Air root pruning container for growing a plant

A plant container has a base and a sidewall upwardly extending from the base. The sidewall includes stepped sidewall sections that each include a plurality of generally vertical sidewall panels having successively larger cross-sectional dimensions with distance from the base and horizontal ledges extending between an upper edge of an adjacent lower one of the sidewall panels and a lower edge of an adjacent upper one of the sidewall panels. The sidewall further includes a plurality of ribs, where each rib is formed between two of the stepped sidewall sections and extends inwardly across the ledges of the two stepped sidewall sections. Each rib has two legs that extend apart to form an outwardly-directed open channel. Holes are formed in the sidewall for air root pruning, where each hole is formed directly between a ledge and a leg of one of the ribs.

BACKGROUND

The present invention relates generally to an air-root-pruning container for growing a plant.

Background of the Related Art

Landscape plants and other plants intended to be transplanted have, for some time, been grown out-of-doors in containers above ground. Container-grown plants can be grown at a faster rate than those grown in the field, and because the roots of container plants are not severed or otherwise disturbed when the plants are transplanted, such transplanting can take place at any time during the year, not just during the early spring as required with bare root or bagged nursery stock.

A variety of containers for growing plants intended to be transplanted have been developed and used previously, beginning with metal cans having drainage openings punched in the bottoms and progressing to modern plastic containers. However, plants grown in conventional containers, especially woody plants, commonly experience problems such as spiral root growth and generally downward root orientation with little lateral root development.

In some containers having open bottoms, the roots become air-pruned when they reach the bottom, wherein the portion of each root extending into the air is killed by desiccation. However, the root tips are still at the bottom of the container rather than being laterally directed along the sides. It has been shown that the root growth of container-grown plants after being transplanted primarily involves the extension of roots which were present in the container at the time of transplanting as opposed to the development of new roots. Consequently, the number and the position of root tips present at the time of transplanting is very important to the rapid establishment and ultimate survival of container-grown plants.

BRIEF SUMMARY

One embodiment provides an air root pruning container for growing a plant. The air root pruning container comprises a base and a sidewall upwardly extending from the base. The sidewall includes a plurality of stepped sidewall sections, each stepped sidewall section including a plurality of generally vertical sidewall panels having successively larger cross-sectional dimensions with distance from the base and a plurality of generally horizontal ledges extending between an upper edge of an adjacent lower one of the sidewall panels and a lower edge of an adjacent upper one of the sidewall panels. The sidewall further includes a plurality of ribs, each rib formed between two of the stepped sidewall sections and extending inwardly across the plurality of generally horizontal ledges of the two stepped sidewall sections, wherein each rib has two legs that extend apart to form an outwardly-directed open channel. Still further, the sidewall includes a plurality of holes formed in the sidewall, each hole formed directly between one of the ledges and one of the legs of one of the ribs.

DETAILED DESCRIPTION

One embodiment provides an air root pruning container for growing a plant. The air root pruning container comprises a base and a sidewall upwardly extending from the base. The sidewall includes a plurality of stepped sidewall sections, each stepped sidewall section including a plurality of generally vertical sidewall panels having successively larger cross-sectional dimensions with distance from the base and a plurality of generally horizontal ledges extending between an upper edge of an adjacent lower one of the sidewall panels and a lower edge of an adjacent upper one of the sidewall panels. The sidewall further includes a plurality of ribs, each rib formed between two of the stepped sidewall sections and extending inwardly across the plurality of generally horizontal ledges of the two stepped sidewall sections, wherein each rib has two legs that extend apart to form an outwardly-directed open channel. Still further, the sidewall includes a plurality of holes formed in the sidewall, each hole formed directly between one of the ledges and one of the legs of one of the ribs.

