Note: Descriptions are shown in the official language in which they were submitted.
f.~
ROOrr CONTROL ~AG
Back~ ound oE the Inventlon
1 Field of the Invention
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This invention relates to a method of controlling plant
root growth. More specifically, the invention relates to a
method of growing plants in the field wherein the root
9rowth is controlled by the presence of a porous plastic
bag.
2. Description of the Prior Art_
The basic concept of growing nursery stock, such as
trees and the like, in containers is a well known commercial
activity. However, the growing of trees in a container is
efficient and economical only during the early period of the
plant's development and is pragmatically restricted to con-
tainers no larger than about five gallons in size. Goodale,Toby W. and Whitcomb, Carl E. in a pair of articles entitled
"Producing Woody Ornamental Shrubs in Containers, Costs of
Production and Projected Profits", Ornamentals South, Vol 2
(4~; pages 20 through 25 (1980) and "Producing ~oody
Ornamental Shrubs in Containers, Influence of Fertility
I,evel and Container Size", Ibid. ~oL 2 (3); pages 10 through
13 (1980~, found that for most plants there is an optimum
container size ~or growth of the particular plant with maxi-
mum economic return. Generally, it was found that to grow
trees in containers more than two years was not economically
feasible.
Contemporary improvements in the fundamental understand-
ing of the nutrition of tree seedlings (and plants in gener-
al; for example, see U. S. Patent 4,328,025) both in the
propagation container and subsequent larger container have
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led to improved growth rates. Furthermore, recent develop-
ments in various aspects of air-root pruning of the tree
seedling to destro~ the tap root and stimulate a much more
fibrous root system (such as described in U.S. Patent No.
4,574,522 (Whi-tcomb) issued February 5, 1985) further
complicates the commercia]. economics of growing trees in
containers in that the tree outgrows the container before
the comrnercial distribution and sales take place. Thus, the
also well known basic concept of growing plants such as
trees and the like in containers until the youn~ plants are
mature enough to be transplanted to a field in a relatively
compact or dense planting arrangement wherein their
development continues until sold appears to be pragmatically
a necessary commercial practice. This conclusion is further
supported when considering the additional problems
associated with the alternative of continuing the tree
growth in a container. Namely, high summer temperatues
reduce top and root growth principally due to the abnormally
high soil temperatures in the container, while low winter
temperatures may damage or kill roots even though the tops
would have normally survived the winter if planted in the
field and the vertical growth of trees fre~uently results in
containers being blown over which means they must be
straightened before watering and the like.
In contrast to the above problems~ an article by
Hogan, Charles and Whitcomb entitled "Producing Container
Nursery Stoc~ in the Field" Research Report P-705 of the
oklahoma Agricultural Experimental Station, Pages 43-44
~1974) observed that if plants could be produced in
containers buried in the field, the surrounding soil would
insulate the
I
5~i~
container frorn high summer temperatures and low winter tem-
peratures~ while holding plants upright at all times without
stakiny. However, in order for such a system to ~unction, a
procedure must be developed to confine the roots to the
growing medium in the container. Otherwise, the roots would
grow out of the container into a large mass oE soil~ thus
~equiring digging and cutting before marketing. One of the
major advantages to container grown stock is that most of
the roots go with the top of the plant at marketing, thus no
shock or adjustment occurs. It was felt that nearly one
hundred percent retention of roots must be maintained if the
field production with con-tainer system is to be considered.
Summary of the Inventlon
In view of the prior art, we have discovered an in-the-
field method of controlling the root growth of nursery stock
intended for transplanting comprising the steps of:
(a) excavating a hole in the earth;
(b) inserting within the hole a nonwoven porous
polymeric fabric;
(c) iling the fabric with growing media; and
(d) planting and growing a plant within the abric
in the earth such that the fabric (i.e., root enclosure bag)
and the growing plant can later be removed from the earth as
a single unit for transporting and transplanting.
Thus, according to one embodiment of the present inven-
tion, a nursery stock plant is placed (transplanted in -the
field) into a growing media conined by a nonwoven porous
polymeric fabric bag. Preferably, the nonwoven porous poly-
meric fabric is a nonwoven, bonded polymeric fiber fabric30
~;~6~LSS~
formed o~ staple polyrneric thermoplastic ~ibers such as the
products produced and sold by Phillips Fibers Corporation, a
subsidiary of the Phillips Petroleum Company under the trade
nam~s Petromat and Supac Filter Fabric.
