compost piles with too much nitrogen will go anaerobic, producing smelly ammonia compounds. Compost piles with too much carbon, however, will simply fail to heat up. The solution is as easy as adding more of the necessary material as you turn your pile, bringing the overall ratio closer to the ideal 30:1.

Size

Building your compost pile to an appropriate size is a crucial but often-overlooked step for hot composting. Heat is a byproduct of the decomposition process, but if a pile is smaller than 3’x3’x3’ (a cubic yard), it simply will not retain enough of that heat for the powerful decomposers to move in. Most commercially available compost bins and tumblers are too small to meet this threshold and won’t sustain hot compost. You can certainly produce compost from these smaller bins, but at a much slower rate than you would with a hot pile. You can certainly go larger than 3’x3’x3’, but any larger than 5’x5’x5’ usually becomes too unwieldy for the home composter.

Stockpiling fall leaves is an easy way to get a large volume of carbon-rich material.

Many home composters have trouble coming up with enough material for a hot pile all at once. Stockpiling resources is one way to go, perhaps saving fall leaves through the winter to mix with grass clippings in the spring. Also consider turning to your community for extra resources. Your neighbors are likely glad to part with their own yard waste, and you may be able to convince them to give you their food scraps, too. If you have friends with chickens or rabbits, see if you can have their manure or used bedding. Many coffee shops give away their used coffee grounds, and yard maintenance companies might be willing to save themselves a dump fee and drop off their debris at your house. Raid the office paper shredder, as long as there’s no plastic or wax coatings. And if all else fails, check online postings to see if people have free organic material they’re giving away.

Moisture

Water is another important part of the compost process, and it has to be at just the right levels for a compost pile to heat up. Keeping the moisture content between 40-60% is ideal. Your materials should feel like a wrung-out sponge—wet, but without dripping when you squeeze it. A dry compost pile is simply not a good habitat for most decomposers. Too much water, however, will keep the organisms in your pile from accessing oxygen, turning the compost process to the much smellier and slower anaerobic decomposition.

Oxygen

Oxygen is the final piece of the hot compost puzzle. Hot composting is an aerobic process, after all, and needs a constant supply of oxygen to keep working. Turning your pile weekly is the best way to keep your pile aerated and your decomposers respiring. The best way to turn compost is to physically move the whole pile from one spot to another, so keep that in mind when choosing the type of bin to use. With a three-bin system, for example, you simply move it from one compartment to the neighboring one, while a mesh cylinder can be unhooked and relocated adjacent to the existing pile, moving back and forth each week. Whatever your system, be sure to consider the space needed for the turning process when locating your compost pile.

While turning the pile, attempt to move material from the center of the pile to the outside and vice versa for even decomposition. Monitor your moisture levels, and add water every 6-8” as necessary to keep the water content between 40-60” throughout the pile. You can also take the opportunity to break up any clumped material and pockets of bad-smelling anaerobic decomposition.

Don’t Sweat It

Hot composting is the best way to have ready-to-use compost in a matter of weeks, but it certainly doesn’t work for everyone’s lifestyle. Fortunately, everything breaks down with enough time, and you can count on a variety of worms, beetles, fungi, bacteria, and other organisms to more slowly break down your pile at lower temperatures. Depending on contents and moisture level, a passive pile will produce compost in anywhere from six months to two years.

Top 5 Benefits of Compost

Compost is extremely beneficial to your soil, as most avid gardeners know. Whether worked into the earth or applied as a top dressing, compost can give your plants extra vigor as they grow. Even people who regularly use compost, however, are surprised at just how many ways it can improve their soil with its rich mix of organic matter and living organisms. Below are the top five benefits of compost.

1. Supplying Nutrients

To many people, compost is just another type of fertilizer. They use it simply for its supply of nitrogen, phosphorus, potassium, and other micronutrients. And while compost is a good source of a wide variety of those elements, it is not a concentrated source of specific nutrients as commercial fertilizers are. While that does mean that it’s difficult to use compost as a magic bullet to cure specific deficiencies in your plants, it comes with many upsides. Compost releases its nutrients slowly, over months or even years, whereas commercial fertilizers are typically quickly released and quickly depleted in the soil. Compost also generally features a wide variety of micronutrients, as its composition reflects that of its source materials. This can help prevent plants from developing deficiencies of minor elements like manganese or calcium, which are more likely to arise when relying on an NPK fertilizer.

