3. Good Organic Gardening - May-June 2016 AvxHome.in

Mulch | WEEKEND GARDENING
Leaf litter makes good mulch
Words Jennifer Stackhouse
Mulches keep soil cool on
hot days, suppress weeds,
protect soil from damage
from heavy rains, reduce
water loss and, as organic mulches break
down, add nutrients to the soil.
Many gardeners believe that the deeper
the mulch layer, the better. But, while deep
mulches may suppress weeds and add
organic matter as they break down, it appears
that deep layers of mulch can lead to soil
problems, especially in times of low rainfall.
Too much mulch
Soil expert Kevin Handreck has conducted
studies into mulches. His research has
revealed that deep applications of fine, waterabsorbing
mulches inhibit water reaching
the soil and contribute to water repellency
in soils. In cottage-style and permaculture
gardens, deep mulching also inhibits selfseeding
of annuals and perennials.
In his book Good Gardens with Less
Water, Kevin explains that fine mulches,
especially where they include an added
wetting agent, hold water. If there isn’t much
water falling on the garden, the mulch may
stop water reaching the soil and hydrating
the plants. Mulches with high levels of dust
can also absorb moisture and prevent it
reaching the soil.
“A 100mm-thick layer of fine mulch with
a wetting agent added to it could trap up
to 60mm of rain or sprinkler water before
any water reaches the soil,” Kevin explains.
“Mulches with high proportions (greater than
80 per cent) of particles larger than 5mm are
best at letting rain reach the soil.”
He also warns that increasing the depth
of coarse mulches above 35mm has no
benefit in reducing water loss. The best
coarse mulches reduce water loss by up
to 63 per cent.
These findings have led Kevin to
recommend using a 5–10mm layer of fine
mulch overlaid by a 35mm layer of coarse
mulch as the best mulching regime for
gardens. Total mulching layers should not be
greater than 50mm in depth. The fine mulch
could be compost or well-rotted manure,
which breaks down to feed the soil.
Natural systems
Kevin also recommends using mulches that
best reflect the natural growing conditions
of the plants that are being mulched. For
example, cacti and succulents grow naturally
in sandy and rocky areas so are best mulched
with inorganic mulches.
Native woodland plants (including many
vegetables) grow amid a natural mulch of
fallen leaves and bark and so do best with
coarse, organic mulches. This type of mulch
also improves the beneficial bacteria and other
organisms in the soil.
To read more of Kevin’s mulching
recommendations, visit books.google.com.au
and search for mulches.
Selecting
the best mulch
There are many coarse, water-repellent
mulching products. Chopped or shredded
bark, green prunings and gravel all fit the bill.
For an organic gardener, it’s important
to select and use mulches that are free
of contaminants, including pesticides and
Prunings can
be mulched
... deep applications of
fine, water-absorbing
mulches inhibit water
reaching the soil and
contribute to water
repellency in soils ...
deep mulching also
inhibits self-seeding
of annuals and
perennials.
Good Organic Gardening | 39