WSU CAHNRS

Washington State University Extension

Garden Tips

DECOMPOSITION PART OF COMPOSTING PROCESS

GARDEN TIPS – written by Marianne C. Ophardt
WSU Extension Faculty
for the Tri-City Herald, Kennewick, WA Written October 18, 2015

I will be teaching a composting workshop at the end of this month. 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 decomposition we would all be buried in dead plant and animal matter. Technically, decomposition is the process by which organic materials, both plant and animal, are broken down into simpler compounds. A variety of “decomposer” organisms carry out the process by feeding on dead organic matter.

The most important primary decomposers of organic matter are bacteria. They are the “workhorses” of a compost pile. They predominate in the compost pile early in the process. Their feeding helps break organic matter down into compounds that other organisms can feed on. As the bacteria feed and multiply, they utilize 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 a variety of different bacteria at work in a compost pile. The bacteria that get to work first are referred to psychrophilic bacteria, working best at temperatures of approximately 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 off because it becomes too hot.
Other primary decomposers are invertebrate organisms, like millepedes, sow bugs, and millepedes. They help speed the decay process along by tearing the materials into smaller and smaller pieces with their feeding. This exposes more surface area for the bacteria and other decay microorganisms, such as fungi and actinomycetes, to do their work.

As part of the cycle of life that happens in a compost pile or naturally on a forest floor, the primary decomposers are eaten by other organisms, such as springtails, mites, and beetles. These secondary organisms are in turn 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 finished compost is a dark uniform crumbly material with no sticks, twigs, or other distinguishable materials. When added to your garden soil, quality 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.

Garden Tips, WSU Extension, Benton County, 5600-E West Canal Drive, Kennewick, WA 99336-1387, 509-735-3551, Contact Us

WSU Extension, Franklin County, 1016 North 4th Ave, Pasco, WA 99301-3706, 509-545-3511, Contact Us
© 2017 Washington State University | Accessibility | Policies | Copyright | Log in