The Community Inside the Compost Pile

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We have been learning to watch what a compost pile does before deciding what to change.

When a pile warms, settles, changes smell, loses recognizable material, or eventually cools, we are seeing the results of processes that are mostly hidden from us. So, who is doing the work?

It is tempting to think of the microorganisms in compost as one group of workers that moves into the pile and steadily breaks everything down although the actual process is much more dynamic.

A compost pile contains a community of decomposers, and that community changes as the pile changes.

At the beginning, fresh materials provide certain kinds of readily available food. Microorganisms suited to those materials and conditions begin using them changing the pile structure. Materials break down, heat may be produced, oxygen and moisture conditions can change, and some of the easier-to-use compounds become less available.

Those changes create different conditions for the organisms that come next. This means decomposition is not simply a matter of the same organisms doing the same work until the pile is finished. Different groups become more or less active as the available food and surrounding conditions change.

Bacteria and fungi are important primary decomposers, and other organisms participate as well. As decomposition progresses, the community can shift again. In an actively heating pile, organisms adapted to higher temperatures may become more prominent. As the pile cools and matures, organisms suited to cooler conditions return or become more active, and larger organisms may become increasingly noticeable.

When we manage moisture, air, materials, structure, and disturbance, we are not simply managing a pile of organic matter, we are changing the habitat in which the decomposer community works.

We do not need to memorize every organism to begin understanding this relationship.

For now, the important principle is that as the compost pile changes, the decomposer community changes with it.

The next time you look at a compost pile, consider what has changed since the materials were first combined. Are the original materials still easy to recognize? Has the pile warmed and cooled? Has its volume changed? Are fungi, insects, worms, or other organisms becoming easier to see?

Those observations are clues that decomposition is moving through time.

What change do you notice most clearly as one of your compost piles ages?

When you observe a compost pile over time, which change do you notice most easily?

The pile warms and later cools.

The materials become harder to recognize.

The pile loses volume.

Fungi or fungal growth becomes visible.

Worms, insects, or other organisms appear.

Smell and texture change.

I have not watched one pile closely enough yet.

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