The plurality of ribs may include a plurality of asymmetric ribs, wherein each asymmetric rib has a first of the two legs that forms a first angle relative to the container sidewall section adjacent the first side of the asymmetric rib and a second of the two legs that forms a second angle relative to the container sidewall section adjacent the second side of the asymmetric rib. Although the container sidewall is curved in some embodiments, the angle of a leg relative to the container sidewall can be measured relative to a tangent line of the container sidewall at the point where the leg is formed to the sidewall section. In one option, the first and second angles are more than 20 degrees different. In a preferred option, the first angle is about 90 degrees. Furthermore, the second angle may be between about 20 and about 70 degrees.

Where the air root pruning container includes a plurality of asymmetric ribs, the plurality of asymmetric ribs may include a first asymmetric rib and a second asymmetric rib that has at least one of the first and second angles that is different than the first and second angles of the first asymmetric rib. Any number of different asymmetric ribs may be included, and those different asymmetric ribs may differ in their first and second angles. In a preferred option, the second asymmetric rib may be a mirror image of the first asymmetric rib.

Each of the holes is formed in the sidewall directly between one of the ledges and one of the legs of one of the ribs. In other words, each hole is located where one of the ledges intersects with one of the legs of one or the ribs. In a preferred option, each hole may include a first portion that extends into a given one of the horizontal ledges and a second portion that extends into a given leg of a given one of the ribs. Such a hole may be formed with a rotary drill bit directed at the intersection of the ledge and the leg of the rib. Locating each hole partially in the ledge and partially in the rib facilitates air root pruning of roots growing laterally along the ledge as well as roots growing downwardly along the rib.

Embodiments that include a first hole formed partially in a first leg of a given one of the ribs and a second hole formed partially in a second leg of the given one of the ribs will preferably have the first and second holes separated by a distance greater than 0.63 centimeters (¼ inch). More specifically, if the first and second holes are aligned on opposing legs of a given one of the ribs, the first and second legs of the given one of the ribs should extend apart sufficiently to separate the first and second holes by a distance greater than 0.63 centimeters (¼ inch). The distance between the first and second holes is more preferably greater than about 1.26 centimeters (¼ inch). The separation between aligned or adjacent holes facilitates air root pruning, while reducing the likelihood of a root exiting the container and its growth medium through the first hole and re-entering the container and its growth medium through the second hole.

The stepped sidewall sections include a plurality of generally vertical sidewall panels having successively larger cross-sectional dimensions with distance from the base and a plurality of generally horizontal ledges extending between an upper edge of an adjacent lower one of the sidewall panels and a lower edge of an adjacent upper one of the sidewall panels. The upper edge of the plurality of sidewall panels may define a pitch line that slopes outwardly away from a central axis of the container with increasing distance from the base. In one example, two or more of the generally vertical sidewall panels in each stepped sidewall section may have the same height, and two or more of the generally horizontal ledges may have the same depth. Each of the plurality of ribs preferably extends inwardly beyond the pitch line.

The plurality of generally vertical sidewall panels may each be positioned about a common center line. For example, the plurality of generally vertical sidewall panels may each have a radius about a central axis of the container, such that the successively larger cross-sectional dimensions of the generally vertical sidewall panels include a successively larger radius.

The base may include a plurality of radial ribs. In one embodiment, each radial rib in the base may form a continuation of one of the ribs in the sidewall, wherein each radial rib has first and second legs that extend apart to form an outwardly-directed open channel. Each of the radial ribs may also include a first hole in the first leg adjacent the sidewall and a second hole in the second leg adjacent the sidewall.

The air root pruning container is preferably formed by blow molding followed by the drilling of the plurality of holes. The air root pruning container may have a plane of symmetry, wherein the sidewalls do not include any backslopes relative to the plane.

Embodiments of the air root pruning container may further include a plurality of outwardly extending, hollow handles formed in the sidewall, wherein the handles are spaced about a perimeter of the sidewall at a distance from the base that is further than the upper-most one of the plurality of ledges.

