Abstract:
An apparatus bounds and retains the medium in which a transplantable plant is grown, and promotes the production of lateral root tips by such a plant at all levels in the growth medium. The apparatus includes a sheet having a plurality of hollow protuberances formed with proximal protuberance openings that communicate with distal protuberance openings. The protuberances provide pathways that mimic the natural tendency of the plant roots, so as to decrease the likelihood of the root tips evading the protuberances and promote root-tip growth towards the distal protuberance openings whereby air-root pruning is assured.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates generally to a container for growing plants, and, more particularly, to a container for growing plants such as trees and shrubs for transplanting.  
           [0003]    2. Description of the Prior Art  
           [0004]    Plants, such as trees and shrubs, which are intended to be transplanted are commonly grown above ground in containers. Such containerized plants can be grown at a faster rate than those grown in the ground, they are more easily tended, and because the roots of the plants are not severed when the plants are transplanted, transplanting is more often successfully accomplished.  
           [0005]    Various types of containers have been used for growing plants, by retaining and bounding the soil and roots of plants prior to transplanting. For example, metal cans and cylindrical plastic containers with holes in the bottoms were among the first plant growing containers used.  
           [0006]    When a plant seed germinates the first or primary root, often referred to as a taproot, plunges downward in an effort to secure the new plant in place and to secure access to moisture and nutrients. The taproot on some plant species extends only a few inches while in others the taproot extends 10 feet or more if environmental conditions in the soil allow.  
           [0007]    A smooth-walled conventional container for growing transplantable plants is illustrated in FIG. 1 and generally designated by the numeral  1 . The container  1  is comprised of a cylindrical body having a continuous arcuate sidewall  3  for bounding and retaining a transplantable plant  5  having taproot  7  in a volume of soil or other growth medium  9 . The taproot  7  grows until it reaches the bottom of the container, and then changes direction in response to impacting the container while continuing to grow until circling becomes physically restricting to growth.  
           [0008]    Once the taproot stops growing or extending, the apical dominance of its root tip is lost and the development of some secondary lateral rooting occurs. The secondary roots are much less influenced by gravity and extend more horizontally, although still partially downwardly, in direction. When such roots contact the sides of a plant container, unless trapped or air-pruned they turn and grow downwardly in a spiral path along the sides to the bottom of the container where they continue to grow in a circular pattern. As further roots form off the secondary roots, called tertiary roots, these roots have an even greater horizontal tendency, but still retain a modest downward tendency and often end up in circular patterns at the bottom of a smooth inner-walled, conventional container as well.  
           [0009]    Plants that are transplanted with root growth that extends downwardly and concentrated at the bottom of a container, as described above, suffer because the roots provide little or no lateral anchorage of the plant, and the tips of the roots are at a depth in the soil where aeration is less favorable. In addition, the downwardly-directed roots are intermingled with each other and as they increase in diameter with age, they exert pressure on one another that can restrict the normal flow of water and nutrients through the roots.  
           [0010]    Cylindrical containers having holes in the sides to inhibit such concentrated spiral and circular root growth have been utilized in the art. The side holes or openings function to cause air-pruning of the roots, a phenomenon in which the growth of a root stops when the root extends into the vicinity of an opening that is exposed to the atmosphere, essentially because the atmosphere cannot provide the requisite moisture necessary for continued growth. While the use of cylindrical containers with side holes reduces the incidence of spiraled and circled roots, some spiraling and circling can still take place because the roots are not positively directed towards the side holes and can evade the side holes by ricocheting off the inner surfaces of the container sides between the holes.  
           [0011]    Transplantable landscape plants have also been grown in square, bottomless containers placed on wire screens whereby roots reaching the bottom of the container are air-pruned. Most of the resulting root tips end up at the bottom of such containers, reducing lateral anchorage. Furthermore, the requirement of placing the containers on wire screen surfaces generally makes the practice cumbersome and uneconomical.  
