Mulching your garden


Mulching is a wonderful way to improve soil
condition. Mulch reduces soil water loss,
keeps soils cooler in summer, and helps to
reduce the number of weed problems in your

Why we use mulches

Mulching is the single most important thing
you can do to help your garden survive in our
dry climate.

Mulches reduce evaporation

The principle reason for mulching is to
reduce evaporation of water from the soil. In
fact, it has been shown that a 70 mm thick
layer of mulch will reduce soil evaporation by
as much as 70 per cent.

Other benefits of mulching

As well as reduced evaporation, mulching
has a number of other benefits. As the
mulch breaks down it improves the soil’s
structure and its ability to hold moisture in
the root zone of the plant. At the same time
it is adding nutrient to the soil. A mulch will
also reduce the number of weeds, and this
is important as weeds use precious water.
You will also find that any weeds that do
germinate in the mulch are very easy to
remove. Importantly, mulches can prevent or
delay the formation of water repelling crusts
that often form on our soils.

Types of mulches

A mulch cover can be formed from a wide
range of materials. They can be cheap or
expensive and formed from either organic or
inorganic materials. Quick rotting mulches,
such as pea straw and compost, have the
benefit of adding organic matter rapidly,
but need to be replaced regularly. Long
term mulches, while lower in maintenance,
do not give much benefit beyond reducing


Compost is the best mulch you can use as
it has plenty of nutrient, good evaporation
control, and quickly improves soil texture
and water-holding. It is also a great worm
encourager, and it is easy to make your own.

Pea straw or lucerne hay

Both pea straw and lucerne hay have plenty
of nitrogen and break down well to supply
nutrients to plants. They are ideal for heavy
feeders like roses and vegetable gardens,
especially where their quick decay improves
soil texture. Avoid using in very windy areas.

Shredded green waste

Council landfills and private operators often
have shredded green waste for sale at very
reasonable prices. As this material can often
contain weeds or seeds it is essential that
you compost it first before using it as a
mulch or soil improver.

Grass clippings

High in nitrogen content, these are best
mixed with leaf litter, straw or twiggy
material to prevent it forming soggy, water
impenetrable layers. Ideally, it is best to
compost grass clippings before using.

Paper or cardboard

Ideal to use under bark or stone. Paper
should be several layers thick and have holes
punched in it to allow water through. It is
best to wet the paper or cardboard before
laying it.

Bark or wood chip

Some bark and wood products contain
substances that inhibit plant growth, and
should be left for several months in the
weather to leach out toxins prior to using
as a mulch. Most of these products can be
used around established plants. Think about
the source of the material and try to make
environmental choices, like using pine bark
rather than red gum.

Mushroom compost

Mushroom compost is often available. This
has great moisture holding ability and makes
a fantastic soil improver as well as a mulch.
Generally it is weed free, but be aware that
it has lime added to it, and so is no good for
lime sensitive plants such as Camellias.

Stone, pebbles or rocks

Stone, pebbles or rocks are examples of
good long-lasting mulch material, especially
for storing heat through the day and releasing
warmth at night, which is great for frosty
areas. Again, avoid using unsustainable
materials and choose by-products or
recycled materials like crushed bricks.



Better than plastic because it lets air and
moisture through. If using an irrigation system
it is best to have drip irrigation under the


This is best avoided as it reduces available
air for the soil to breathe, often making the
soil turn ‘sour’. While plastic does reduce
evaporation it also sheds water, often
meaning that less water gets into the soil.

Living mulches

Many people use low and ground covering
plants as a living mulch. These probably use
up any water they save, but do create an
interesting and green garden. Make sure you
use plants with low water requirements.

Using mulch

Mulches are essential in our dry climate to
help create a more waterwise garden. Here
are a few tips on their correct use.

How to mulch

Always thoroughly remove any weeds before
mulching. Then give the soil a light forking
over to break up any crust that might have

Organic mulch, particularly long-term ones
such as bark and wood-chips, can develop
nitrogen deficiency in plants, causing them
to turn yellow. This is caused by bacteria
taking nitrogen out of the soil to break down
the organic matter. If using these types of
mulches it is important to add nitrogen to
the soil. Blood and bone or any type of
animal manure is a great way to counter this
problem. Add this after you have broken up
the crust and then give it a water in. Then
put your mulch on top. Mulch should be kept
clear from the stem or trunk of a plant to
prevent collar rot disease, and ring-barking
from frost.





Mulch thickness

The depth of a mulch layer depends on
the material you are using. If it is fine, like
compost, or a mixture with a lot of fine
material in it, such as shredded green waste,
then it needs to be put on thinner, say
30 mm thick. This is because the fine
material holds moisture and reduces the
amount of rain and irrigation that can
get through it. Chunkier and more open
materials, such as pebbles, wood chips and
barks, should be used at around 70 mm
thick. Do not use it any thicker as it will be
too hard for water to get through.

Apply mulch in early summer

As the principal role of mulch is to reduce
evaporation, the best time to mulch is early
summer. The idea is to allow as much winter
and spring rain to enter the soil as possible
before placing the mulch on, to reduce
the loss of that moisture. If you are using
a quick-rotting mulch then this will be an
annual task. Long-term mulches should still
be checked every November, then topped up
if necessary.

Coliban Water

City of Greater Bendigo

Coliban Water

37-45 Bridge Street,
Bendigo VIC
ABN 96 549 082 363