FIG. 1is a cross-sectional side view of a blow molding apparatus10for forming a workpiece20that includes two plant containers17,18. The mold12includes a left half11and a right half13that are moved together horizontally in the direction of the arrows14. Accordingly, the two halves11,13engage along an interface15to leave a cavity16in which a workpiece is formed. In the configuration shown, the cavity16includes an upper portion17that will form a first plant container and a lower portion18that will form a second plant container each time the blow molding apparatus10is used. Note that the upper portion17is inverted relative to the lower portion18. Accordingly, the left side11of the mold12includes an impression of one half of each container portion17,18and the right side13of the mold12includes an impression of the other half of each container17,18. The work piece from the blow molding apparatus10must be cut apart along the mid-section of the work piece.

The blow molding apparatus10delivers a softened plastic material between the two halves11,13of the mold12and the mold is closed. The softened plastic material is delivered into the mold12through an annular chamber19as a tube about an air nozzle20. When the mold12is closed (position shown), air or other gas is delivered into the tube of softened plastic under pressure to force the softened plastic outwardly to engage the surfaces of the mold12.

Once the softened plastic has been expanded into the desired form defined by the mold12, the workpiece is solidified by cooling the mold12. The mold12may be cooled by flowing water through cooling channels (not shown) formed within the mold halves11,13. Then, after the mold has cooled, the mold halves11,13are separated and the workpiece is removed.

Blow molding is advantageous, because there is only minimal outward pressure on the mold12and there is no inside tool or mold required. Furthermore, the mold12for a blow molding apparatus10can be machined of aluminum, which is less expensive, easier to manufacture, and more tolerant of temperature cycling than is injection molding. However, since the two halves of the mold are moved in opposite directions to open, any internal offsets must be shaped and positioned such that the part can be removed and is not torn or damaged as the mold opens. Specifically, there should be little or no backslopes or offsets to hinder or prevent release of the part from the mold. The asymmetric ribs described herein allow the air root pruning container to be blow molded and easily released from the mold as the two halves of the mold are separated to open.

FIG. 2is a cross-sectional of the blow mold12taken along line2-2inFIG. 1. The two mold halves11,13include interior surfaces22that define the cavity16, which forms the shape of the resulting workpiece20(seeFIG. 3). The mold halves11,13show an example of the angular positioning of features24that will form handles and other features26A-F that will form ribs around the perimeter of the cavity16. With the features24,26A-F positioned and shaped as shown inFIG. 2, each mold half11,13does not have any backslopes that would prevent opening of the mold12after the workpiece has been formed.

In the non-limiting example ofFIG. 2, the blow mold will form four handles and six ribs. The four handles may be formed with even (90 degree) spacing about the circumference of the plant container, such as with two opposing handles formed along the interface of the mold halves and another two opposing handles formed in the middle of each mold half. The six ribs may be formed with even (60 degree) spacing about the circumference of the plant container. In a preferred configuration, certain ribs may be asymmetric and certain ribs may be symmetric, and each rib may be appropriately positioned, to avoid having backslopes at any point in the mold that would hinder both mold-halves from separating easily.

In the example shown, the features26A,26C,26D,26F will form asymmetric ribs and the features26B,26E will form symmetric ribs. The feature26A has first side28A (to form a first leg of a rib) that is perpendicular to the adjacent surface of the cavity16(which forms a sidewall section) (i.e., at a 90-degree angle to the tangent at the point of intersection). The feature26A also has a second side29A (to form a second leg of the rib) that is at an angle of about 20 degrees relative to the adjacent surface of the cavity16(which forms a sidewall section) (i.e., at a 20-degree angle to the tangent at the point of intersection). By contrast, the feature26B has first side28B (to form a first leg of a rib) that is angled relative to the adjacent surface of the cavity16(which forms a sidewall section) (i.e., at about a 60-degree angle to the tangent at the point of intersection) and a second side29B (to form a second leg of the rib) that is also angled at the same angle relative to the adjacent surface of the cavity16(which forms a sidewall section) (i.e., at about a 60-degree angle to the tangent at the point of intersection).