           [0012]    Other containers have been developed (see, e.g., U.S. Pat. No. 5,099,607 issued on Mar. 31, 1992) that employ a plurality of complementary outwardly and inwardly projecting regions. A section of such a container is shown in FIGS. 2A-2B. The inwardly projecting regions  13  terminate in closed tips  15  and the outwardly projecting regions  17  each have an opening  19  at its tip such that when roots are guided to the openings, the tips of the roots are dehydrated by exposure to air and effectively air-root pruned, thereby stimulating root branching. These container designs work fairly well, but also exhibit some shortcomings. In particular, it has been observed that numerous roots of a plant disposed in such containers will evade the air-root-pruning openings, in part, because in use the outwardly projecting regions  17  have lower inner surfaces  21  that slope upwardly (i.e., upwardly and outwardly) and are therefore substantially normal to the naturally-occurring paths—outwardly and downwardly—that a large majority of the roots will follow. The root tips encountering such upwardly-sloping surfaces  21  tend to be deflected or ricocheted away from the pruning openings  19 .  
           [0013]    It is therefore highly desirable that each root of a transplantable plant that would otherwise extend outwardly and contact the sidewall of a plant container be guided to an opening for air-root-pruning and not be allowed to ricochet off the container sidewall and extend down the sidewall or horizontally around the container.  
           [0014]    It is further desirable to provide an improved container for growing transplantable plants, whereby spiral and circular root growth is reduced or prevented, and the development of lateral root tips (axially) along and (circumferentially) around the sides of the container is maximized.  
           [0015]    It is still further desirable to provide a sheet that is formable into an improved plant growth container wherein the production of lateral root tips is promoted at all levels in a plant growth medium and the root tips quickly grow in all natural directions, whereby the plant is quickly laterally anchored when transplanted and maximum water and nutrients are absorbed.  
         SUMMARY OF THE INVENTION  
         [0016]    One embodiment of the present invention provides an apparatus for bounding a medium in which a transplantable plant is grown, i.e., an apparatus for containing a transplantable plant. The term “transplantable” is generally used herein to refer to a plant that is able to be transplanted easily, but does not dictate that the plant ever actually be transplanted. The apparatus promotes air-root pruning and includes a sheet having a plurality of hollow protuberances. The term “sheet” is used herein in a conventional sense, i.e., to mean something that is thin in comparison to its length and breadth, but not necessarily having a uniform cross-section or thickness. Nor is the term “sheet” intended to preclude thin materials that have indefinite lengths and are rolled in a cylindrical shape for convenient storage and dispensing. It is indeed preferable that a sheet according to the present invention is formed of a thin, flexible plastic material having an elongated length to facilitate rolling in cylindrical fashion, whereby a plurality of sheets having shorter lengths may be cut from the roll as needed to contain transplantable plants. The term “protuberance” is also used herein in a generally conventional sense to mean something that thrusts outwardly from a surrounding or adjacent surface.  
           [0017]    The sheet protuberances are formed with a proximal opening that communicates with a distal opening. Each protuberance generally slopes downwardly and outwardly when the sheet is positioned upright. Preferably, the center of the proximal opening is positioned higher than the center of the distal opening when the sheet is positioned upright, ensuring that the pathway provided by the protuberances mimics the natural distribution tendency of plant roots.  
           [0018]    It is also preferable that the proximal opening of each protuberance is larger than the distal opening thereof, so as to assist in directing root extension towards the distal opening.  
           [0019]    It is also preferable that each of the protuberances narrows in width or cross-section from the proximal opening to the distal opening, again for assisting in directing roots towards the distal opening, in funnel-like fashion. This narrowing may be in a substantially linear fashion, such as in conically-shaped or pyramidally-shaped protuberances. This narrowing may also be substantially curvilinear, such as in a hemispherically-shaped protuberances.  
           [0020]    The openings of the protuberances may also employ different shapes. For example, the proximal opening may be substantially rectangular, substantially circular, or irregular in shape. Similarly, the distal opening may be substantially rectangular, substantially circular, or irregular in shape.  
           [0021]    The protuberances may also employ different profiles. The term “profile” is used herein generally to mean the defining or outlining wall portions of a protuberance when viewed in cross-section or from the side. For example, “lower profile” means the wall portion of a protuberance that defines its lower outline as seen from the side. In various embodiments, the protuberances may have a lower profile that is substantially horizontal, a lower profile that slopes slightly upwardly at an angle that exceeds 90 degrees measured from the plane of the sheet, or some combination thereof. Furthermore, in some embodiments, the protuberances may have an upper profile that slopes downwardly at an angle in the range of approximately 110 to 150 degrees measured from the plane of the sheet, or some combination thereof.  
