Permaculture blog

Session 6: The art of composting

Published by Sam Page on 28 May 2012

The Permaculture group met on May 26th to discuss the vital questions of composting.  We looked at why we compost, from maintaining the health and organic content of our soil , to reducing land fill and its consequences, to having fun. 

We recognised that it a spontaneous process, and the composting organisms require four + equally important things to work effectively:

  • Carbon — for energy; the microbial oxidation of carbon produces the heat, if included at suggested levels.

    • High carbon materials tend to be brown and dry: straw, sawdust, leaves,
  • Nitrogen — to grow and reproduce more organisms to oxidize the carbon.

    • High nitrogen materials tend to be wet and green (or colourful, such as fruits and vegetables, grass cuttings, weeds).
  • Oxygen (i.e. air) — for oxidizing the carbon, the decomposition process.
  • Water — in the right amounts to maintain activity without causing anaerobic conditions.
  • Warmth - provide a 'duvet' in winter...


The right mix is needed for good hot composting, and the most efficient composting occurs with a carbon:nitrogen mix of about 30 to 1. Nearly all plant and animal materials have both carbon and nitrogen, but amounts vary widely, (dry/wet, brown/green).  Fresh grass clippings have an average ratio of about 15 to 1 and dry autumn leaves about 50 to 1 depending on species. Mixing equal parts by volume approximates the ideal C:N range. Composting for dummies gives some relative values. 


With the proper mixture of water, oxygen, carbon, and nitrogen, micro-organisms break down organic matter to produce compost.  The composting process is dependant on micro-organisms to break down organic matter into compost. There are many types of microorganisms found in active compost of which the most common are:-

  • Bacteria - The most numerous of all the bugs found in compost.
  • Actinomycetes (Actinobacteria) - Common in soil, fresh and sea water; necessary for breaking down cellulose/ chitin products such as newspaper, bark, etc. Mostly aerobic; few pathogens (mycobacteria of TB) and source of antibiotics.
  • Fungi, Molds and Yeasts - help break down materials that bacteria cannot, especially lignin in woody material.
  • Protozoa – microscopic,  motile organisms (amoeba, ciliates, flagellates; some serious pathogens); help consume bacteria, fungi and micro organic particulates.
  • Rotifers – near-microscopic ‘wheel animals’; help control populations of bacteria and small protozoans. Parthenogenic reproduction.

In addition, earthworms not only ingest partly composted material, but also continually re-create aeration and drainage tunnels as they move through the compost.

Also mites (related to spiders), millipedes, sow bugs (flat, fat, segmented, eat debris), springtails, beetles, ants, fly larvae, nematodes and flatworms.

There are two main composting methods:  Hot (thermophilic) and Cold

The Hot method is aerobic, needs turning or tumbling, needs enough volume to maintain heat (a cubic metre or well insulated), good proportions of green/brown, more work, quicker.

The Cold method tends to be anaerobic if not turned regularly; also known as ‘dump and run’, allows worm access, may take more than 6 months

We considered the special forms of composting, including Grub composting using the black soldier fly larvae, Bokashi composting and the use of ‘Effective Microbes’ (EM), Compost teas, Hugelkultur and ‘hotbeds’, Humanure and compost toilets, and wormeries.

Then we went and looked at practical garden methods, the common boxed-in heap, the ‘Dalek’ cone , the ‘Green Joanna’, Tumblers and Wormeries. Most of the enclosed methods will take food waste.

Since this session, I have been able to get three good 50 gallon drums suitable for making compost tumblers cheaply and relatively easily.  If anyone is inspired to help, please get in touch and come and have a look.

This post was written by Barney Rosedale