CA1264554A - Root control bag - Google Patents

Abstract

Abstract of the Disclosure A process for growing nursery stock (e.g., trees, shrubs, etc.) involving the specific improvement of con-fining root propagation to a nonwoven porous polymeric fabric bag such that grown through the bag is severely constricted at the fabric, producing a girdling effect and root branching within the bag. Such a process leads to a tightly packed, highly root branched soil ball even in loose sandy loam that is easily removed from the field, readily transported and effective in re-establishing the tree upon transplanting even during the hot summer months.

Description

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ROOrr CONTROL ~AG
Back~ ound oE the Inventlon 1 Field of the Invention -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 ~6~
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

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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 6~jL~.
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 ~6~i5~

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 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

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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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~ 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 ~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.

Claims (17)

1. THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
   PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
   l. A 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 said hole a nonwoven, porous, needled, fused fabric liner formed of staple synthetic thermoplastic fibers, (c) filling said liner with growing media; and (d) planting and growing a plant within said liner in the earth such that the liner and the growing plant can later be removed from the earth as a single unit for transporting and transplanting.
2. 2. A method of claim 2 wherein said liner is a non-woven polyolefin fabric.
3. 3. A method of claim 2 wherein said fabric liner is formed of fibers selected from the group consisting of polyolefin fibers, polyester fibers and polyamide fibers.
4. 4. A method of claim 2 wherein said fabric liner is formed of staple polypropylene fibers and said fabric is at least partially fused by infrared radiation.
5. 5. In a process for growing nursery stock having an increased tolerance to hot weather transplanting, the speci-fic improvement comprising:
   (a) excavating a hole in the earth;
   (b) inserting within said hole a nonwoven, porous, needled, fused fabric liner formed of staple synthetic thermoplastic fibers;
   (c) filling said liner with growing media; and (d) growing a plant within said liner in the earth such that the liner and the growing plant can be transported as a single unit.
6. 6. A process of claim 5 wherein said plant is a con-tainer grown nursery stock plant.
7. 7. A process of claim 5 wherein said fabric liner is formed of fibers selected from the group consisting of polyolefin fibers, polyester fibers and polyamide fibers.
8. 8. A process of claim 5 wherein said fabric liner is formed of staple polypropylene fibers and said fabric is at least partially fused by infrared radiation.
9. 9. In a method for the growing of nursery stock plants intended for transplanting wherein the roots of the plants are confined to containers filled with growing media, the specific improvement comprising making said container from a nonwoven, porous, needled, heat fused fabric formed of staple synthetic thermoplastic fibers wherein said fabric is operatively capable of pruning said roots and inducing root branching when said roots penetrate said fabric.
10. 10. A method of claim 9 wherein said fibers forming said fabric are polypropylene fibers.
11. 11. A root pruning nursery stock container with plant comprising a nonwoven, porous, fiber bonded fabric bag formed of staple synthetic fibers operatively capable of pruning plant roots and inducing root branching when said roots penetrate said fabric bag a plant and growing media.
12. 12. A root pruning nursery stock container of claim 11 wherein said fabric bag is formed of staple polypropylene fibers.
13. 13. A method of girdling the root growth of a plant comprising the step of introducing a nonwoven, porous, fiber bonded fabric barrier formed of staple synthetic fibers in the path of said root growth such that said root growth penetrates said fabric and is girdled as it attempts to develop.
14. 14. A method of claim 13 wherein said fabric is formed of staple polypropylene fibers.
15. 15. A method of controlling the root growth of nursery stock prior to transplanting such nursery stock comprising the steps of:
    confining said root growth within a root control barrier formed of a nonwoven, porous, bonded staple polymeric fiber fabric having suf-ficient porosity and structural strength to allow initial penetration by roots but to constrict such roots whereby root growth out-side said barrier is restricted and enlarged root nodule formation and root branching are promoted within said barrier; and removing said root growth from said barrier prior to transplanting said nursery stock.
16. 16. The method of claim 15 wherein said nonwoven, porous, staple polymeric fiber fabric is at least partially bonded by infrared radiation fusion.
17. 17. The method of claim 16 wherein said nonwoven, porous polymeric fabric is formed of staple polypropylene fibers.