For further explanation o the nature of the nonwoven,
porous, polymeric fabric marketed by Phillips Fibers
Corporation employed in the containers acco-rding to the pre-
sent invention, see U. S. Patents 4,042,644; 4,15~,889 and
4,199,G44 assigned to Phillips Petroleum Company wherein
methods and equipment for the production of needle bonded,
drafted, fused, batts or webs of nonwoven synthetic fabric
from polymers such as polyolevin, polyester and polyamide
are disclosed. Typically, the fabric is manufactured ~rom
synthetic staple fibers preferably made into batts with
fibers oriented in the fill direction. The batt is then
subjected to drafting (stretching) in the warp and/or fill
directions wi-th needling (needle bonding) and fiber fusion
~infra-red radiation, heated roller or hot fluid). Fabrics
characterized by various batt weights from 1 to about 20
ounces per square yard using preferably staple lengths of
about one and a half to ten inches of from abou-t one to
twenty denier, at needled densities of from about one
hundred to one thousand punches per square inch and draft
ratios of about 1.01 to 4 are described, all of which, for
purposes of this invention and claims herein, are collec-
tively referred to as "nonwoven, porous, polymeric fabric".
In other words, the present invention provides in a
method for the growing of nursery stock intended for trans-
planting whe-rein the roots of the plant are confined to a
container partially filled with growing media, the specific
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improvement comprising; making the container from a nonwoven
porous polymeric fabrlc wherein the fabric is operatively
capahle of pruning said roots and inducing root branching
when said roots penetrate said fabric.
It is an object of the present invention to provide a
barrier or container to be used either below or above grade
that partially confines plant root propagation, restricts
lateral root extension, controls root swirl and partially
root prunes at the surace of the container; thus stimu-
lating and accelerating root branching within the container.10
It is an ancillary object that this barrier be a fabric that
can be made into a bag or other root restrictive liner such
that the container confines more of the roots to the inter-
ior of the bag and simultaneously functions in a manner ana-
logous to the traditional ball and burlap technique of15
transplanting trees or the like. The fulfillment of these
objects and the presence and fulfillment of additional
objects will be apparent upon complete reading of the speci-
fication and claims taken in conjunction with the attached
drawings.
Brief Description of the Drawings
FIGURE 1 illustrates a root ball of a tree grown in a
root control bag according to the presen-t invention.
FIGURE 2 illustrates the root structure of a plant after
growth in -the root control bag according to the present
invention.
FIGURE 3 illustrates the circumferential constricted
root growth that occurred as the root penetrates the fabric
bag and as was severed by removal of the fabric along with
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the resulting root branching induced by the ~oot cont~ol bag
according to the present invention.
~escription of the Preferred Embodiments
The method according to the present inventiont in the
broadest sense, involves the use of a porous plastic bag,
whether above grade or below, to confine plant root propaga-
tion to essentially the interior of the bag. Preferably,
the bag is made from a synthetic, decay resistance nonwoven,
porous polymeric fabric having sufficient structural
strength that it will serve as the equivalent to the burlap
wrapping during subsequent transplanting of the plant to its
final location. Thus, the method according to the present
invention is envisioned as being effective during inter-
mediate stages of the development, handling, shipping andstorage of the plant.
Preferably, the bag or more specifically, the fabric
employed to make the bag, should have sufficient structural
integrity and/or be suf~iciently impervious to root penetra-
tion such that the root growth will only partially penetrate20
the fabric. Because of the partial penetration of the bag,
the root growth at the surface of the fabric will be severe-
ly constricted, thus promoting root branching as well as
accumulation of carbohydrates within teh bag which in turn
supports rapid root growth following removal of the bag.
