HomeMy WebLinkAbout2024-06-04-TREE-att-copy (4)RESEARCH LABORATORY TECHNICAL REPORT
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Root Pruning Kelby Fite, PhD, Plant & Environmental Science
& E. Thomas Smiley, PhD, Urban Forestry
Root pruning is the process of cutting roots prior to mechanical excavation near a tree. Root pruning may be
necessary to minimize damage to the tree’s root system during construction or in preparation for large tree
transplanting. Improper root pruning and root damage from excavation can cause great harm to a tree which may
affect tree health and/or structural stability. A tree risk assessment should be performed prior to cutting any roots
and alternative techniques, such as boring under the roots, should be considered.
Root Pruning Methods
When pruning roots, there are guidelines regarding
size: roots less than one inch (2.5 cm) in diameter can
easily be cut with hand tools while cutting roots greater
than three inches (7.5cm) in diameter should be
avoided whenever possible. There are three general
methods of root pruning in the one- to three-inch
diameter range:
Air/Water/Hand Excavation and Pruning
Excavating roots requires the use of the AirSpade®,
hydro excavation or hand tools. This exposure allows
the arborist to evaluate the best places to cut,
preferably beyond sinker roots or junctions. Roots can
be cut most cleanly with a sharp saw or lopper.
Exposed fine roots that are to be preserved may be
covered with burlap and sprayed with water, or they
can be sprayed with a hydrated, fine, water-holding gel
to prevent desiccation.
Root-cutting Machinery
A root pruner, such as the Dosko or Vermeer Root
Pruner, is faster than the previous method (Figure 1).
These tools have teeth similar to a stump grinder and
provide relatively clean root cuts. However, this
method does not allow for the arborist to evaluate the
exact location of the pruning cuts and will, likewise,
be indiscriminate.
A chain trencher or excavator is one of the worst ways
to prune roots because they often lift surface roots out
of the soil until they break and leave other roots
crushed or torn. After using a trencher, it is better to
prune the damaged ends by hand than to leave them
untreated. Sometimes, due to site constraints,
trenchers are the only option due to their flexibility.
Root Cut Placement
The further from the trunk that root cutting occurs,
the better, but generally root cuts made outside a
normal dripline of a tree rarely cause permanent tree
damage. The preferred minimum distance from the
trunk to the closest root cut is 5 to 6 times the DBH.
Figure 1: A root pruner in action
Trencher or Excavator
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For example, with a 12-inch (30 cm) diameter tree, the
root cut distance should be 60 to 72 inches (5 to 6 feet,
1.5 to 1.8 m). At this distance, there should be minimal
impact on the health or stability of most tree species
with proper aftercare.
For root cuts on only one side of a tree, the root cut
distance can be somewhat closer to the trunk than cuts
on more than one side. The preferred minimum
distance in this case is three times the DBH. For
example, with a 12-inch (30 cm) diameter tree, the
distance would be 36 inches (3 feet, 0.9m) (Figure 2).
This distance is too close if there is pavement over the
other side of the root system, if the tree has root decay,
is leaning or has other indications of root disturbance.
These trees also need proper aftercare to reduce the
risk of health problems.
Figure 2: General guidelines for locating root
pruning cuts
In all cases, consider variables such as tree species, age,
tree health, and soil characteristics (including the
presence of underground root obstructions) when
determining location of root pruning. Cuts made
closer to the trunk may dramatically compromise
stability and health and should be avoided.
Plant Health Care Before and After Root Pruning
Tree health and soil moisture should be monitored
frequently following root pruning. Root pruning
should not be done immediately prior to or during a
drought period unless the tree will have adequate
irrigation. Irrigation should be applied prior to and
after root pruning if there is not adequate rainfall.
Monitor for secondary pests and apply protective
treatments to susceptible trees for lethal invaders such
as borers. Fertilizer and soil amendments should be
applied according to soil or foliar nutrient analysis test
results. Bartlett's Root Invigoration should be
performed to promote root regeneration and a
better environment for remaining roots. At a
minimum, mulch should be applied to reduce soil
moisture loss and promote root growth.
Founded in 1926, The Bartlett Tree Research
Laboratories is the research wing of Bartlett Tree
Experts. Scientists here develop guidelines for all of
the Company’s services. The Lab also houses a state-
of-the-art plant diagnostic clinic and provides vital
technical support to Bartlett arborists and field staff