Note that the feature26A will form an asymmetric rib that is different than the asymmetric rib formed by the feature26C. While the angle of the side28C may be the same as that of side29A and the angle of the side29C may be the same as that of side28A, the orientation of the feature is reversed. Both features avoid any backslopes that would hinder or prevent the mold halves11,13separating in the direction of the arrows14. Furthermore, the features26A,26C form asymmetric ribs that are mirror images of the asymmetric ribs formed by the features26F,26D relative to the plane defined by the interface15between the two mold halves11,13. The plant container is not limited to any particular number of ribs and is not limited to any particular number of asymmetric ribs that are different.

While the mold12will form a plant container having a horizontal cross-section that is generally circular, except for the ribs and the handles, a mold could be made to form a plant container having a horizontal cross-section that is ovoid or a regular polygon, such as a rectangle or hexagon.

FIG. 3is a side view of a workpiece20that is formed by the blow molding apparatus10. The workpiece20may be cut in half along the dotted line21to separate the workpiece into two plant containers30.

FIG. 4is a perspective side view of the outside of an air root pruning container30for growing plants. The container30includes a base32and a sidewall34upwardly extending from the base32. The sidewall includes a plurality of stepped sidewall sections40and a plurality of ribs50, where each rib50is formed between two of the stepped sidewall sections40. Each stepped sidewall section40includes a plurality of generally vertical sidewall panels42having successively larger cross-sectional dimensions with distance from the base32and a plurality of generally horizontal ledges44extending between an upper edge of an adjacent lower one of the sidewall panels42and a lower edge of an adjacent upper one of the sidewall panels42. Each rib50extends inwardly into the container30across the plurality of generally horizontal ledges44of the two adjacent stepped sidewall sections40. Furthermore, each rib50has two legs52,54that extend apart to form an outwardly-directed open channel56.

A plurality of holes60are formed in the sidewall in specific locations to facilitate air root pruning. For example, each hole may be formed directly between one of the ledges44and one of the legs52,54of one of the ribs50. In one option, each hole may be drilled such that the hole removes a portion of the horizontal ledge and a portion of the rib. In a further option, each hole may be positioned so that about one half of the hole removes a portion of the horizontal ledge and about one half of the hole removes a portion of the rib. The holes are preferably positioned and sided to avoid removing any of the curved outer wall of the container. For example, the diameter of each hole is preferably no greater than the depth of the ledge.

A further hole62is preferably drilled into each of the two legs of each radial rib in the base, with this hole located along the sidewall and base. The hole in each leg preferably has a diameter that is about half the height of one leg of the hollow base rib. The remaining upper portion of each radial rib will strengthen the container.

Handles46are formed near the top of the container30, but below an upper rim48. The outwardly-extending handles46are preferably hollow, forming a cavity that opens inwardly. However, since the handles are toward the top of the container30, the cavity in the handles46is not expected to engage many roots or have any significant effect on root development of a plant.

FIG. 5Ais a top view of the air root pruning container30ofFIG. 4. In this top view, the handles46are shown spaced about the perimeter of the container and extending outwardly beyond the rim48. The base32includes radial ribs36A-F that extend radially outwardly from a central axis38of the container. Each of the radial ribs36A-F preferably include two legs37,39that extend apart to form an outwardly-directed (downwardly-directed) open channel.

The sidewall of the container extends upwardly from the base32and includes a plurality of stepped sidewall sections40(six shown) and a plurality of ribs50A-F (six shown), where each rib50A-F is formed between two of the stepped sidewall sections40. Each stepped sidewall section40includes a plurality of generally vertical sidewall panels42having successively larger cross-sectional dimensions with distance from the base32and a plurality of generally horizontal ledges44extending between an upper edge of an adjacent lower one of the sidewall panels42and a lower edge of an adjacent upper one of the sidewall panels42. Each rib50A-F extends inwardly toward the middle of the container30and also extends across the plurality of generally horizontal ledges44of the two adjacent stepped sidewall sections40. Furthermore, each rib50A-F has two legs52,54that extend apart to form an outwardly-directed open channel. Preferably, each rib50A-F aligns with a radial rib36A-F and forms a continuous rib structure with legs52,54aligned with legs37,39, respectively, to form continuous leg structures.

