Pot-in-pot operations expensive to
Pot-in-pot production is
growing rapidly in the United States, most commonly among growers
of shade, fruit and flowering trees, though the system is suitable
for shrub production as well. Probably the biggest deterrent to
establishing a pot-in-pot (PnP) operation involves the expenses
of establishment. Each plant requires 2 pots, the in-ground socket
or moat pot, and the removable liner pot. In Tennessee it has been
estimated that it costs roughly $20,000 per acre to set up PnP operation
involving 10 gallon (#10s) containers (1). While nursery supply
houses (2) can furnish many different pot sizes, #15s (15 gallons)
are quite common, as well as #25s. One of the largest size PnP pots
is a #45.
Cost to establish
It's hard to generalize on the establishment costs to establish
a PnP operation. There are many variables in setting up this type
of nursery, as seen in the Table 1.
Variables in establishing a PnP container nursery:
- Pot spacing
- Pot sizes
- Years to harvest
- Drainage systems
- Slope of land
With the number of different variable involved
in setting up a PnP system, growers will have to design their own
budgets. Nursery supply houses can easily provide quotes on the
cost of supplies for materials. A drainage contractor can provide
an estimate of the costs involved for installing a buried drain
tile system, if one is needed.
The number of pots required for PnP operation will depend upon the
expected size of plant at harvest, and the in-row and between row
spacing. Common spacing in both directions has been 4'-6' for shade
trees. Remember to include alleyways between blocks in calculating
the number of pots needed per acres. Blocks refer to groups of rows.
For larger socket pots a block could be 4 rows wide. Alleyways can
be kept in sod if the site has good soil drainage. A firm base during
the wet months of the winter will be important as a surface on which
to operate machinery. Alleyways can also be surfaced with pea gravel.
The steep initial expense for all the pots can be partially off-set
by the life of the socket pots. Industry proponents of PnP report
that the socket pots can last as long as 15 years (3). Sockets pots
have typically been injection molded for durability. The liner pots
used in a PnP operation are usually blow molded, and are not as
stiff as the socket pots (1). Nonetheless they are built well and
can withstand long distance shipment. They can also be used in retail
Unless the PnP operation is established on sandy soils, supplemental
in-ground drainage will need to be considered. If there is a slight
slope to the field rain and irrigation water will collect in the
base of the socket pots. It's not uncommon to find growers having
to install PVC drain tile under every row of socket pots. Depending
upon the spacing of the rows this practice can result in having
to lay considerably more tile than would be the case for a typical
orchard or pasture. Tile lines have to be installed before any pots
are placed in the field (4).
A very nicely designed PnP nursery raising
25 gallon basswood trees for the landscaping industry
Tile lines are typically set in with laser leveling and mechanical
trenchers. Tile lines are generally installed during the dry months
of the year. After the tile lines have been installed it's important
not to avoid compacting the soil above the tile lines as this can
retard water infiltration rates (5). An agricultural engineer with
a major tile company (6) can assist with the design of a tile system.
Tile lines are typically set 2-3' deep. A properly installed drainage
system will keep the water soil water level at the depth of the
tile line, thus protecting the socket pots from flooding. Taller
socket pots will offer better total container mix aeration and thus
moisture retention. Taller pots will add to the cost of establishment
PnP operations will require supplemental water during the growing
season, though much less than traditional above ground container
stock. The plants will be growing in hard sided impervious container.
Even though some of the plants will send roots out through both
the liner and socket pot which will take up soil moisture, growers
try to reduce the so called "rooting-out" as much as they
can. It can be extremely difficult to remove these liner pots from
their sockets when the tree or shrub is ready for sale. Growers
have tried painting the inside of the liner pot with copper (7)
to reduce root escapes and circling, as well as placing fabric liners
(8) inside of the socket pots to cover the drain holes.
There is generally no irrigation runoff from a PnP farm growers
will not have to build ditches and confinement basins as would the
above ground container grower.
PnP operations typically rely on either trickle emitters or spray
stakes to water the pots. This type of irrigation requires careful
attention to water quality than would be the case with an overhead
system. Sand filtration units (9) will need to be installed in order
to keep the emitters from plugging. Workers will need to be assigned
to walking each row every day during the irrigation season to check
for clogged emitters.
On the fringe of urban areas a PnP operation can be irrigated with
the public water supply. Farm properties with valid Water Rights
are often not available. If the PNP nursery is less than 2-3 acres
city water will be affordable.
Fabric weed barriers
Given the tight spacing between the socket pots some growers revert
to using heavy duty woven polypropylene ground cloth to cover the
blocks before the socket pots are installed. In a year 2000 (1)
survey it was estimated that ground cloth could cost as much as
$1,000/acre. This is a considerably higher expense than traditional
use of residual herbicides that would be used in a field grown operation.
Given the longevity of the PnP operation growers will need to be
constantly aware of the potential for perennial weeds to establish
themselves between the pots. If the blanket of woven ground cloth
remains intact, weed growth should be greatly diminished.
Comparing different propagation methods
In a 2002 study at Auburn University (10) a comparison was made
between establishing 3 different woody ornamentals (crape myrtle,
dogwood, and Leyland cypress) using either PnP, aboveground containers,
or conventional field production. This study was based on a number
of assumptions related to starting a commercial nursery. These included
purchasing farm ground, building an office for the nursery headquarters
and a machine storage building for the implements, building greenhouses
for propagation, purchasing tractors.
Under these southern U.S. conditions, it was estimated that it
would take approximately $27,000/acre to start either a PnP or an
above ground container operation. Establishing the nursery stock
in the field directly however, only required approximately $6,500/acre.
At the end of the 3 year growing period both the PnP and the aboveground
containers operations had the highest fixed and variable costs per
acre, while the field operation was the lowest. The study then shows
that establishing a container operation, whether it involves above
or within ground production, is an expensive proposition.
The above ground container operation was considered the easiest
to start, and had the least impact on the site chosen. The PnP operation
involved the most work as the site had to be leveled and the socket
pots augured in. The PnP system was also considered the most inflexible
as there was no way to alter the spacing and layout of the socket
pots without digging them up.
If prospective growers have determined the type of woody ornamental
species they would like to propagate the PNP technique, they are
advised to set up a small test block to determine the feasibility
objectively before they commit to a larger operation.
This study shows that the producing woody ornamentals in the field
is probably the best design for producers hoping to minimize initial
capital outlay. While the field operation had the lowest establishment
cost, producers will have to own, or purchase a tree spade to dig
up stock at maturity.
pot-in-pot production system. 2003. Mark Holcomb, University
2. McConkey Company, Sumner,
3. Nursery Supplies,
Incorporated. McMinnville, OR.
an agricultural subsurface drainage system. 2001. Jerry Wright
and Gary Sands, University of Minnesota Cooperative Service.
of drained fields. 1990. Ontario Ministry of Agriculture and
Food, Adex #: 555.
Drainage Systems, Inc., Hilliard, Ohio.
and economic requirements for pot-in-pot nursery production.
2002. Robert McNiel, Department of Horticulture and Landscape Architecture,
University of Kentucky.
of 'Rotundiloba' sweetgum using Tex-R-Agroliners. 1998. John
Ruter, University of Georgia, Department of Horticulture.
stock production using the pot-in-pot technique. 2002. Hannah
Mathers, Department of Horticulture, Ohio State University.
10. The economics
of producing nursery crops using the pot-in-pot production system:
Two case studies. 2002. Charles Hall, John Haydu, and Ken Tilt,
Southern Cooperative Series Bulletin #402.
First posted: December,