           [0022]    As mentioned above, it is preferred that the sheet is sufficiently flexible to be formed in a generally cylindrical shape. It is further preferred that the sheet be either: (a) provided with a fastener(s) to secure the edges of the sheet together when it&#39;s formed in the generally cylindrical shape; or (b) seamlessly formed in a generally cylindrical shape, such as by injection molding. The fasteners may be integral with the sheet or provided as a separate component coupled to the sheet.  
           [0023]    The plurality of protuberances on the sheet preferably forms a lattice over at least a substantial portion of the sheet. It is further preferred that the protuberances are arranged in a close-packed configuration, for example, a configuration that employs little or no spacing between adjacent protuberances, which reduces the presence of areas in the sheet that might promote root deflection or ricocheting away from the protuberances.  
           [0024]    In one embodiment, the sheet is formed in a generally cylindrical shape by joining the edges of the sheet together. For example, this may be achieved by overlapping one of the edges over the other of the edges, and securing the one edge over the other edge along the length of the edges by using rivets, self locking rivets, or other conventional fasteners. Preferably, the overlapping of the edges is guided by the engagement of a lattice of root-directing protuberances in the region adjacent the one edge with a complementary lattice of root-directing protuberances in the region adjacent the other edge. In a further alternative, the edges of the sheet are joined together by joints formed in the edges, such as mortise and tenon joints, snaps, and hooks.  
           [0025]    It is further preferred that the sheet is naturally planar, and generally defines a plane in which a portion of each of the protuberances lies. Thus, in one embodiment, the sheet defines a plane in which the proximal opening of each of the protuberances lies.  
           [0026]    In a further embodiment, the sheet has an inner face and an outer face, and all the protuberances thrust outwardly in the direction of the outer face. The inner face includes the innersides of the planar portion of the sheet in this embodiment, as well as the innersides of the plurality of protuberances. The outer face includes the outersides of the planar portion of the sheet—if any—and the outersides of the plurality of protuberances. This may be contrasted with other embodiments wherein the plurality of protuberances are staggered such that adjacent protuberances thrust in opposite directions, i.e., some in the direction of the inner face and some in the direction of the outer face, but only the latter (outer-facing) set of protuberances have the distal openings for air pruning. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0027]    So that the above recited features and advantages of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof that are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.  
         [0028]    [0028]FIG. 1 is an elevational view, partially in cross-section, of a container for growing a transplantable plant as is generally known in the prior art.  
         [0029]    [0029]FIG. 2A is a perspective view of a portion of a particular prior art container for growing a transplantable plant.  
         [0030]    [0030]FIG. 2B is a cross-sectional view of the prior art container section shown in FIG. 2A.  
         [0031]    [0031]FIGS. 3A and 3B are front and side views of a sheet adapted for forming a plant container in accordance with one embodiment of the present invention.  
         [0032]    [0032]FIGS. 4A and 4B are front and side views of a sheet adapted for forming a plant container in accordance with another embodiment of the present invention.  
         [0033]    [0033]FIGS. 5A and 5B are front and side views of a sheet adapted for forming a plant container in accordance with a further embodiment of the present invention.  
         [0034]    [0034]FIG. 6 is a side view of two sheets oriented for stacking, or overlapping, in accordance with the embodiment shown in FIGS. 3A and 3B.  
         [0035]    [0035]FIG. 7A is a perspective view, partially cut-out, illustrating the overlapping of the edges of a sheet adapted for forming a plant container in accordance with a still further embodiment of the present invention.  
         [0036]    [0036]FIG. 7B is a side view of one of the edges of the sheet shown in FIG. 7A.  
