GK MACHINE
The digging scene
The evolution of machines
for B&B and bare-root
production has made field
harvesting more efficient
and cost effective
By Miles McCoy
vested, the results were very different.
The costs were lowest for pot-in-pot
systems and highest for field production. Nonetheless, B&B field harvesting is still used in many specific
industry segments.
Moving to fewer hands
One of the drawbacks of field
production, historically, has been that
it is labor intensive, requiring large
hand crews.
Historically, with balled and burlap
harvests, a root ball was first hand-dug.
Then burlap was pinned and tied tightly
around the root ball. This held the
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For a century, growing in the field
was the only method nurseries had to
produce plants. Then, the use of metal
cans to grow plants first signaled a
change was coming.
Containers — first clay and then
metal cans called “plantainers” — were
used for growing in the early 1950s.
This was followed by increasingly
sophisticated plastic can designs that
quickly took over the industry.
Most statistics put container production at roughly two-thirds of the U.S. total
nursery industry acreage, though contain-
ers account for a higher percentage of
total sales. Accurate cost comparisons
between nursery production systems are
difficult to determine, however, due their
extreme diversity of products.
A 2002 study by the University of
Arkansas looked at the total production
costs for a hypothetical 15-acre nursery with 10 acres in production over a
three-year production cycle. It concluded that the overall costs were lowest for
a field system, and higher for container
and pot-in-pot (PIP) systems. However,
both of these systems accommodate
more plants over the same acreage.
When the figures were computed
on an average basis, per plant har-
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The digging scene
GK MACHINE
The H7 tree digger by GK Machine of Donald, Ore.
will dig trees out with the roots. An attachment is
available (see picture on previous page) to shake
the dirt out of the roots.
soil in place around the roots. To save
on costs, producers started looking to
mechanization and automation of the
digging process.
Over the past few decades,
mechanical digging with a tree spade or
bare-root digger became the standard
harvesting technique. Though some
producers still use hand digging, today
there are several methods that can be
used, depending on the crop, to extract
the plant, root system and surrounding
soil from the ground.
Bare root harvesting utilizes diggers
that under-cut, lift, and shake the young
tree, leaving little soil on its roots.
Growers also may use mechanized
diggers that create a ball of soil around
the roots. This provides some protection while the plant is transported
and transplanted. Tree spades, usually
equipped with three or four hydraulic
blades, extract a cone of soil and roots
which are placed in a wire basket
lined with burlap and secured using
pinning nails and twine.
These diggers and burlap-lined wire
baskets made harvesting nursery stock
in sandy soils more successful. Although
mechanical harvesting is possible in less
cohesive soils, it is still important for soil
to be retained around the roots.
Bare root tree digger design
Bare-root tree diggers also
appeared mid-century in various forms.
Early versions were often modifications
of John Deere equipment, raised and
outfitted with a custom digging mechanism added.
Some mention Princeton Nursery
of Allentown, Pa., as an early innova-
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DIGGER
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tor. That nursery’s bare-root production
took off in the 1950s, after owner Bill
Flemer invented a raised caterpillardigging machine. But, growers such as
John Holman (Pacific Coast Nursery),
Archibald McGill and J. Frank Schmidt
Jr. all developed early models.
Early designs were adjustable,
U-shaped scoops pulled behind a
typical tractor. It was adjusted to travel
under the plant’s deepest root. A shaking grate attached to the rear and a
hydraulic motor dislodged soil as the
tractor moved forward.
Today’s bare-root digging machines
are much larger, designed especially for
this process. Most are huge, U-shaped
pieces of equipment that travel over
tree rows, lifting and shaking trees that
are then gathered by hand crews. They
are built by numerous manufacturers,
including GK Machine in Donald, Ore.
Ball and Burlap Diggers
For decades, the huge, cone-shaped
blades of a tree spade were recognized
as the ultimate choice in moving B&B
stock. They worked relatively well,
reducing labor significantly and controlling transplant shock.
Then in the last few years, a different approach to digging was introduced
when Plant Oregon of Talent, Ore.,
bought one of the first Italian-made
Holmac Diggers, which digs a round
root ball, similar to an ice cream scoop.
They now represent the company in the
United States.
Owner Dan Bish said it dramatically
improved their field digging process. It
uses a rotating, vibrating blade that cuts
under the plant, lifts it and places it on
a wire basket frame covered with burlap. He said the Holmac extracts 30-60
balls per hour, 240 to 480 balls per day.
“This can radically reduce labor
expenses, up to 75 percent,” said Bish.
“The blade vibrates at a very high speed
and easily cuts through the ground.”
An Oregon nursery bought one of
their first machines and it was so suc▲
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The digging scene
CURT KIPP
The Holmac HZC 16-22 tree digger, imported by Plant Oregon, digs field-grown trees for B&B shipment,
taking only as much dirt as the tree needs. Its makers say the treads of the machine are light on the
ground and don’t compact the soil.
cessful the nursery paid for the machine
in three months, he said.
