Composting 101

Steps to Make Compost

Composting doesn’t have to be difficult, nor does it require a strong back, large acreage, livestock waste or expensive bins. Even apartment-dwellers or those with physical limitations can put their kitchen waste to work. The following are composting techniques from the simplest to the most strenuous.

The easiest method of using kitchen waste and thin paper goods is to bury them. Each day gather your kitchen waste and choose a spot near a plant, dig a small hole with a trowel, plop in the food waste and cover it up. You’ve just fed your microbes, which will feed your plants, and it took maybe five minutes if you didn’t have to look for the trowel. You may also acquire some surprise volunteer vegetables the next season. If you have difficulties with animals digging up compost, then sprinkle cayenne pepper over the dirt, or cover the area for a few days.

If digging is out of the question, use your blender. Remove bones, large pits and tough plant stalks at which your blender might balk. Place peels, plate scrapings, tissues, paper towels, leftover beverages, etc., add water to fill the container, and blend away. A watery consistency is best. Pour this wonderful soil food around your plants; even your potted plants will love it. A dose of blended compost will last potted plants for months, so don’t overdo it; your soil microbes can only eat so much. If pouring it in the garden, you can be more generous. If your batch is thick enough to leave a bit on the soil surface and you’re afraid of attracting flies, then kick some dirt over the top. Simple.

The next step up is cold composting, which is throwing your biodegradable waste into a stationary, closed compost bin. Without being turned this compost won’t heat up much, and if you don’t layer the fresh stuff such as kitchen waste (nitrogen source) with dirt, dry leaves or dry grass (carbon source), then it will probably smell and attract flies and rodents. It will, however, gradually turn into decent compost, which is usually raked out the bottom.

If your compost bin is a tumbler, meaning that the barrel that holds the compost can be externally turned, then you should have hot compost. Done correctly, tumblers produce good compost in a short period of time. If too wet the tumbler becomes a hard-to-turn smelly, drippy nightmare. Loading the debris and unloading the compost can be challenging for the back, and since you can’t add to the load while it is composting you may have a back-up of compostables waiting for their turn in the hopper.

The next, more difficult type of composting requires a shovel. Find some poor soil, dig a hole of a size that can accommodate several day’s to a week’s worth of green waste, and then layer your green waste as it becomes available with dirt until the hole is filled. This method is particularly good for creating future no-dig vegetable beds in-situ; vegetables and other herbaceous plants love a more bacterially active soil than woody plants, which do like their fungal webs. You may plant in these beds in a month or two, depending on your weather and what you buried. Burying organic material sequesters carbon and gasses such as methane in the soil. Did you realize that you can bury clothing, too? Natural fabric clothes, bedding, towels, untreated wood products such as cardboard and old lumber, and even old rusty hardware, nails and wire can all be layered, watered in and buried.

Then there is the three-bin composting technique, which requires regular turning. Bins can be made of old wooden pallets wired together, or can be lovely permanent structures. Each bin should hold a minimum of three cubic meters of compost or else the pile won’t heat up. Everything except woody cuttings are layered into the first bin until it is full. Usually a 3:1 carbon: nitrogen balance works well. Carbon-based matter is the stuff that is pretty dead already such as dry leaves, brown grass clippings, cardboard, etc. Nitrogen-based ‘hot’ stuff includes green grass and weeds, fresh manure, kitchen scraps, and other things that still have some life left in them. Keep the compost materials only wet enough so that when wrung just a little drips out. You may have to cover your heap to keep it dry, or water it depending on your weather. The heap should heat up within days or else the recipe isn’t quite right. To heat up a stubborn pile add comfrey leaves, stinging nettle, or compost tea. After a couple of weeks, pitchfork the entire thing into the next bin, making sure to tuck what had been on the outside towards the middle. It will heat up again and in a couple of weeks you should be ready to give it the final turn into the last bin. Meanwhile you will have had the chance to start two new batches of compost.

Besides being a little taxing on the back, this method of composting, or any open-air method, releases methane into the atmosphere which contributes to global warming. The compost also reduces in size so you end up with a fraction of the bulk you started with.

Geoff Lawton of the Permaculture Research Institute recommends an enthusiastic 18-day compost method, which he demonstrates in his Permaculture youtube videos. He mounds a wonderful array of manures and dry materials in a three cubic meter pile, waters and covers it, turns it the fourth day and then every other day until the 18 days are up. The beauty of this quick-cooking compost is that the resulting pile of compost remains the same bulk as the original, and being covered releases little gas. The minus side is that it requires a lot of materials that those without access to farm animals and lots of dried matter will find difficult to collect. It also requires heavy exercise every couple of days.

No matter what your physical condition or living circumstances you can use permaculture techniques to feed your soil by using your own green waste. Find what works for you, and it’s guaranteed you will be as happy as your plants to be lessening your footprint in such a simple way.

Regular composting, also known as cold composting, involves placing a variety of organic materials in a compost bin, enclosure, or even just in a large heap, and leaving it there until it breaks down several months later. It’s a very slow process and typically takes 6 to 12 months. It can be sped up by turning the compost, that is, moving around the material at the bottom of the heap to the top and vice versa to mix it up and get more oxygen in there, but it’s still a long wait. But there’s a better way to do composting…

The Difference Between Hot and Cold Composting

The other approach to composting is hot composting, which produces compost in a much shorter time. It will effectively destroy disease pathogens (such as powdery mildew on pumpkin leaves), weed seeds, weed roots (such as couch and kikuyu) and weeds which reproduce through root bulbs (such as oxalis). This process breaks down the material much better to produce a very fine compost.