         [0037]    [0037]FIG. 8 is a perspective view of a container bounding a volume of soil and a transplantable plant in accordance with the embodiment shown in FIGS. 7A and 7B. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0038]    The roots of a plant grow and extend in somewhat analogous fashion to the path of a projectile such as a bullet. Thus, a root will extend in a naturally promoted direction (i.e., downwardly and outwardly) until it strikes something that it cannot move or penetrate. At that point, the root is deflected or ricochets in a new direction and extends until it encounters something else that would change its direction of growth or travel. The present invention utilizes boundary-forming sheets having multiple protuberances that mimic the natural root path so as to minimize ricocheting or direction changes that lead the root away from openings that serve to air prune the root. Thus, the protuberances employed by sheets according to the present invention receive many roots without any ricocheting, and also directs root ricocheting—if any occurs —towards the air-pruning openings.  
         [0039]    In this manner, the protuberances are well adapted for engaging or intercepting the roots of a plant such as a container-grown plant at the earliest opportunity, while such roots are extending in a generally outwardly and downwardly direction, and directing such roots towards distal openings that serve to air-prune the root tips and stimulate further root branching. This may be contrasted with prior art plant containers, such as smooth-walled containers of the type shown in FIG. 1, that inhibit the growth of lateral root tips at all levels in a plant growth medium because the roots that contact the container sidewall are deflected and circle aimlessly.  
         [0040]    Referring now to FIGS. 3-5, the present invention employs a sheet  10   a - c  having a plurality of protuberances  12   a - c , respectively, formed thereon over substantially the entire surface of the sheet. Each protuberance  12   a - c  is defined by a proximal opening  14   a - c  that communicates with a distal opening  16   a - c , respectively, as illustrated in the side views of FIGS. 3B, 4B and  5 B. Each protuberance generally slopes downwardly when the sheet is positioned upright. Preferably, the center  22   a - c  of the proximal opening  14   a - c  is positioned higher than the center  24   a - c  of the distal opening  16   a - c  when the sheet is positioned upright, ensuring that the pathway provided by the protuberances mimics that natural downward and outward growth tendency of the plant roots.  
         [0041]    Preferably, the proximal opening  14  of each protuberance  12  has a larger cross-sectional area than the distal opening  16  thereof, and each of the protuberances narrows in width from the proximal opening to the distal opening, so as to assist in directing root extension towards the distal opening, in funnel-like fashion. This narrowing may be in a substantially linear fashion, such as in conically-shaped (see FIGS. 4-5) or pyramidally-shaped protuberances (see FIGS. 3A-3B). This narrowing may also be substantially curvilinear, such as in a hemispherically-shaped protuberances (not shown).  
         [0042]    The openings of the protuberances may also employ different shapes. For example, the proximal opening may be substantially rectangular, substantially circular, or irregular in shape. Similarly, the distal opening may be substantially rectangular, substantially circular, or irregular in shape. Thus, the sheet embodiment shown in FIGS. 3A-3B employs square-shaped proximal and distal openings; the sheet embodiment shown in FIGS. 4A-4B employs circular proximal and distal openings; and the sheet embodiment shown in FIGS. 5A-5B employs square proximal openings with round distal openings.  
         [0043]    The protuberances  12  may also employ different profiles. For example, the protuberances may have a lower profile  28   c  that is substantially horizontal (see FIGS. 5A-5B), a lower profile  28   b  that slopes upwardly at an angle β that exceeds 90 degrees measured from the plane of the sheet (see FIGS. 4A-4B), or a lower profile  28   a  that combines horizontal and sloped surfaces (see FIGS. 3A-3B). Furthermore, the protuberances may have an upper profile  26   a - c  that slopes downwardly at an angle α in the range of approximately 110 to 150 degrees measured from the plane of the sheet (see, e.g., FIGS. 3-5).  
         [0044]    It is further preferred that the protuberances  12  all thrust outwardly from a flat plane, as illustrated by plane  20  in FIGS. 3-7. The air-root pruning openings are defined by distal openings  16   a - c . In a particularly preferred embodiment shown in FIGS. 3A-3B, the protuberances begin as square-shaped proximal openings  14   b  one to two inches wide by one to two inches tall (but various squares or rectangles would work as well and the size of the squares or rectangles could be any of a range of sizes). The bottom of the resulting pyramidal protuberance defines the lower profile  28   b  and extends outwardly such that the lower profile is nearly horizontal and during use would be nearly perpendicular to the plane  20  of the sheet  10   b , typically parallel with the ground on which the resulting container  1  is setting. The top of the pyramidal protuberance defines the upper profile  26   a  and extends downwardly and outwardly at a steep angle α of approximately 150 degrees measured from the plane  20  of the sheet  10 . The two sides of the pyramidal-shaped protuberance extend outwardly to complement the top and bottom walls of the protuberance. The terminal ends of the four sides come together to create the distal opening for air-root pruning, which distal openings may be any shape or size desired, but a rectangular opening approx. {fraction (1/4)} inch wide by {fraction (3/8)} inch tall (see FIG. 3A) or a round opening approx. {fraction (3/8)} inch diameter works well (see FIGS. 7-8).  