Andy Spinks of Jim Spinks Nursery
in Gresham, Ore., is a fan of this technology. “It eliminates the hassles of
trying to get a digging crew,” he said.
“With the Holmac, each tree costs about
30 cents to dig, and it’s so quick.”
The machines comes in several
models, from the HZC 16-22 at 60 inches long, and a narrow width of 36 inches to the largest machine, the Holmac
HZC 29, 100 inches long, with a 36 to
55 inch width.
GK Machine is also introducing a
digger with similar technology soon,
according to its website.
Research improves digging processes
Research at the University of
Florida (Beeson and Gilman, 1995)
showed that under limited irrigation
conditions, trees from containers died
sooner and more trees died compared
to field-grown B&B trees, while the
root-pruned field-grown B&B trees
survived best.
They did note that if the trees were
irrigated regularly through the first
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SEPTEMBER 2010
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DIGGER
growing season, they all survived. But,
under limited irrigation, landscape managers should plant root-pruned, fieldgrown B&B nursery stock.
Meanwhile, other Florida research
with live oak (Quercus virginiana) and
Chinese elm (Ulmus parvifolia ‘Drake’)
showed that fertilizer placement can
help control root spread, but it must
begin soon after the tree is planted.
Several papers by researchers Beeson
and Gilman indicated that growers were
already using this technique. Three
sample field fertilization protocols are
online at http://hort.ufl.edu/woody/
fieldfertilization.shtml.
On the other hand, one study
showed that after trees received overhead irrigation and broadcast fertilization for two years in the nursery,
concentrating the irrigation or fertilizer
close to the trunk did not influence fine
root growth.
Another researcher showed that
field-grown trees which are hardened
off survive better. During the hardening
off process, trees are dug several weeks
or months prior to shipping. Roots
begin to grow within the root ball,
and the tree makes other physiological
adjustments, including dropping some
leaves. Roots often grow through the
burlap, helping to hold together the
ball for handling, and providing more
young roots for water absorption.
The University of Florida also published information on a recent innovation that could eliminate the need for
synthetic burlap in a wire basket. Trees
are dug, placed in natural burlap and
then tied to hold the root ball tight. The
intact root ball is lowered into a predug hole lined with black nursery soil.
After regenerated roots grow partially through the fabric, it is secured
to outside of the root ball. Trees can
be held this way for many months,
depending on the species and season.
When they are lifted the sleeve on the
outside of the ball will be intact. This
holds the soil in the root ball until actual transplanting.
Surviving the digging
Whatever the method, digging a living tree creates stress, even when it is
dormant. Add the heat of summer, and
freshly dug plants can use protection.
One solution is the use of antitranspirants, which are compounds that
are applied to the leaves, forming a
short-term, protective layer that limits
water loss.
There are several compounds in
the market that have shown benefits.
One of the best known is Moisturin,
which is made by GSI Horticultural
in Bend, Ore. It was introduced a
decade ago based on research done at
Oregon State University, under Dr. Les
Fuchigami. Various Oregon growers
have used it for many years.
Jim Glessner, owner of GSI, cited
a thank you from Whitworth University
grounds department. The staff had to
move three 20-foot green ash trees in
temperatures higher than 95 degrees.
“The trees were sprayed with
Moisturin in the morning and dug in
the afternoon with a small track hoe,
loaded into the back of a large truck,”
the note stated. “Stored for 5 hot days
PLANT OREGON
The Holmac HZC 16-22 tree digger, imported by
Plant Oregon, digs field-grown trees for B&B soil.
… staked and planted … in the ground
for six weeks. The trees haven’t lost
one leaf “
Another approach is applying one
of many “transplant concentrates.”
Again, there are many choices, some
better tested than others. It is a rapidly
expanding segment — and not always
science-based.
One example is Bio-Plex, whose
marketing team came up with a simple
definition. It is a concentrated liquid
complex of many “naturally occurring”
organic compounds. These include, but
are not limited to, cold-processed seaweed extract, humic substances, numerous plant vitamins, enzymes, amino
acids, nutrient chelators, root-specific
growth stimulators, chelated iron and
micronutrients, and a new, “state of the
art” organo-silicone-based tissue and
soil penetrant.
Many of these compounds have
been shown to be beneficial, but read
the product information carefully.
So, while field crops are a slowly
diminishing segment, the modern digger equipment and other tools make
production easier to accomplish than
ever before.
Miles McCoy is the owner of Sustainable
Hort LLC, a sustainable and organic
products marketing firm. He has 25-plus
years of green industry experience
in marketing, communications and
research. He can be reached at
[email protected].
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