Composting: need-to-know.


Compost is organic matter that has been decomposed into humus after a period of time with the help of microorganisms. It’s an absorbent dark-brown material that preserves water, minerals and nutrients.

There are 2 types of composting: aerobic (with oxygen) and anaerobic (without oxygen). Aerobic composting reaches high temperatures and is a rapid, odourless process. Anaerobic fermentation gives lower temperatures, takes more time and contains odours.

I’ll only be explaining the aerobic methods of composting.

The benefits of compost.

Compost can be used as a fertilizer and overall soil improver (humus, nutrition, organisms, structure …). Its porous nature prevents erosion by soaking up water like a spunge. It also works as a natural pesticide. The diversity of organisms (especially inside mature compost) suppress a variety of diseases, infections and pests. And don’t forget it’s a win-win: free garbage disposal and free compost!

Kitchen scraps

Where to start?

Make a heap in a shadowy, windless spot that benefits just a few hours of sun. The pile should be at least 1 m² (10 ft²) to reach a beneficial temperature. It should be a well-balanced mix of green (high in nitrogen) and brown (high in carbon) organic matter on top of bare ground. Gently moisten the heap. All the seperate ingredients should be made as small as possible. Shred it, cut it and mash it to small pieces to get the best results!

As you can see in the picture below, I used pallets to seclude the organic matter.

Compost heap

Don’t forget to regularly turn the pile with a pitchfork to replenish the oxygen levels between the organic matter. Aerobic bacteria need oxygen to survive, whereas anaerobic bacteria, working at slower rates, don’t.

When you search the web, you’ll find a lot of different methods worth exploring on composting with various results (Berkeley method, Jean Pain method, Vermicomposting, Leaf compost …).

When to start?

You can actually start composting any time of the year, but cold weather will just prolong the process. The best time to start a heap is in summertime, when temperatures outside are warm as this benefits the decomposing of the materials. However, if you don’t have enough organic matter it’s better to wait and collect it on “waiting piles”.

What to add?

50% Brown (high in carbon):

  • Sawdust
  • Inkless cardboard and paper (egg carton, toilet roles …)
  • Dried leaves
  • Straw
  • Wood chips (branches …)
  • Wood ash (not too much)

Compost heap

50% Green (high in nitrogen):

  • Grass clippings (mix it well with other materials to avoid rot)
  • Fruit and vegetable scraps
  • Animal manure (horse, cow, chicken …)
  • Hay
  • Green leaves
  • Weeds (preferably seedless)
  • Coffee grounds
  • Urine
  • Seaweed

How does it work?

  1. Decomposition by mesophilic microorganisms (bacteria, funghi and archaea) intitiates at temperatures between 10°C and 40°C (50°F and 104°F). Acidity levels decrease and a lot of CO2 is released.
  2. Thermophilic microorganisms continue the decomposition, as temperatures rise between 41°C and 70°C (106°F and 158°F). Nitrogen is released as NH3. Most diseases, insect eggs, larvae and seeds die because of the high temperatures.
  3. When the temperature finally drops below 40°C again, mesophiles take over once more.
  4. After reaching environment temperatures, the compost will start the curing process. This is also the time when earthworms and other insects take on a part of the job. During this phase, the acidity (PH) stabilises.

Compost temperatures

The first 3 phases of the composting process take several weeks. The 4th phase (curing) can take up to several months.

When is it ready to use?

It’s better to use mature compost to prevent acids and pathogens damaging your plants. As it isn’t mature yet, it will also consume both nitrogen and oxigen already present in the soil to continue the decomposting process.

Earthworm in Compost

So when is it ready? Compost is ready to use when it looks, smells and feels like dark-brown earth. This can take up to several months depending on:

  • moist
  • mix of green and brown material
  • air
  • regularity of turns

There are several ways to speed up the process:

  • Turn the pile regularly.
  • Add chicken manure, seaweed and lots of nettles.
  • Add leftovers of former compost.

To speed up the process significantly, consider the Berkeley method (hot composting).


  1. Too dry?!
    – The organic matter looks dusty and dry, sometimes with a white layer on it.
    – The decomposition seems to have slowed down drastically.
    – Ants in your heap.Turn the pile and add water and green, nitrogen-rich materials.
  2. Too wet?!
    – Smell of rot or ammonia.
    – Water seeping out at bottom.
    – Top layers are clumped together.Turn the pile and add brown, carbon-holding materials.

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