By comparison, the slower cold composting methods will NOT kill disease pathogens or weed seeds and roots, so if this compost is put into the garden it may spread weeds and plant diseases, hence the common advice not to (cold) compost diseased plants.

The other issue with cold composting is that it produces a coarser compost, with lots of large pieces of the original materials left over in the compost when the process is completed, whereas hot compost looks like fine black humus (soil), and none of the original materials are distinguishable.

Hot composting is a fast aerobic process (uses oxygen), so given volume of compost materials produce almost the same volume of finished compost. In contrast, cold composting is slow anaerobic process (without oxygen), it’s a different chemical process, and as a result, nitrogen and carbon are lost to the atmosphere, which causes a reduction in the volume of compost to 20% of the original volume.

Compost Microbiology

In the process of composting, microorganisms break down organic matter and produce carbon dioxide, water, heat, and humus, the relatively stable organic end product. Under optimal conditions, composting proceeds through three phases: the mesophilic, or moderate-temperature phase, which lasts for a couple of days, the thermophilic, or high-temperature phase, which can last from a few days to several months, and finally, a several-month cooling and maturation phase.

Different communities of microorganisms predominate during the various composting phases. Initial decomposition is carried out by mesophilic microorganisms, which rapidly break down the soluble, readily degradable compounds. The heat they produce causes the compost temperature to rapidly rise.

As the temperature rises above about 40°C, the mesophilic microorganisms become less competitive and are replaced by others that are thermophilic, or heat-loving. At temperatures of 55°C and above, many microorganisms that are human or plant pathogens are destroyed. Because temperatures over about 65°C kill many forms of microbes and limit the rate of decomposition, compost managers use aeration and mixing to keep the temperature below this point.

During the thermophilic phase, high temperatures accelerate the breakdown of proteins, fats, and complex carboydrates like cellulose and hemicellulose, the major structural molecules in plants. As the supply of these high-energy compounds becomes exhausted, the compost temperature gradually decreases and mesophilic microorganisms once again take over for the final phase of "curing" or maturation of the remaining organic matter.

Bacteria

Bacteria are the smallest living organisms and the most numerous in compost; they make up 80 to 90% of the billions of microorganisms typically found in a gram of compost. Bacteria are responsible for most of the decomposition and heat generation in compost. They are the most nutritionally diverse group of compost organisms, using a broad range of enzymes to chemically break down a variety of organic materials.

Bacteria are single-celled and structured as either rod-shaped bacilli, sphere-shaped cocci or spiral-shaped spirilla. Many are motile, meaning that they have the ability to move under their own power. At the beginning of the composting process (0-40°C), mesophilic bacteria predominate. Most of these are forms that can also be found in topsoil.

As the compost heats up above 40°C, thermophilic bacteria take over. The microbial populations during this phase are dominated by members of the genus Bacillus. The diversity of bacilli species is fairly high at temperatures from 50-55°C but decreases dramatically at 60°C or above. When conditions become unfavorable, bacilli survive by forming endospores, thick-walled spores that are highly resistant to heat, cold, dryness, or lack of food. They are ubiquitous in nature and become active whenever environmental conditions are favorable.

At the highest compost temperatures, bacteria of the genus Thermus have been isolated. Composters sometimes wonder how microorganisms evolved in nature that can withstand the high temperatures found in active compost. Thermus bacteria were first found in hot springs in Yellowstone National Park and may have evolved there. Other places where thermophilic conditions exist in nature include deep sea thermal vents, manure droppings, and accumulations of decomposing vegetation that have the right conditions to heat up just as they would in a compost pile.

Once the compost cools down, mesophilic bacteria again predominate. The numbers and types of mesophilic microbes that recolonize compost as it matures depend on what spores and organisms are present in the compost as well as in the immediate environment. In general, the longer the curing or maturation phase, the more diverse the microbial community it supports.

Actinomycetes

The characteristic earthy smell of soil is caused by actinomycetes, organisms that resemble fungi but actually are filamentous bacteria. Like other bacteria, they lack nuclei, but they grow multicellular filaments like fungi. In composting they play an important role in degrading complex organics such as cellulose, lignin, chitin, and proteins. Their enzymes enable them to chemically break down tough debris such as woody stems, bark, or newspaper. Some species appear during the thermophilic phase, and others become important during the cooler curing phase, when only the most resistant compounds remain in the last stages of the formation of humus.

Actinomycetes form long, thread-like branched filaments that look like gray spider webs stretching through compost. These filaments are most commonly seen toward the end of the composting process, in the outer 10 to 15 centimeters of the pile. Sometimes they appear as circular colonies that gradually expand in diameter.

Fungi

Fungi include molds and yeasts, and collectively they are responsible for the decomposition of many complex plant polymers in soil and compost. In compost, fungi are important because they break down tough debris, enabling bacteria to continue the decomposition process once most of the cellulose has been exhausted. They spread and grow vigorously by producing many cells and filaments, and they can attack organic residues that are too dry, acidic, or low in nitrogen for bacterial decomposition.

Most fungi are classified as saprophytes because they live on dead or dying material and obtain energy by breaking down organic matter in dead plants and animals. Fungal species are numerous during both mesophilic and thermophilic phases of composting. Most fungi live in the outer layer of compost when temperatures are high. Compost molds are strict aerobes that grow both as unseen filaments and as gray or white fuzzy colonies on the compost surface.

Protozoa

Protozoa are one-celled microscopic animals. They are found in water droplets in compost but play a relatively minor role in decomposition. Protozoa obtain their food from organic matter in the same way as bacteria do but also act as secondary consumers ingesting bacteria and fungi.

Rotifers

Rotifers are microscopic multicellular organisms also found in films of water in the compost. They feed on organic matter and also ingest bacteria and fungi.