Compost is made through the process of decomposing. That much should be fairly obvious. But what actually happens during decomposition that changes your grass, leaves, stems and other organic matter from what it was into the beautiful, fluffy black stuff that is compost? As it turns out, decomposition is essentially the process of eating and pooping, to put it crudely.
Plant material is made up of all the nutrients that are needed for growth. However, they are in a raw form that is inaccessible to plants. Along come various micro- and macroorganisms, which consume, digest and excrete those substances, thus breaking them down into elemental forms that plants can then absorb back into their structures to form new stems and flower and leaves, etc. Just as, when you eat meats and vegetables, your body digests the foods and breaks them down into useable nutrients and unusable wastes, so these organisms, through eating and digesting break down the raw substances into usable forms.
The Microogranisms of Compost
The microorganisms involved in decomposition are made up of three groups of bacteria and various fungi and actinomycetes. Without getting too technical here (oops, too late!), the bacteria come in three basic flavors, categorized by what temperatures at which they work. When you first create a compost pile the materials are at roughly local, or cool temperatures. Psychrophiles are the first grouping of bacteria that begin to operate on the compost right away. These bacteria consume the raw materials and release amino acids and heat. The heat is not what breaks down the compost pile, contrary to popular belief. Rather, heat is the byproduct of the bacterial metabolism that takes place in the compost pile.
As the temperatures climb, other forms of bacteria take over. First, mesophiles (meso=middle) begin the attack, and later thermophiles (thermo=heat) take their turn. Most of the work in the compost pile is done by the mesophiles, but once they raise the temperature up to around 100 degrees they work themselves
out of a hospitable environment. Then the thermophiles take over and they can raise the temperature to as high as 160 degrees F. The compost pile will usually stay at this temperature for only a few days while the thermophiles do their work, after which the pile will cool down to below 100 and the mesophiles take over again. All the while these bacteria are doing their work, fungi and actniomycetes are working alongside them, all playing their parts in break down the tough raw materials and turning them into compost.
These microorganisms form the foundation of decomposition. Indeed, without them there would be no decomposition. Never the less, they are not the only organisms at work in the compost pile.
The Macroorganisms of Compost
There are also important macroorganisms at work throughout the decomposition process, and by far the most important of these is the earthworm, though other creatures such as mites, grubs, insects and nematodes participate as well. These larger creatures break down larger materials into smaller bits that are more readily accessible to the microorganisms, thus speeding up the process dramatically. The earthworm eats organic matter and leaves behind “castings”. These castings are rich in plant nutrients, and that is why some garden centers sell worm castings as a form of compost. An earthworm can produce its weight in castings each day. Within a few days of creating a compost pile you should be able to find scores or hundreds of earthworms in your pile, if you dig through and look for them.