One particular type of fabric meeting the foregoing require-
ments is a nonwoven porous polymeric staple fiber fabric
manufactured by Phillips Fibers Corporation and sold under
trade names Petromat or Supac Filter Fabric. However, other
nonwoven, porous, bonded polymeric fabrics, plastics and
other liner matericlls are envisioned as being equivalent Eor
purposes of this invention, provided the requisite porosity
and structural strength as well as resistance to deg-radation
when buried in the earth and ultra-violet stability when
used above grade are achieved. Thus, many of the vinyl com-
positions or vinyl coated fabrics are to be considered
e~uivalent for purposes of this invention.
As mentioned above, the preferred fabric fo-r use in
accordance with the present invention is a nonwoven, porous,
polymeric fabric of the type described in U. S. Patents
~,1S4,889; 4,042,655; and 4,199,644. Paten-t 4,154,889
issued May 15, 1979, describes -the basic method of forming a
non-woven, needled fabric from staple synthetic thermoplas-
tic Eibers selected Erom the group of polyolefin, e.g.,
polypropylene, polyes-ter and polyamide fibers. The method
involves, among other things, Eorming a needled bat of the
fibers and optionally heat fusing the fibers in the bat
using heated rolls. Patent 4,042,655 issued August 16,
1977, describes improvements in the forming method and
fabric including, among other things, fusing at le~st a por-
tion of the fibers by infrared radiation. Patent 4,199,6~
issued April 22, 1980, describes additional improvements in
the forming method and fabric, particularly in needling the
fabric. The most preferred fabric for use in acco-rdance
with this invention is a nonwoven, porous, bonded polymeric
fiber fabric of the type marketed under the trade names
Petromat and Supac Filter Fabric ~y Phillips Fibers
Corporation. Such fabrics are formed in accordance with the
teachings of one or more of the above-mentioned patents, and
specifically are nonwoven, porous, needled, fused fabrics
formed of staple synthetic thermoplastic fibers.
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One particula~ attribute o~ such nonwoven porous, bonded
staple polymeric fiber fabric that makes it particularly
useful in the present invention is the observed tendency or
roots to go through the fabric, but further development of
the root is restrictecl. This cessation of eoot growth is
caused by severe restriction, or more specifically, circum-
ferential constriction applied by the Eab-ric to the root as
a result of the staple fibers in the fabric being bonded
together by needling (sewing together) and/or by fusion.
Consequently~ the root after penetrating the fabric is unable
to increase in diameter within the fabric leading to a
girdling effect at the bag. Literally, a nodule or enlarge-
ment of the root will occur on either side of the Eabric
barrier with a fine root thread through the fabric connecting
the two sides. This restriction at the fab-ric severely
retards root growth outside the bag and so represents a
naturally weak structural point for root breakage when
removing the bag during subsequent transplanting. However,
a more important feature of this type of root growth, or
perhaps, more accurately the lack of root growth ~i.e., phy-
sical root pruning) is the tendency for it to induce root
branching on the inside of the bag in a manner analogous to
what occurs when air-root pruning, or, in fact, other plant
pruning takes place. Because of the root pruning effect of
the fabric bag and the associated secondary branching behind
the root tip, a very fibrous compact root system will deve-
lop within the confines of the bag. ~urthermore, the re
striction at the fabric promotes the root storage of carbo-
hydrates within the bag. These features of the present
invention are felt to be novel and extremely useful, leading
3L~6~5~
to a ~series oE unexpected results and advantages (e.g., the
observation of twenty inches of additional root growth
within seven weeks of transplanting a river birch and a
count of over 5,000 root branches on a green ash, as exem-
plified later).
Since the root branching is induced within the confines
of the bag and the plant with the bag is -removed as a single
unit for purposes of transplanting, the number of root ends
available as well as the relative percentage of the total
root structure available for re-establishing the plant after
transplanting is maximized. Consequently, the odds of sur-
vival after transplanting even under adverse conditions is
enhanced. Also, the -resistance to or the ability to survive
transplantation during hot summer months is also enhanced.
For all practical purposes, trees grown according to the
method of the p-resent invention can be transplanted success-
fully throughout the hot summer months, even in the southern
states (as exemplified later). Thus, the method according
to the present invention extends the season for transplant-
ing well beyond that which is ordinarily employed in the20
industry.