2. Adding Organic Matter

Most home sites are not chosen for their fertile land, leaving homeowners to struggle with their native soils. While landscape plants can be selected to suit the existing conditions, it’s particularly hard to grow fruits and vegetables in mucky clay or quick-draining sand. Compost can come to the rescue, adding rich organic matter into troublesome soil to create a better growing medium. Not only does compost contain decomposed plants and food scraps, which nourish the soil, it is teeming with fungi, bacteria, and other organisms. These create a dynamic food web in your soil that has far-reaching effects for soil health. Compost is also rich in carbon, and adding it to the soil is a form of carbon sequestration that counters greenhouse gas emissions.

3. Building Soil Structure

Soil is not just one big block of dirt. It is a mix of sand, silt, clay, and organic matter in varying ratios. The spaces between the particles are known as pores, and it is through these pores that air, water, and plant roots move. It is easy to compact the soil, however, and collapse those pores. Compacted soil usually goes hand in hand with new construction, which has seen months of heavy foot and vehicle traffic around the site. Clearing a site of vegetation also usually leads to compaction, as the roots of growing plants are important for establishing and maintaining pore spaces. Not to mention, all the animals and microorganisms the vegetation supported are equally vital for healthy soil structure. Even areas that have been cultivated as lawns can be heavily compacted, the effect of years of foot and mower traffic and a root system that only reaches down a couple inches. Simply mulching with compost can help rebuild soil structure by introducing worms, beetles, fungi, and other organisms that work the soil and create new pores. Tilling the compost into compacted soil can also add diversity to the mix of soil particles, but it runs the risk of destroying any existing organisms in the soil.

4. Retaining Water

One major consequence of improving soil structure is also improving its capacity to receive and store water. When precipitation hits the ground, it can only sink into the soil if there is open pore space to absorb it. Otherwise, it runs off across the surface, eroding topsoil and picking up contaminants along the way. Soil amended with compost is able to capture more of that water and hold it right where plants need it—in the ground. And a nice thick layer of compost as a top-dressing is great for keeping the soil cooler and reduce moisture lost to evaporation.

5. Reducing Waste

In the United States, about 40% of the food that is grown is never eaten. There is more food in landfills than any other single material, where its anaerobic decomposition releases methane, one of the most potent greenhouse gases. That doesn’t even include other organic materials like yard waste, greasy pizza boxes, and shredded paper that are all excellent ingredients for composting. Composting these organic wastes reduces the amount of material send to landfills and sequesters carbon instead of releasing it into the atmosphere. Composting at home cuts out the impact of trucking your waste to a commercial facility, but those commercial facilities also have the ability to compost many materials that are difficult to deal with in a backyard system. Even if you don’t compost at home, participating in a green waste program is an important contribution to reducing waste in landfills.

Composting Methods 2: Outdoor

For those with outdoor space, there are many composting options available to suit every level of commitment. One of the first considerations for backyard composters is usually the issue of space. While a rural property might have plenty of room for a sprawling passive compost pile, it would likely be a nuisance on an urban lot. Pests are typically an equally important consideration—a yard plagued by raccoons might be unsuitable for any type of open piles or bins. And finally, the amount of work you are willing or able to put into your compost will dictate what methods are best. A compost system that doesn’t work for your lifestyle will be abandoned

Passive Composters

Passive composting is an easy and low-maintenance way to put your organic waste to good use, simply relying on natural decomposition processes to produce compost. It can be as low-tech as a heap in the back yard, a homemade bin system, or a durable plastic bins designed for this style of composting. Not only do most purpose-made passive composter contain odors, keep out pests, and have a smaller footprint than a sprawling compost pile, they simplify  the task of harvesting finished compost with a hatch at the bottom. While the effort needed for passive composting is very low, the time it takes to make compost is quite long, typically between 6 months to a year.

Compost tumblers will keep pests out, but have trouble letting decomposers in.

Compost Tumblers

Compost tumblers offer the benefits of an enclosed compost system, but they also have the ability to turn and aerate the contents for faster decomposition. There are many styles of compost tumblers on the market, but most can produce finished compost in a few months with the right mix of materials. There are a few downsides to tumblers, though. Because of their enclosed design, there is no connection to the native organisms in the soil. A compost pile or bin located on the ground has an easy path for earthworms, beetles, microbes, and other decomposers to move in and do their work, but a compost tumbler is closed off from many of these organisms. It also tends to dry out faster than other types of bins in warm weather, as all sides are exposed to the air and conduct heat to the compost inside. Most compost tumblers available are also too small to retain the heat generated naturally from decomposition which kills seeds, root fragments, and pathogens.