         [0045]    The sheet design of the present invention takes advantage of the natural geotropism (the downward effect of gravity on roots) and outward extension of plant roots and provides superior capture and guidance of root tips to the distal protuberance openings for air-root pruning. The sheet design of the present invention is much more efficient, compared to other prior art container wall designs, in capturing root tips as they extend outwardly and downwardly and guiding the root tips to the air-root pruning openings. Further, with the present invention, the opportunity for root tips to avoid capture by the first outward protuberance encountered is minimized.  
         [0046]    Furthermore, the protuberances may have the same or different angles, shapes, or sizes in order to more closely follow the natural geotropism of a plant. For example, the protuberances in the portion of a sheet  10  outlying the upper region of the growth medium may employ lower profiles that are angled differently than the protuberances in the portion of a sheet  10  outlying the lower region of the growth medium.  
         [0047]    A preferred embodiment of the present invention employs a slight rise in the otherwise-horizontal lower profile of the protuberances about ⅔ the distance from the vertical plane  20  to facilitate the sheets being easily nested or stacked for storage and for fastening the overlapping edges of the sheet. Experimental uses of such an embodiment support a conclusion that root guidance is not compromised by this slight rise or lip as roots are, by this point, fully engaged in the protuberance and cannot escape.  
         [0048]    In a further embodiment of the present invention (not shown), the lower profile of the protuberances slopes downwardly such that it forms an angle α less than 90 degrees with plane  20 . This embodiment is less preferred, however, since it would be somewhat more difficult to form during manufacture, and to store and fasten. As mentioned above, a downward slope of the lower protuberance profile is not essential, and other embodiments such as those employing substantially horizontal lower profiles have shown considerable success in intercepting and directing the roots of a plant—even if the roots are extending outwardly but downwardly at angle of 60 degrees or more from the horizontal.  
         [0049]    By contrast, the more the lower profile  28  of the protuberances  12  slope upwardly, the greater the likelihood that the deflection or ricocheting of the root tip will be in some direction other than towards the distal opening  16 . It has been observed, however, that a slight upward inclination in the lower profile of the protuberances, especially near their distal openings as described above, will not divert the root tips from being air pruned. In fact, such a slight inclination aids in removal of the sheet from an injection molding die during manufacture, and facilitates easier overlapping or nesting when fastening the sheet edges together to form a cylindrical container. In particular, if the upward slope of the lower profile is formed deep into the projection of the protuberance near the distal opening, there is no opportunity for a root tip to do anything but continue on the path through the protuberance toward the distal opening.  
         [0050]    It is further preferred that the sheet  10  is formed of a thin, flexible plastic material and is adapted to be easily manually configured in a generally cylindrical shape, as shown in FIG. 8. Alternatively, sheet  10  could be formed of aluminum or another suitable metal, or of other materials such as a papier-mâché with some fiberglass or other fibers added to provide strength and durability.  
         [0051]    The sheet(s)  10  may be manufactured in various ways. For example, the sheets may be hot-pressed or injection-molded. Furthermore, the distal openings may be formed in the same step as the protuberances or the distal openings may be cut or otherwise formed in a step following formation of the protuberances.  
         [0052]    It is further preferred that the sheet be either: (a) provided with a fastener(s) to secure the edges of the sheet together when it&#39;s formed in the generally cylindrical shape (see, e.g., FIG. 7A); or (b) seamlessly formed in a generally cylindrical shape, such as by injection molding (see the seamless configuration of FIG. 8). The fasteners may include, without limitation, plastic rivets (indicated as  18  in FIG. 7A), staples, adhesive, snaps, clasps, hook and loop fasteners, mortise and tenon joints, and others. Such fasteners are described further in the Applicant&#39;s copending patent application Ser. No. 10/062,287 filed Jan. 31, 2002 and in U.S. Pat. No. 4,939,865 issued on Jul. 10, 1990, both of which are incorporated in their entireties herein by reference.  
