In the pathway: Water and living soil, Urban permaculture
Advanced composting
Choosing the right composting method for your needs and resources.
Introduction
Composting is the art of turning a waste into a resource. Depending on the space, the climate and the available materials, several methods coexist: surface compost, windrow, vermicompost, Bokashi, woodland compost. Choosing well means composting effortlessly and obtaining a rich, living humus.
Background
Composting is a central act for maintaining soil organic matter, at every scale.
Who this guide is for
Everyone, from the flat to the large plot: each space has its method.
Why it matters
Clearly reduces the weight of the bins. Provides a free amendment. Feeds the soil with micro-organisms. Closes a fertility loop.
What to understand before starting
- Space suited to the chosen method (from 30 cm² vermicompost to 4 m² windrow).
- A balanced C/N mix: 2/3 brown (carbon: leaves, straw, brown cardboard) to 1/3 green (nitrogen: peelings, clippings).
- Aeration possible (except Bokashi, which is anaerobic).
Detailed steps
- Step 1
Surface compost
Spread the materials directly at the foot of the plants or on fallow beds. Cover with a little straw. Ideal for continuous upkeep with no chore. Medium speed.
- Step 2
Windrow compost (classic pile)
A pile of at least 1 m³. Alternating brown/green layers. Turn once at 6 weeks, then once at 3 months. Matures in 6 to 9 months. The go-to method for a large garden.
- Step 3
Vermicomposting
A stacked bin with Eisenia worms. No meat, garlic, onion or excess citrus. The worm 'tea' (leachate) is very rich in trace elements. Indoors or outdoors in shade.
- Step 4
Bokashi
An airtight bucket with an inoculant (EM-fermented bran). Anaerobic fermentation in 2-3 weeks. Accepts meat, fish, cooked food, citrus. The result is not compost but a pre-compost to bury 2 weeks before growing.
- Step 5
Woodland compost
Under trees and shrubs: a thick layer (15-20 cm) of dead leaves, RCW, chipped branches. No turning. Slow decomposition (12-18 months), very high quality.
- Step 6
Balance the C/N
Always about 2/3 brown (carbon) to 1/3 green (nitrogen). Too much green = bad smells. Too much brown = slow decomposition.
- Step 7
Aerated compost tea
1 kg of mature compost in 10 L of rainwater, aerated with an aquarium pump for 24 to 36 h. Its value against diseases remains uneven and debated (Scheuerell & Mahaffee, 2002).
Concrete examples
Common mistakes to avoid
- A pile too small (< 0.5 m³): it doesn't heat up, decomposition is very slow.
- Adding only clippings: compaction, fermentation, smells.
- Vermicompost in full sun: cooked worms.
- Bokashi with a non-airtight lid: putrefaction instead of fermentation.
- Composting diseased plants (blight, clubroot): you spread the pathogens again.
Tips & best practices
- Always keep a bag of dead leaves or shredded cardboard next to the composter: balance each green addition.
- Roughly shred before adding: decomposition twice as fast.
- Collect the worm leachate every week: use immediately, diluted 1/10.
Frequently asked questions
- My compost smells bad?
- Too much nitrogen / too wet / not aerated enough. Add brown (cardboard, straw), turn.
- How long for mature compost?
- 6 to 12 months in a maintained windrow. 3 to 6 months in well-managed hot compost. 18 months in cold compost.
- Compost and eggshells?
- Yes, finely crushed. A source of calcium, but very slow to decompose whole.
Sources
- RHS (Royal Horticultural Society) : Composting (rhs.org.uk/soil-composts-mulches/composting)
- Quiroz, M. & Céspedes, C. (2019). Bokashi as an amendment and source of nitrogen in sustainable agricultural systems: a review. Journal of Soil Science and Plant Nutrition, 19(1), 237-248.
- Scheuerell, S. & Mahaffee, W. (2002). Compost tea: principles and prospects for plant disease control. Compost Science & Utilization, 10(4), 313-338.