Three-Bin Systems

A three-bin system is great for those who are able to devote more time to managing their compost pile and also have room for a larger setup. It is one of the best setups for a hot compost pile, which is an extremely fast way to compost and also kills seeds, root fragments, and pathogens because of the high temperature it works at. The tradeoff is the necessity to frequently turn the compost—literally flipping the whole pile over weekly or more often. You add material to one bin until it is full and then move it into the adjacent bin to turn it, moving it back and forth every week. The third bin is used to once again collect material for the next pile.

This plastic mesh bin can be unclipped and repositioned to make it easy to turn the compost pile.

Portable Bin Systems

Another great option for building a hot compost pile is a removable bin. This can be a commercially available plastic product, a set of DIY hinged wood and wire panels, a simple cylinder of metal mesh, or many other creative designs. The key feature is that the bin can be unwrapped from the compost pile—which should hold itself up if all is well inside—and repositioned next to the existing pile. Then, like with the three-bin system, the compost is turned into the new location. Portable bins can be very cost-effective and can be great for those who don’t have space for a three-bin system, or who want a less permanent option.

Worm Bins

Finally, worm bins are another option outdoors! Areas with mild winters can take advantage of worm bins year round, but in northern climates like in Spokane and Coeur D’Alene, worms must retreat below the frost line to survive. That means that it is important to give your worms an escape route, whether by using a bin that gives your worms contact with the soil or by repatriating your colony every fall. Outdoor worm bins can do double duty as furniture or be attractive landscape features in their own right. They can also be integrated into existing garden areas, maximizing the impact of the worm castings and minimizing your own effort.

Composting Methods 1: Indoor

For people who decide to start composting their organic waste, the choice of what method to use can be overwhelming. A successful composting journey, however, starts by picking a method that will work for your lifestyle and composting goals. To keep yourself from becoming frustrated, it’s important to first evaluate how much time and space you have to devote to composting. Also consider what materials you produce, whether you have pests like raccoons you need to guard against, and whether you want to compost through the winter. Weighing your needs against the features of each composting method will help you decide which to choose. 

Indoor composters are primarily designed to deal with kitchen scraps and other food waste. They can be used year-round and are great for apartments, offices, and other locations that lack outdoor space. They are also often used in conjunction with outdoor systems to take advantage of the benefits of each. While you can simply take a container and construct an indoor compost pile in the same way you would an outdoor pile, it’s very difficult to achieve the right balance of materials, moisture, and oxygen. An unbalanced pile tends to produce foul-smelling methane and attract pests, which are side effects which are generally not welcome indoors. Specialized indoor composting techniques bypass those complications, however, allowing you to peacefully coexist with your decomposing food.

Worm castings are dark, crumbly, and full of nutrients.

Worm Bins

Worm bins are by far the most popular method of indoor composting. As the name suggests, worm bins are typically a container or series of containers housing a colony of worms. While they use carbon rich materials like shredded paper as their bedding (as well as an occasional snack), the worms are primarily a way to turn your nitrogen-heavy food scraps into rich worm castings. If you’re feeding your worms right, the process is odor free and suitable for small apartments and enclosed spaces. There are a few foods that shouldn’t be fed to the worms, though. Meat, dairy, and fats can go rancid before the worms get to them and also tend to attract pests. Alliums, like onions and garlic, and brassicas, like cabbage and broccoli, are naturally strong-smelling and create even more odor when decomposing. Spicy food and citrus can also be harmful. These limitations can be the main reason not to use a worm bin—if you can’t produce enough worm-friendly food scraps, the worms will starve!

Electric Composters

There are several models of electric composters available; these grind up food waste and heat it up to speed decomposition, resulting in finished compost in just a couple weeks. Unlike the majority of compost methods, you can include meat, bones, dairy, and oils, as long as the quantities aren’t too great. While these appliances are fast and odorless, they do tend to be noisy as they grind and turn the food scraps.They also use energy, which can be a downside for those trying to lower their carbon footprint. And on top of paying for the electricity to run the composter, the units themselves are quite expensive, starting around $300.

