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Mulch - What is it?

Material placed on soil to cover and protect it is called mulch.

Types of mulch

There are two types: 

  • Organic mulches which include bark, wood chips, leaves, lawn clippings, straw, paper and other organic by products.
  • Inorganic mulches include crushed stone, asphalt and concrete.
Covering the soil with plastic materials

Often the soil is covered with polythene or a geotextile fabric [ weed mat ] and then its covered with an organic or inorganic product.

Benefits of mulch
  • Soil moisture is conserved
  • Soil erosion and water loss are reduced
  • Soil fertility is usually increased
  • Weed competition is reduced
  • Soil structure is improved
  • Soil compaction is reduced
  • Soil microbial activity increases
  • Soil temperature is moderated
Problems caused by mulch
  • Insufficient water and air is a problem under plastic
  • Nitrogen deficiency may occur especially in wood chips and bark. To counter act this it may be necessary to add extra nitrogen to the soil
  • Some diseases and pest may be more serious especially if there is excessive moisture. Keep an eye open for slugs!
  • Some mulches are toxic these include: fresh lawn clippings, eucalyptus wood chips and leaves, redwood and cedar wood chips, douglas fir, larch and spruce bark.
  • Toxic substances can be removed by correct composting.
Mulch research
  • In trials carried out in North America comparing various mulching compounds including: fibre glass, hay, bark, plastic and wood chips, the latter were found the most effective material particularly for retaining soil moisture.
Mulch application
  • Do not pile mulch against the stem of trees this provides an ideal environment for, causing collar rot.
  • Apply about 100mm [ 4 inches ], any deeper could have adverse effects on soil properties.
  • If using black plastic or geotextiles make sure the soil slopes away from the plants for drainage, and prick the plastic to provide holes for air and water.
  • Up grade wood chip or bark mulch every few years as it will slowly break down.
  • If growth is vigorous and the leaf colour dark no fertiliser is required.
  • If leaves are yellow and growth slow a light application of a slow release nitrogen fertiliser should be broad cast.
  • Mulching is very important to woody plants not only does it look good , and reduces maintenance, but produces a healthy plant.
  • It will stop damage to bark and roots from lawn mowers and string trimmers.
  • Mulching will mean that you will not have to use herbicides to control weeds.