The very fibrous root ball structure within the bag also
allow the usa of sandy loam soils or other relatively loose
growing media which were not particularly compatible with
the prior art ball and burlap technique. ~lso, the inherent
girdling e~fect along with cessation of external root propa-
gation tends to allow for easy removal o~ the plant, root
ball and fabric bag as a single unit, making the overa]l
transplanting operation extremely easy and highly success-
ful. Thus, the present invention preserves essentially all30
s~
of the advanta~es associated with planting in the field
(i.e., root protection ~rom temperature extremes and preven-
tion of trees and the like from being blown over), yet sup-
plements these advantages with several highly desirable
additional features.
The use of the nonwoven porous polymeric fabric bag
liner according to the present invention is straight~orward.
If the plant is to be grown below grade, an appropriate hole
is excavated or dug in the field and the bag is inserted as
a liner, otherwise, the bag can be placed at an appropraite
location above grade. Optionally, a plastic ~ilm barrier
can be placed in the bottom of the hole (or on the ground
for above grade use) before inserting the bag liner. Any
appropriate growing media can -then be placed within the
bag. The plant is then placed in the growing media and
allowed to grow. In principle, the plan-t can be at essen-
tially any early stage of development, including planting
the seed or seedling directly in the field. For all prac-
tical purposes, it is envisioned that the pre~e~red commer-
cial utilization of the invention will involve the trans-
planting oE one o~ ~ive gallon container grown nursery stock
into tne buried liner bag (or tightly packed above grade
bags) when the plants can no longer be optimally sustained
in the container. Because of the possibility of close
spacing and the presence of the fabric bag with associated
root growth confinement, proper water management during this
stage of plant development is critical.
The bag liner itself can be manu~actured in essentially
any appropriate size or shapeO Preferably, it will be sewn
or glued along seams producing a root confining structure
--10--
S59L
that wilL serve as the soil reLeasing unit during final
~ransplanting o~ the plant. This bag is physically ~emoved
from the root ball as the last step befo~e replanting.
The following example is presented to illustrate one pre-
ferred embodi~ent of tlle overall process according to thepresent invention.
EX~MPLE
Using a ~-ounce Supac Filter Fabric manufactured by
Phillips Fibers Corporation, a subsidiary of Phillips
Petroleum Company, a series of bags were sewn together.
Each bag was approximately 20 to 24 inches in diameter and
about 12 to 14 inches deep. Holes 24 inches in diameter
were prepared by an auger in a sandy loam soil. A single
disc of 6 mil polyethylene film of 24-inch diameter was
placed at the bottom of each hole. The bags were then
placed in the hole and filled with loose soil removed by the
auger. Loblolly pine, river birch and green ash tree
seedling that had been air-root pruned in bottomless con-
tainers for about three months and then grown in two-gallon
poly bags for the remainder of the growing season were
transplanted in December into the bags.
~ he soil of the entire field had been fertilized pre-
viously to provide about 75 pounds per acre of P2O5 and 300
pounds per acre of K2O. Nitrogen was broadcast over the
entire field at about 200 pounds per acre using urea.
During the following months, the trees were drip irri-
gated to stimulate growth and prevent moisture stress. Weed
control was accomplished with Ronstar pre-mergent herbicide
at about 2 pounds active ingredient per acre along with spot
spraying with Roundup contact herbicide as needed.
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After twenty-one months in the Eield, loblolly pine has
reached 8 feet tall with 2V2-inch stem calliper and river
birch were 10 feet tall with 2~-inch calliper. In late
August of the third growing season, three trees of each spe-
cies were dug by inserting a sharp square pointed -Elat blade
shovel around the fabric bag to the depth of the polyethy-
lene sheet and the trees were lifted from the soil by hand.
The trees with bagged root balls intact were transported
approximately 38 miles and then replanted into a sandy loam
soil after removal of the bag. The temperature was in
excess of 100F on the days the trees were dug and
replanted, yet no wilting or subsequent leaf drop occurred.
All trees survived.
The effect oE fabric bag on roo-t development was
apparent upon examining the roots of the trees. As the
roots of the tree 10 grew outward and downward (see Figure
2), they penetrated the fabric bag 12 generally whenever
contact with the fabric was made. However, as sequentially
illustrated in Figure 2, the nature of the penetration was
highly restrlcted in that the roots 14 that penet-rated the
bag 16 grew in diameter on the inside of the bag, dimi-
nished to a very small diameter as they passed through the
fabric, enlarged somewhat 18 on the outside of the bag 16
and then quickly dec~eased in diameter; thus, the fabric
constricted the roots causing a severe girdling effect.
