Each
year, nature provides a blanket of mulch. While the leaves of deciduous
trees are a fairly obvious ground covering
each fall,
there
are many other natural “mulches”. Evergreen needles are
also shed yearly. Grasses die back and their debris, along with that
of perennials and annuals, cover the ground only to be replaced by
fresh growth in the spring.
This layer of mulch has many functions. It serves to suppress weeds,
retain moisture, moderate the temperature of the soil, reduce compaction,
decrease competition from other plants, improve soil structure, and
provide nutrients to the soil. In our home gardens we remove debris
in order to maintain an aesthetically pleasing appearance. However,
this layer of organic matter is an important component in our gardens
and can be left in place or replaced with organic mulch.
Suppressing Weeds
A five to eight centimetre (two to three inch) layer of mulch will
prevent light from reaching the soil surface. This will stop small
weeds
from emerging and prevent weed seeds from germinating. Weeds that
germinate on the surface of the mulch are easily removed by hand.
Some weeds, such as dandelions and thistles, have enough energy in
their roots to push through a layer of mulch. Ensure these types
of weeds are removed entirely before placing mulch on a bed.
Retaining Moisture
Applying mulch to a bed is an effective way to conserve water. It acts
as a barrier reducing evaporation from the soil surface. Research
indicates that two inches of bark reduce moisture loss in summer
by 21 per cent.* Due to its structure, mulch will also assist with
the infiltration of water into the soil thereby helping to prevent
run off and splashing of water during heavy rain.
Moderating Soil Temperature
Tiny root hairs are necessary for the absorption of moisture and nutrients.
By preventing extreme daily fluctuations in soil temperature, mulch protects
these sensitive root hairs from injury in the heat of the day. In the fall,
a layer of mulch will help to retain ground heat that has penetrated deep
into the soil, which will encourage root growth longer into the season.
Reduce Compaction
Foot traffic in a garden will cause compaction around the root zones of plants.
This reduces growth by limiting air exchange, water infiltration, and percolation.
As the air pockets in the soil are compressed the water holding capacity
of the soil is also reduced. Water will pool at the soil surface, further
preventing air exchange. Compacted soil also makes root extension very difficult.
A layer of mulch helps to reduce compaction by limiting the need for foot
traffic due to a decreased need for weeding and by absorbing some of the
compaction.
Reduce Competition
It’s beneficial to place a ring of mulch around newly planted
trees or shrubs. Turf and weeds compete with plants, robbing them of
nutrients and water. In order to be effective, ensure the mulch ring
is between five and eight cm thick and roughly the size of the root
system below it. It takes three to seven years for a plant to become
fully established. Reducing the competition around the plant will accelerate
this process. Continue to increase the size of the mulch ring each
year until the plant is well established. A mulch ring around a tree
or shrub will also prevent damage caused by lawn mowers and trimmers.
Improves Soil Structure
As organic matter decomposes it turns into humus. Humus acts like glue, holding
together soil particles to create crumbs. The formation of crumbs improves
soil structure. Improved soil structure allows for proper air exchange, water
infiltration, and percolation.
Provide
Nutrients to the Soil
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| Image: A. Neilson |
When mulch is placed in the garden it continues to decompose. As
microorganisms break down the organic matter, essential plant nutrients
are released
into the soil. However, some materials actually rob the soil of nitrogen
as it decomposes. Microorganisms in the soil use up nitrogen as they
consume the carbon in the organic material. As a result, nearby plants
suffer from nitrogen deficiency. This deficiency is temporary. When
the mulch has fully decomposed the nutrients are released back into
the soil. Adding partially decomposed mulch and additional nitrogen
fertilizer can prevent this condition. Grass clippings, blood meal,
or poultry manure can provide the additional nitrogen required. Applying Mulch
When placing mulch in your garden it is important to consider the texture
of both the soil and the mulch. If a layer of mulch is too thick
it may prevent air and water from reaching the soil. Air and water
are important both to the roots of the plant and the microorganisms
found within the soil. Heavy clay soils are not well aerated due
to the small amount of pore space. Coarse mulch should be placed
on clay soils in a layer no thicker than five cm. Sandy loam soils
have larger pore spaces that allow for more aeration. A thicker layer
of mulch with a fine texture can be added to a depth of eight cm.
Soil with a layer of mulch on top takes longer to warm in the spring. The layer
of mulch also prevents water from evaporating. When adding mulch to a bed,
wait until the soil temperature increases.
It is
important not to place mulch against the base of trees, shrubs, or
herbaceous plants. Mulch can provide
a home for rodents that may chew on the base of plants
causing severe damage and even killing the plant. Also, mulch retains moisture
and heat, which will damage the base of the plant. Keep mulch 15 cm away
from the base to prevent any problems.
Mulch
decomposes as it ages; therefore it will need to be replenished from
time to time. How often
will depend on the type of mulch being used. Try
to keep the layer five to eight cm thick throughout the season. Organic Mulches
| Bark |
Bark
provides an attractive type of mulch with good longevity. If bark
is not partially decomposed it may cause a nitrogen deficiency.
Some species of trees, such as hardwoods, have bark that decomposes
much slower than other species. Bark is relatively inexpensive
and can be purchased in bags or by the yard from most garden centres
or landscape supply companies. Bark is effective in reducing compaction
and is not easily blown by the wind.
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| Pine
Needles |
Pine
needles are attractive, resist compaction, and decompose slowly.
They are not readily available for purchase, however they
can be taken from beneath pines found on your own property at no
cost. Pine needles will acidify the soil in time. However, this
is a long process if the soil in your area is naturally
alkaline. |
Wood Chips |
Both
fine and coarse textured wood chips can be purchased. Fine textured
mulches decompose at a greater rate. More frequent applications
will be required. Coarse textured mulches may be considered less
aesthetically pleasing. Wood chips can be obtained from municipalities
for little or no cost. It may also be necessary to provide additional
nitrogen in order to prevent depletion in the soil. |
| Shredded
Leaves |
Leaves
have a pleasing appearance. They can be shredded with a composting
mower or lawn mower and added to the garden. Shredded leaves decompose
quickly and must be replenished regularly. They are available at
no cost. Leaves may cause a nitrogen deficiency. Whole leaves should
not be added. They tend to mat and block water from infiltrating
the soil. Well-rotted leaf mulch is perhaps the best mulch, providing
nutrients as it breaks down into beneficial humus. |
| Straw |
Straw
has a course appearance that may be undesirable for some. It will
require frequent applications. Straw is inexpensive mulch that
is ideal in vegetable gardens. While it provides the benefits of
other mulches it also keeps the fruits and vegetables clean. Nitrogen
should be added to prevent depletion of this nutrient. Straw may
carry weed seeds. |
In the long run, mulching your flower and vegetable beds can save
you a lot of time. It can drastically reduce the amount of time you
spend weeding and watering. It also looks good and prevents soil from
splashing onto your flowers when it rains.
· Research by the Weyerhaeuser Co. (1969)
Ohio State University Extension Fact Sheet www.growinglifestyle.com/article/s0/a12550.html
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