Mulching is the spreading of matter onto the soil surface so as to suppress weeds (and ultimately provide a food source for the plant) by preventing light from reaching the young weeds. Types of mulches include; black polythene, straw, grass clippings, paper, tree bark, wood (not coniferous) chips, marc, timber milling, sugar refining & household waste.

‘Strategic’ mulching can be used to:

  • Reduce variability in the establishment of young vines by apply mulches with a high C:N ratio (straw, paper, woodchip) on more vigorous plants
  • Materials with higher nutrient components (manures, mushroom compost) can benefit sections of poor growth
  • Deeper mulches reduce soil moisture in wetter months
  • Organic materials that encourage earthworms can assist drainage in waterlogged areas (don’t use fresh manures).

Optimal depth depends on properties of mulch material and site characteristics. Most compost mulches are used at a thickness of between 50 & 100 mm. Organic mulches need to be topped up each year.Mulches can be used in the alley or under the row.

Advantages & disadvantages to using mulching

Advantages Disadvantages
  • Effective if spread thickly enough
  • Conserves water- reduces soil water evaporation and increases water infiltration (good for dry climates)
  • Increased earthworm activity and surface soil microbial activity
  • Improves soil structure
  • Reduces erosion (except plastic)
  • Reduces soil temperature variation: limits heat loss from soil at night & reduces maximum soil temperature
  • Protects roots from cold
  • Increased vigour & yield with little change in quality
  • Expensive to spread
  • Encourages superficial rooting
  • Can promote high vigour
  • Increases frost risk
  • Risk of nitrogen deficit
  • Possible increase in fire risk
  • Possible pest infestation