Mulch covers the surface of the soil and is an essential component of waterwise landscaping. Mulching can significantly reduce moisture loss.
There is much debate about materials for mulching, but a waterwise mulch must be coarse and non-absorbent to allow water to penetrate through to the soil, rather than be absorbed by the mulch. Look for mulches that have the Water Corporation’s Waterwise Approved logo.
Ideally the mulch should be long lasting and inhospitable to weeds, containing little nutrient and water holding capacity.
Products such as compost, lucernes and manures should be considered fertilisers/soils improvers rather than mulches.
Mulch is essential when installing drip irrigation as it conceals the drip line. Health regulations state that mulching over dripline for greywater should be to 100mm depth.
Benefits of mulch
- Significantly reduces evaporation.
- Allows water to percolate slowly through to soil rather than run off.
- Reduces radiant heat.
- Deters weeds which compete with plants for water and nutrients.
- Reduces evaporation.
Organic mulches
Pinebark, chipped green waste and other
high carbon mulches are useful as they:
- Have large particles.
- Are non-absorbent.
- Allow rapid water penetration.
- Are long lasting.
- Are not hospitable to weeds.
Inorganic mulches
Inorganic mulches consist of gravels,
pebbles, shell grit etc.
The benefits of inorganic mulch are:
- Does not break down so that although initial cost is higher there is no replacement cost.
- Does not absorb any water so all water percolates through to the soil.
- Has good insulation properties providing a cool root run when laid to sufficient depth.
Applying mulch
A minimum of 50mm of coarse organic mulch should be laid over existing soil surface and 40mm of inorganic mulch (preferably over weed mat). Care should be taken to keep mulch away from the base of the plant to allow airflow and prevent disease.
Mulching slopes
When mulching steep slopes biodegradable jute matting may be required to prevent erosion and run off. Planting and water management on steep slopes may require a range of techniques such as brush mattressing, erosion control matting, bank reshaping and terracing.
Design tips
There are a large variety of decorative gravels, pebbles etc available now which can create interesting
effects in landscapes.
Modern geometric patterns can be very striking where different materials are used for contrast.
Or naturalistic effects can be achieved using materials local to an area – such as the limestone rubble mulch used at
the Pinnacle Discovery Centre.
