The addition of mulch can give a landscape a fresh
look while providing numerous benefits to plants.
However, too much mulch can have a detrimental effect
on trees and plants. It is not uncommon to see mountains
of mulch piled against tree trunks. We call these
excessive piles ‘volcanoes’, and they
are not a good thing. Excessive mulch can actually
smother root systems and create environments that
inhibit growth.
The lower-most portion of trunk, or root collar, is
composed of specialized cells which are not adapted
to resist constant soil moisture. When excessive mulch
or soil is piled against the root collar and trunk,
it can inhibit the necessary exchange of oxygen and
interfere with the downward movement of food to the
roots. This eventually leads to root dieback, reduced
water uptake, and ultimately, tree death. In addition,
excessive mulch encourages shallow root systems.
Too much mulch reduces oxygen availability, causing
roots deeper in the soil to die. Shallow root systems,
lead to stress during drought periods. Secondary pathogens
are then able to attack these weakened trees. Most
plants benefit from only a 2-3 inch layer of composted,
organic-matter mulch. As mulch slowly decomposes over
time, microbial activity increases, creating beneficial
soil conditions which, in turn, release nutrients.
When applied properly, mulch also protects the base
of trees from weed whacker damage and reduces resource
competition with turf grass and weeds. In addition,
mulch tends to stabilize soil temperatures and increase
soil water holding capacity, which conserves moisture
during drought conditions, thereby minimizing water
use.
Be cautious of inorganic materials, including black
plastic. Plastic may discourage weeds, but can also
interfere with normal gas exchange of the roots. Plastic
also contributes to the development of shallow root
systems.
Clearly, the proper mulch and method of application
can directly improve the health and vitality of landscape
plants. To determine if your planting beds or trees
are properly mulched, inspect the plant material and
soil conditions of the area. If mulch is present, check
the depth. Where mulch is piled against the stems or
tree trunks, pull it back away several inches. Do not
add mulch if there is already a sufficient layer. Simply
raking old mulch to break up matted layers may be enough
to refresh its appearance. Hartney Greymont introduced
our own mulch last year called ‘Yard Life’ mulch. ‘Yard
Life’ is a blend of aged and composted tree residue
by-products. Research has shown this mulch closely
matches the organic layer of the forest, creating a
rich, rooting environment for trees and shrubs, resulting
in healthy, vital plants and soil. Judging from the
demand for this new product, our clients have noticed
the results in their landscape too.
