Garden Tips: Science behind how compost pile decomposes

To be a successful backyard composter, I think it is important to learn a little of the science behind composting, not just the basics of how to make a compost pile.

Decomposition is Mother Nature’s way of recycling. Without it, we would be buried in dead plant and animal matter. Technically, decomposition is the process by which organic materials, plant and animal, are broken into simpler compounds. A variety of decomposer organisms carry out the process by feeding on dead organic matter.

The most important primary decomposers are bacteria. They are the workhorses of a compost pile and predominate it early in the process. Their feeding helps break organic matter into compounds that other organisms can feed upon. As the bacteria feed and multiply, they use the carbon in the organic matter for creating new cells. With their feeding and multiplication, energy is released in the form of heat. This results in the compost pile heating up.

There are millions of bacteria in the world, so it is no surprise that there are different bacteria at work in a compost pile. The bacteria that get to work first are referred to as psychrophilic bacteria, working best at temperatures of 55 degrees. As these bacteria do their beginning work, the pile starts to heat up. When the temperature gets to about 70 degrees, mesophilic bacteria take over. The pile temperature continues to increase ,and thermophilic bacteria start to dominate once the pile temperature goes above 90 degrees. At temperatures above 160 degrees, all the bacteria start to die because it is too hot.

Other primary decomposers are invertebrate organisms, like millepedes, sow bugs and millepedes. They help speed the decay process by tearing the materials into smaller pieces with their feeding. This exposes more surfaces for the bacteria and other decay microorganisms, such as fungi and actinomycetes, to do work.

Primary decomposers are eaten by other organisms, such as springtails, mites and beetles. These secondary organisms are then eaten by a third level of larger consumers, including ground beetles, centipedes and ants.

When finished, a properly managed compost pile yields a dark, fairly stable mix of complex organic compounds. Quality compost is a dark, uniform crumbly material with no sticks, twigs or other distinguishable materials. When added to your garden soil, compost makes the soil more productive by improving soil structure, adding nutrients and increasing nutrient retention. Some refer to it as black gold because it is a valuable component of healthy soil.

The fall composting and waste reduction workshop will be from 9:30 a.m. to noon Oct. 31 in the conference room of the Mid-Columbia Library at 1620 S. Union Street in Kennewick. A discussion on recycling, burning laws, household hazardous waste disposal and litter laws will be followed with a program about composting yard and kitchen waste. Participants will receive a composting bin and softbound book. The program is free, but seats are limited. Preregister by calling 735-3551.

This story was originally published October 15, 2015 at 3:20 PM with the headline "Garden Tips: Science behind how compost pile decomposes."