How to mulch

This week we look at materials to use as organic mulch and the advantages and disadvantages of each.

How to mulch
Using shredded bark as mulch is good because it allows water in the soil and keeps it there for a while. But it’s quite expensive.
Photo: Peter Mashala
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Wood chips

Best when applied in a layer 50mm to 100mm thick.

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Advantages

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  • Absorbent and lets water in effectively.
  • Cools soil and controls weeds.
  • Many wood types and particle sizes are available, but avoid large chips.

Disadvantages

  • Decomposes in a year or two, depending on the wood and particle size.
  • Small particles require nitrogen as they decompose quickly.

Sawdust

Best when applied in a layer 20mm to 75mm thick.

Advantages

  • It’s good for soil that’s easily waterlogged, as it lets water in slowly, absorbs a great deal, and not all the water reaches the soil.
  • Increases the water-holding capacity of soil as it disintegrates, and forms a barrier that compacts in time.

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Disadvantages

  • Breaks down rapidly.
  • Blows in the wind when it’s dry, and crusts.
  • Regionally available.
  • Needs nitrogen added to the soil or to the sawdust to avoid nitrogen depletion.
  • Some wood types disintegrate slower.

Shredded bark

Best when placed in a layer 50mm to 100mm thick.

Advantages

  • Binds the soil.
  • Lets water in, holds it in the soil well and builds the moisture-holding capacity of soil.
  • Looser than wood chips and more open than sawdust.

Disadvantages

  • Expensive.
  • May compact in time.
  • Can be unsightly and ineffective if applied too thinly.

Chunk bark

Best when applied in a layer 20mm to 50mm thick.

Advantages

  • Because it has a coarse texture and large particles, it lets more water in.
  • Long lasting.
  • Allows water to pass through the mulch layer.

Disadvantages

  • Fairly expensive.
  • Regionally available.
  • Breaks down slowly, so it doesn’t improve soil texture.

Source: Water Wise by Rand Water