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 that these types of
weeds are removed entirely before placing mulch on a bed.
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 five centimetres of bark reduce moisture loss in summer
by 21 percent. 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.
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.
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
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. Ensure that the mulch ring is between five and eight
centimetres 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.
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.
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 they decompose. 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