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In the pathway: Getting started in permaculture

Mulch

A layer of material laid over the soil to keep it permanently covered, instead of leaving the earth bare.

Strawberry plants surrounded by a straw mulch that covers the soil.

Mulch: a layer of material, here straw around strawberry plants, that covers the soil, keeps in moisture, holds back weeds and feeds soil life as it breaks down.

Photo: Anja Meert · CC BY-SA 4.0 · source

Watch the videoLe mulch en permaculturePermaculture Design

Explanation

Mulch limits evaporation, smothers weeds, feeds micro-organisms as it decomposes, and keeps the temperature stable.

Refined definition

Mulch is a soil cover made of organic materials (straw, hay, dead leaves, RCW, coarse compost, dried grass clippings…) or mineral materials (gravel, stones, crushed tiles in dry contexts), applied in a more or less thick layer to protect the soil, limit evaporation, reduce weeds, feed soil life and stabilise the temperature.

Key points

  • Thickness and material

    Light materials (leaves, clippings) decompose quickly: they feed the soil well but must be renewed often. Structured materials (straw, RCW, wood chips) last the whole season and provide more protection.

  • Effect on soil structure

    As it decomposes, mulch increases organic matter and improves structure (aggregates, porosity), which favours water infiltration and rooting.

  • Soil life

    It creates a moist, dark microclimate ideal for earthworms, springtails and mycelium, which turn the mulch into humus and available nutrients.

  • Weeds

    It does not suppress all germination, but sharply reduces light at soil level: emergence is slowed and pulling becomes easier.

  • Temperature

    It cushions thermal shocks (heat spikes, light frost) and limits surface capping after heavy rain.

Watch out for

  • • A layer that is too thick and always damp can favour slugs or rodents on some crops.
  • • A mulch very rich in carbon (RCW, wood chips) suddenly incorporated into the soil causes temporary nitrogen hunger if you do not compensate.
  • • Fresh clippings in a compact layer ferment and heat up: spread them in thin layers or pre-dried.

Examples

  • • Straw
  • • RCW (ramial chipped wood)
  • • Dried grass clippings
  • • Dead leaves
  • • Hay
  • • Coarse compost

Sources

  • RHS (Royal Horticultural Society) : Mulches and mulching (rhs.org.uk/soil-composts-mulches/mulch)
  • Allen, R.G., Pereira, L.S., Raes, D. & Smith, M. (1998). Crop evapotranspiration: guidelines for computing crop water requirements. FAO Irrigation and Drainage Paper 56. Rome : FAO.
  • Barthès, B.G., Manlay, R.J. & Porte, O. (2010). Effets de l'apport de bois raméal sur la plante et le sol : une revue des résultats expérimentaux. Cahiers Agricultures, 19(4), 280-287.