Bokashi

Bokashi is a relatively new home-composting technique. It uses an airtight bucket and a blend of microbes to ferment food scraps. Food waste is added to the bucket and sprinkled with a dry material, commonly referred to as bran after the most popular choice of substrate, that has been inoculated with microbes. The bran is added every time scraps are until the bucket is full, at which point the sealed bucket is put aside for two weeks to ensure that all the material is fully fermented. Waste liquid, which can be diluted and used as fertilizer, should be regularly drained off while the bucket is being filled and during the final two-week curing process. The finished product with bokashi is often referred to as “pre-compost” as it has not broken down into crumbly, dark brown material. The nutrient- and microbe-rich material can be incorporated into an existing outdoor compost pile or buried in fallow ground, where it will rapidly decompose into finished compost in just a couple weeks.

While bokashi fermentation is an anaerobic process, it is different from the methane-producing anaerobic decomposition that occurs in landfills and soggy compost piles. Bokashi instead has a slightly acrid pickled odor, like sauerkraut or kimchi. The airtight bucket contains these odors, however, except when the lid is opened to add material. Because of the nature of the fermentation process, it is safe to compost dairy, fats, and even small amounts of meat and bones. Unlike worm bins, you can feed your bokashi bin as little or as much as you produce, simply adding bokashi bran as necessary. The necessity of burying the bokashi can be challenging for those with no outdoor space, but the compost can be finished in a soil-filled bin or even gifted to a fellow composter or community garden.

Introduction to Compost

If you are interested in becoming more self-sufficient, growing your own food, producing less waste, and lowering your carbon footprint, composting at home can help with all of those objectives. Compost is not a new idea. Beyond the fact that human cultures have been producing and using compost for centuries (if not millennia), Mother Nature has been composting for as long as organic matter has existed.

What is compost? It’s simply decomposed organic matter. All organic matter decomposes eventually, but composting generally involves techniques that harness natural processes to speed up decomposition. The final product is dark, crumbly, earthy-smelling, and full of nutrients and microorganisms that are beneficial to plants.

Finished compost is dark and crumbly.

When many people think of compost, they think of worms. And while worms are certainly one decomposer—in fact, one method of composting relies exclusively on worms—they are a relatively minor part of the decomposition process. Worms and other creatures like snails, millipedes, sow bugs, and some types of nematodes, and fly larvae are all visible organisms that work on decomposing the organic material in your compost pile, but the powerhouses are all much smaller. Microorganisms such as fungi, bacteria, and actinomycetes (an unusual bacteria that forms colonies like a fungus) exist in such huge quantities that they are able to break down organic matter at a much faster rate than their larger counterparts, often without you ever seeing them.

Also surprising to most people are the extreme temperatures at which decomposers work. A class of bacteria known as psychrophiles are active at temperatures all the way down to 0°F, although they’re most effective around 55°F. As they oxidize organic material, they produce heat. If your compost pile is large enough to retain this heat, it becomes habitable by the mesophiles. These are your everyday bacteria that survive temperatures from about 40°F to 110°F, with the active range between 70°F to 90°F. Mesophiles are much more effective composters than psychrophiles, and they further warm up the pile to introduce yet another class of bacteria: the thermophiles.

Thermophilic bacteria are rapid decomposers that operate from 100°F up to as much as 200°F, though most home compost piles peak between 160°F and 180°F. These high temperatures will kill weed seeds and pathogens in the compost, which is especially important in commercial composting facilities. Temperatures will naturally drop again after 3-5 days as the bacteria use up their resources, but the process can be restarted by turning the compost pile to aerate and add necessary moisture. It takes a delicate balance of ingredients to reach the thermophilic stage, but mesophilic composting is still quite effective and much easier to accomplish.

Your finished compost will support a complex food web including many of the same macro and microorganisms that aided in the decomposition process. It will also be pH neutral, as the decomposition process buffers acidic or alkaline material. No matter what the original material, the compost will be dark and crumbly and smell like earth. There are often some materials, such as larger chunks of wood or fruit rinds, that don’t completely compost by the time the rest of the pile is finished; these can be screened out and added to the next compost pile. The finished compost can then be applied to your landscape plants and produce, adding vital nutrients to help you grow your next round of compost ingredients.