Commercial compost tends to lack microbial life. Learn to make it correctly.

Updated: Dec 9, 2019

What exactly is compost?

This question – framed against dead soils, wacked-out weather and declining farm profits – carries huge relevance to our times.

With a growing focus on soil biology, some university researchers these days are including compost in agriculture field studies. Results tend to be mixed, and that’s not terribly surprising. Because by and large, little attention is paid to what exactly compost should be.

It’s common to find the stuff treated in published research as a generic source of organic matter, often produced from a small number of ingredients – say, green waste and animal manure. Such a recipe raises concerns. While it’s always unclear what may comprise “green waste,” it’s likely a collection of material pruned from live plants; add that to manure, and you’ll get runaway bacterial growth from the dense supply of nitrogen in those materials.

The resulting product may perform well as a fertilizer, and still delivers plenty of organic matter (that being the stated reason for including compost in most studies). But while a mass of bacteria is not necessarily bad, it is certainly imbalanced. What about fungus, nature’s other decomposer, so important to the mid- to upper-successional plants that we cultivate commercially?

And beyond that, protozoa, nematodes and microarthropods? It’s this diverse collection of life forms – what we call the Soil Foodweb – that creates rich nutrient cycling: one organism consumes another and secretes waste, contributing to a vast array of metabolic and chemical processes that make nutrients available to our plants as well as other microbes.

Farmers generally expect that, because they applied organic matter, microbes will begin growing. Technically, this is true: with the right techniques, microbes will, after several years, find their way back to a previously ill-treated farm field. But if the farmer also applies compost containing the needed soil organisms, the process of converting to regenerative agriculture takes a small fraction of the time, and just as promptly leads to greater farm profits.

If you're lucky enough to be situated near a producer of high-quality compost (like this one here in Northern California), your task of sourcing diverse microbes may be simplified. But most farmers don't have that luxury, which means it could pay huge dividends to learn composting skills. It's often a feasible and effective solution to produce material at small scale, by hand, one yard at a time; the microbe populations developed in this material can be further multiplied and, using other techniques, applied to large acreages.

Start with a recipe containing less green, nitrogen-rich things, and more brown, carbon-rich materials – anything that is woody, or was harvested as dead material. Put simply, carbon-rich substances feed fungi more than they do bacteria.

We also need diversity of microbial food materials, which means at least a half-dozen items – brown things like fallen tree leaves, wood chips and weeds trimmed brown; green things like plant prunings, mowed grasses and green weeds; and very-high-nitrogen items, like alfalfa, clover and manures.