Root
and Soil Invigoration
Soil compaction, improper mulching, and trunk flare disorders
can prevent woody plants from flourishing and lead to
premature death of established trees. We use a variety
of the latest tools and tactics to help solve these landscape
issues.
Soil Compaction
Healthy soil is a composite of mineral particles, organic
matter, water, and air. It also contains a "living element"
that includes thousands of species of bacteria, fungi,
insects, and worms. This living element is responsible
for breaking down the organic matter in the soil, releasing
the trapped nutrients that nourish plants. Soil microbes
and the tree roots that they "feed" require adequate moisture
and air for optimum growth and development. Construction
equipment, vehicular and pedestrian traffic, and even
lawnmower use can compact the soil structure resulting
in sterile, droughty soils that can't support healthy
microbial populations.
Aerating the soil and incorporating additional organic
matter in the form of compost can restore vitality to
the soil and the tree roots that are living in it.
Mulching
The many benefits of landscape mulch are well documented:
- Weed suppression
- Moisture retention
- Soil temperature moderation
- Aesthetics
The bark mulch phenomenon Of the dozens
of different types of mulch available, coniferous bark
mulch is by far the most widely used in our area. Bark
mulch is an abundant by-product of the timber industry,
and over the last twenty years it has become the most
common landscape mulch product in both commercial and
residential settings.
Much of tree bark is made up of cork cells that contain
a natural waxy substance called suberin. This substance
is very resistant to decay and as a result, bark mulch
is relatively slow to break down. With repeated applications,
this material tends to build up, trapping moisture against
the base of the tree, reducing air flow to the stem
and roots, and increasing the occurrence of root-rot
fungi. Also, these cells are essentially "dead" so even
when they do break down they don't offer much nutrition
for the soil organisms, or ultimately, the plants. As
a soil conditioner, bark mulch has very little to offer.
Learning from nature Most ornamental
woody plants used in the landscape are native to woodland
settings. In the forest tree roots are covered by a
thick layer of decaying leaves, twigs, and branches.
Within the structure of the tree system, the highest
concentration of essential plant nutrients (N, P, K,
Ca, Mg) exist in the fine branches and twigs which litter
the forest floor. This thick layer of nutrient-rich
humus is what supports the growth of large trees in
areas where the native topsoil may only be a few inches
thick and/or of very low fertility. In order to simulate
this natural humic layer, we recommend mulching with
a seasoned, chipped branch-wood material that we call
our "Forest Floor Mix". The advantages of this material
include:
- Attractive, naturalistic appearance
- Conserves moisture without "suffocating" the soil
- Breaks down gradually adding valuable organic matter
to the soil
- Less expensive than bark mulch
Trunk Flare Disorders:
The result of trunk flare disorders are all too familiar
— foliar yellowing, early leaf discoloration and
drop, dieback of twigs and branches of the upper crown
and, eventually, tree mortality caused by secondary
invaders (pathogenic fungi, insect borers and others)
that are attracted to stressed plants.
What is the Trunk Flare?
The term Trunk
Flare describes the region of the tree stem where
the trunk tissues differentiate into root tissues. The
tissues in this area are specialized and critical to
the whole tree system. The proper conduction of water
and food materials and the mechanical support of the
entire tree structure depends on a sound, healthy trunk
flare area.
The most common cause of trunk flare disorder is burial
by soil or mulch. This occurs when trees and shrubs
are planted too deeply or settle after transplanting,
when soil is added around the plant base during landscaping
or when mulch is piled against the trunk. Another common
cause is physical damage from lawn mowers, string trimmers,
vehicles or gnawing by small animals. Many young trees
struggle to establish or die due to injury or burying
of the trunk flare area.
Recent research is also exposing the prevalence of
Girdling Roots on trees with buried trunk flares.
Growth of these adventitious roots is stimulated by
the abundant moisture in the fill material and by modern
nursery growing and harvesting techniques. Frequently
they encircle the trunk flare and eventually begin
to constrict trunk growth. In severe cases it can result
in decline, death and even whole tree failure as the
plant is unable to develop adequate conductive and
structural support tissues.
Remedying the Situation In many cases,
particularly with young specimens, a trunk flare excavation
can help reverse the decline symptoms. This is best
performed by an experienced arborist and involves the
careful removal of excess soil or fill material from
the base of the tree.
This can be achieved with hand tools, or with the use
of a specialized tool called an Air
SpadeŽ or an Air KnifeŽ. These tools use highly
compressed air to blow away excess soil and mulch without
damaging the tree trunk or roots. When Stem Girdling
Roots are discovered, the arborist must determine weather
or not root surgery is practical and appropriate.
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