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My soil is well mulched but is water-repellant to rain and irrigation PDF Print E-mail

Mulching soil is essential because it conserves moisture, insulates surface feeding plant roots from extremes of heat and cold, supplements the organic matter content of soil whilst reducing the risk of soil erosion. Mulching can also help suppress diseases.

Mulch that is too thick can prevent rain and irrigation from penetrating the soil. A 10-15cm deep layer is sufficient for established trees and shrubs. A 5-10cm deep layer is suitable for larger perennials and a 1-5cm deep layer is suitable for annuals, smaller herbs and vegetables.

Repetitive use of the same type of mulch made from one type of plant, such as pine bark mulch, tends to stimulate the growth of a limited range of fungi. These produce fine networks of white fungal threads, known as hyphae, which digest the mulch. They occur just below the surface and these threads can gradually bind mulches into a solid mass and this can become water repellant.

As a general rule:

  • Hard, woody, carbon-rich materials, like pine bark, eucalyptus bark and tea tree mulch mostly benefit fungi;
  • Soft, leafy, nitrogen-rich materials, like lawn clippings, vegetable scraps, sugar cane, lucerne and straw mostly benefit bacteria;

Organic rich soil is healthy and brimming with life - a single teaspoonful of biologically active soil can contain up to 20,000 different species of micro-organism. Many of these life forms don’t have scientific names but the wonderful thing about them is that most are harmless and many are beneficial. Using the right types of mulch and applying appropriate depths feeds beneficial soil micro-organisms - the ‘good guys’ - that actively help suppress many soilborne diseases.

By varying the types of mulch you use each time you stimulate different types of soil micro-organisms. That’s why compost made from a balanced range of materials is very beneficial to the widest range of micro-organisms.

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