Debunking a Tree Planting Myth:
Fall Transplant Hazards
Story
Story and
and photos
photos by
by Matthew
Matthew Stephens,
Stephens, Director
Director of
of Street
Street Tree
Tree Planting
Planting for
for the
the City
City of
of New
New York
York
Department
Department of
of Parks
Parks &
& Recreation
Recreation
B&B trees dug properly—i.e., when dormant.
Some trees are simply more difficult
to transplant
than others. Furthermore, when trees are harvested and/or
stored improperly, the likelihood of tree mortality increases.
Complicating the issue is the fact that it is difficult to trace tree
mortality back to one finite reason. Tree mortality is a tapestry
of interrelated issues that compound and result in tree death.
One facet of transplanting around which there has been much
confusion is fall harvesting of B&B trees. There has been some
reluctance among the nursery and landscape industry to dig
certain species of trees in the fall, but this “fall hazard list” varies among nurserymen. This reluctance is not unwarranted, but
when certain precautions are taken, tree harvesting of all species
may occur in the fall.
B&B tree harvesting is in itself a miraculous feat. Research
suggests that as little as two to eight percent of roots actually
accompany a tree once it has been harvested in the root ball.
Furthermore, as tree caliper increases, so does the amount of
time needed to reestablish a balance in the root:shoot ratio, but
with appropriate soil moisture and enough time, transplanted
trees will reproduce their root mass.
These hedge maples (Acer campestre) were dug too early.
Trees with a more fibrous root architecture regenerate more
rapidly than trees with a more prominent tap root. Additionally,
research has suggested that most root growth slows significantly
once soil temperatures reach 50 degrees F (10° C) and winter
dormancy approaches. When trees are harvested between late
fall and early spring, root elongation virtually ceases. Therefore,
1. Harvest at the Right Time
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if the tree’s root system is essentially static, it should make no
difference if a tree is harvested in the fall or early spring. There
must be other variables at work that ensure success of a transplant. The following list considers four major factors for a successful tree harvest and transplant.
During the fall, trees reach dormancy at different rates/on different
schedules. One reason that some trees have been thought to be fall
dig hazards (see table) is that they have been harvested too early.
Some trees go dormant very late in the fall depending on weather
patterns, and if the weather turns cold quickly, growers will not
City Trees
Tree Species Presumed to be Fall Hazards
Common Fall Hazard Traits
Trees with
Minimize
Moisture Thin Barked Harvest Coarse
Trees
Loss
Time
Roots
Acer rubrum
X
X
Betula sp.
X
X
X
Carpinus sp.
X
X
X
Celtis sp.
X
X
Cercis sp.
X
X
This B&B tree was shipped so dry that sandy soil poured out of
the rootball when the burlap sustained a small tear.
Cercidiphyllum japonicum
X
X
Cornus sp.
X
X
have the time or capability to dig the trees before it becomes too
cold or the growing fields become inaccessible to machinery.
Crataegus sp.
X
Fagus sp.
X
Halesia sp.
X
X
Liquidambar
styraciflua
X
X
Liriodendron tulipifera
X
X
Malus sp.
X
X
Nyssa sylvatica
X
Ostrya virginiana
X
X
Platanus sp.
X
X
Pyrus sp.
X
Quercus sp.
X
Taxodium distichum
X
Tilia tomentosa
X
X
Zelkova serrata
X
X
A perfect example of this can be seen with the genus Quercus,
which goes dormant extremely late in the fall. A possible solution is to strategically procure trees from distinctly different
climates. For example, if Quercus were on a planting plan in
the fall, it would be wise to obtain trees from a reasonable
northern source where there is an earlier digging season, thus
making the trees available weeks ahead of locally grown trees.
Regardless, it is absolutely critical to ensure that trees are harvested in a dormant state.
2. Root Prune Coarse-Rooted Trees
Some trees that have been labeled fall hazards have coarse root
systems that regenerate more slowly. The genus Nyssa has a
tap-root-like root architecture when compared to Metasequoia,
which has a much more fibrous root system. Research indicates
that the roots of Quercus coccinea require approximately three to
four times longer to regenerate than those of Q. palustris.
Also, if a tree with coarse roots is harvested in the fall and
a harsh winter comes along, freezing the soil early and
consistently, the tree becomes more easily desiccated due
to an inability to replenish water. Therefore, any coarsely
rooted tree should be prepared for digging in the fall by
root pruning the previous spring. Careful root pruning in
the beginning of the growing season forces a more fibrous
root system by fall harvest time. For example, a 2.0- to 2.25inch (51-57 mm) caliper tree could be prepared in spring by
spading two or three sides of the root system as if it were
going to be placed in a 28-inch (71 cm) root ball. It would
be left in ground and allowed to grow until fall harvest, at
which time the tree would be spaded and placed in a 32inch (81 cm) root ball.
3. Harvest Thin-Barked Trees with Abundant Twigs
with Special Care
Deciduous trees desiccate during dormancy due to cold, wind,
or sun, especially when the ground is frozen. This problem
is compounded in trees that have thinner bark because there
is more cambial activity on sunny days for thin-barked trees.
Desiccation is also more likely on trees with abundant twigs
www.urban-forestry.com
X
X
X
X
X
X
X
X
X
X
X
X
X
because there is an increased surface area exposed to potential
inclement conditions.
Ensure that vulnerable tree types get harvested in the right size
root ball or one size larger in an effort to retain as large a root
mass as possible. A larger root mass translates to a larger amount
of available moisture contained within a tree. Additionally, trees
with thin bark and abundant twigs should be watered during
the winter season when there are extreme cold, windy, or sunny
conditions.
4. Minimize Water Loss to Root Balls
After harvesting, trees need a constant source of water, especially when they are stored above ground. The outer layer of
burlap around the root ball will wick water out of the encased
soil during dry, windy, or sunny days. Make sure that trees are
well watered until they are planted in the ground. Letting the
root ball dry significantly even one time can cause tree mortality
or make it virtually impossible to restore moisture to the core of
the root mass. Depending on the weather conditions, it might
be necessary to water an aboveground tree with a slow soaking
for at least five minutes per day. Additional precaution could be
taken by heeling the trees in mulch.
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