         [0053]    The plurality of protuberances  12  on the sheet  10  preferably forms a lattice over at least a substantial portion of the sheet. It is further preferred that the protuberances are arranged in a close-packed configuration that employs little spacing between adjacent protuberances, which reduces the presence of areas in the sheet that might promote root ricocheting away from the protuberances. This is clearly illustrated in the embodiments of FIGS. 3-5.  
         [0054]    When the sheet is formed in the generally cylindrical shape by joining the edges of the sheet together, this may be achieved by overlapping one edge over another edge, and securing the edges substantially along the length of the edges (again, see FIG. 7A). Preferably, the overlapping of the edges is guided by the engagement of a lattice of root-directing protuberances in the region adjacent the one edge with a complementary lattice of root-directing protuberances in the region adjacent the other edge, as demonstrated in FIGS. 6 and 7.  
         [0055]    The sheet  10  generally defines a plane  20  in which a portion of each of the protuberances lies. Thus, in one embodiment, the sheet defines a plane in which the proximal opening  12  of each of the protuberances lies.  
         [0056]    In one embodiment, the sheet has an inner face and an outer face, and all the protuberances thrust outwardly in the direction of the outer face. The inner face includes the innersides of the planar portion of the sheet in this embodiment—if any—as well as the innersides of the plurality of protuberances. The outer face includes the outersides of the planar portion of the sheet—if any—and the outersides of the plurality of protuberances (see FIGS. 3A, 4A,  5 A,  7 , and  8 ). This may be contrasted with other embodiments wherein the plurality of protuberances are staggered such that adjacent protuberances thrust outwardly in opposite directions, i.e., some in the direction of the inner face and some in the direction of the outer face, but only the latter (outer-facing) set of protuberances have the distal openings for air pruning (not shown).  
         [0057]    In practice, as indicated in FIG. 8, plant containers employing the sheet  10  are placed on a root impervious surface (not indicated) which can be plastic, roofing paper, concrete or other surfaces, then filled with a growth medium  9  and a plant  5  is planted therein. As the plant grows, lateral root branching is maximized by the protuberances  12  as described above and as shown in the accompanying figures. At the end of the growth period prior to transplantation, root tips are thereby provided at all levels of the growth medium, i.e., in a plurality of the distal protuberance openings  16  disposed about sheet  10 . The plant is then transplanted from the container to a second, larger container (or the ground) by sheet  10  being unfastened at its fastened edges, and then carefully opened laterally outwardly so as not to damage the root tips, and removed. The space between the original and larger container (or the ground) is then filled with additional growth medium to surround exposed root tips, etc. Once removed, the sheet  10  can be reused to form another container of desired size.  
         [0058]    As will be understood, any sized sheet  10  can be utilized to make up a plant container according to the selected plant size. If during the growth of a plant prior to when it is transplanted, it is desirable to increase the size of the container in which the plant is being grown, one or more sheets  10  can be added to the original container sheet by fastening the edges of supplemental sheet(s) to those of the original sheet and placing additional growth medium into the container. Similarly, an original container may comprise one or more sheets fastened horizontally (making a container with a larger diameter) or vertically (making a container that is deeper).  
         [0059]    It will be understood from the foregoing description that various modifications and changes may be made in the preferred and alternative embodiments of the present invention without departing from its true spirit. For example, the present invention does not preclude the use of protuberances having no distal openings among the protuberances as described above. Such a combination would affect root trapping as well as root pruning, and is contemplated and encompassed by the present invention.  
         [0060]    This description is intended for purposes of illustration only and should not be construed in a limiting sense. The scope of this invention should be determined only by the language of the claims that follow. The term “comprising” within the claims is intended to mean “including at least” such that the recited listing of elements in a claim are an open group. “A,” “an” and other singular terms are intended to include the plural forms thereof unless specifically excluded.