Thus, the tree still in the root control bag typically exhi-
bited only relatively small diameter roots external to the
bag. As illustrated in Figure 3, the root 20 tended to
break at the girdling 22 caused by the physical pruning at
the fabric. Because of this root pruning, secondary
3~
branching 24 would take place behind the tip.
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For example, the roots of the green ash tree tended to
break at the girdle corresponding to passing through the
bag, thus exposing a highly branched, fibrous root structure
which had developed within the bag~ This is considered
novel and unexpected in that the green ash tree is known to
be difficult to transplant because of the lack of a fibrous
root structure. In attempting to quantitatively define and
measure the fibrous root structure observed in the green ash
tree, a selected surface count of root branches extrapolated
to ~he size of the root ball resulted in an estimated 5,037
total roots being present. Prior to the present invention,
150 roots would be an extraordinary value for a green ash.
The typical root of the loblolly pine as it approached
the fabric bag from the inside of the bag was about one-half
inch diameter, but reduced to less than one-eighth inch
diameter on the outside oE the bag and tended to sever at
the girdle when the bag was removed, thus exposing a blunt
root nodule. This restriction in lateral root development
also stimulated secondary branching behind the root tip
nodule within the bag similar to the branching accomplished
by air-root pruning. The enlarged root nodule 26 (see
Figure 2) is felt to represent a natural carbohydrate reser-
voir or storage (i.e., phloem carbohydrates 2~ from leaves
and H2O/nutrient xylem 30) which enhances subsequent root
growth and re-establishment of the plant after transplant-
ing. The increased branching tends to hold the soil ball
together in a very solid mass as opposed to the normal ball
and burlap method, thus also improving the transplant-
ability. Likewise, following removal of the bag and re-
planting, many more root tips exist to grow into the sur-
rounding soil and anchor and establish the tree.
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~26~55~
~ he rapid re-establishrnent of the roots of a river birch
tree grown in a root control bag and transplanted aEter
removal of the bag was confirmed by observations of a
twenty-inch se~ment of new root growth approximately the
thickness of a pencil after transplanting. This root growth
took place in seven weeks and roots were found as far as
three feet f~om the outer perimeter of the root ball.
Although the method according to the present invention
involves the expenditure of additional capital and labor at
a relatively early stage of the growth of the tree, the
overall advantages of the system are felt to more than com-
pensate for the costs involved. First and foremost, the
present invention extends the digging and transplanting
season well beyond that of the previously known conventional
ball and burlap technique. This is accomplished in part
because the balls can be smalle-r and lighter while still
containing (because oE branching~ a higher p-roportion of
roots than the conventional ball and burlap. Success in
transplanting is also due in part to availability of accu-
mulated hyrocarbons which nourish subse~uent root growth.
Because of the compactness of the root ball, sandy loams
unsuitable for the ball and burlap technique can now be used
in the present system, while a much higher proportion of the
roots are retained in the ball. Consequen-tly, the trees of
the present invention can be held easier and longer on
retail lots without rewrapping with burlap. Andt less time
and effort is required in digging and transplanting the tree
grown in the fabric bag of the present invention. In fact,
trees grown in the root control bags according to the pre-
sent invention have been successfully transplanted without
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~2~;~5~i~
digcJin-J by me~l-ely Lifting the tree, root ball and bag
directly out of the ground In using the root control bag
above grade, many of the advantages of thermal insulation
and protection from the wind can be achieved by close
packing of the root bags with plants while all o~ the other
inherent advantages of the root control bag are preserved.
Having thus described and exemplified the invention with
a certain degree of particularity, it is manifest that many
changes can be made in the details of the construction of
the fabric bag and the method of employing he bag without
departing from the spirit and scope of this invention.
Thereore, it is to be understood that the inventlon is not
limited to the speciEic embodiments set forth herein for
purposes of exemplification, but is to be limited only by
the scope of the attached claims, including a full range of
equivalents to which each element thereof is entitled.
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