A plurality of holes60are formed in the sidewall in specific locations to facilitate air root pruning. For example, each hole (48holes are shown) is formed directly between one of the ledges44and one of the legs52,54of one of the ribs50.

FIG. 5Bis cross-sectional side view of the air root pruning container30taken along line5B-5B inFIG. 5A. This view shows how the ribs50A,50B,50E,50F extend across each of the ledges44and how the radial ribs36E,36B extend upward. Furthermore, the ribs50E,50B are shown formed as a continuous structure with the radial ribs36E,36B. Still further, the sidewall panels42and the ledges44are shown to define a pitch line49(shown in dashed lines) that represents the overall pitch of the steps in the stepped sidewall sections between the ribs. The pitch is affected by the depth of the ledges44(for example, depth diand depth dj) as well as the height of the sidewall panels42(for example, height hiand height hj). The ribs50A-F preferably extend inwardly beyond the pitch line49, as shown, and the legs of each rib are formed to their respective adjacent stepped sidewall section.

FIGS. 6A and 6Bare partial perspective views of the inside of the air root pruning container.FIG. 6Aillustrates the relationship between the stepped sidewall sections40and the rib50A, which is an asymmetric rib. The stepped sidewall sections40extend upward from the base32and include a plurality of sidewall panels42and a plurality of ledges44. The sidewall panels42are substantially vertical, wherein each panel42has a greater radius than the panel42below it (in the direction of the base32). The ledges44are substantially horizontal and connect one sidewall panel to the next to form steps on the inside of the container rising from the base32.

InFIG. 6A, the ledges44of a first sidewall section40(as shown on the left of the rib50A inFIG. 6A) intersect the leg54of the rib50A at each location58and the ledges44of a second sidewall section40(as shown on the right of the rib50A inFIG. 6A) intersect the leg52of the rib50A at each location59. Furthermore, the rib50A and the radial rib36A form a continuous rib structure. Accordingly, the rib structure extends across the corner between the base32and the sidewall section40.

InFIG. 6B, holes60for air-root pruning have been formed in the container sidewall at the locations58,59(seeFIG. 6A) wherein the ledges44intersect the legs52,54of the rib50A. Each hole60has a first portion that extends along the horizontal ledge44away from the rib50A and a second portion that extends up the rib50A from the horizontal ledge44. Where the hole is formed by drilling into the plant container, about half of the drilled hole may remove material from the horizontal ledge adjacent the intersection of the rib and the ledge, and about half of the drilled hole may remove material from the rib above the intersection of the rib and the ledge. Furthermore, holes62are formed in the legs of the rib structure aligned with the base32and the lowest sidewall panel42.

The holes formed on opposing sides of a rib should have sufficient spatial separation to allow effective air-root pruning due to the air gap between the two sides of each rib. This configuration facilitates air root pruning while also allowing a root ball to slide right out of the container without restriction.

With air root pruning holes60formed in the container sidewall as described, roots (illustrated as un-numbered arrows inFIG. 6B) of a plant growing in the plant container will grow out, intersect the horizontal ledge44, and be directed either left or right. If the holes60were formed entirely in the horizontal ledge, some roots would avoid the opening and continue extending. Accordingly, holes formed solely in the horizontal ledge44may have only minor effectiveness for air root pruning. By forming the holes partially in the horizontal ledge and partially in the vertical wall of the rib, roots that are not sufficiently affected by geotropism to enter the part of the hole in the horizontal ledge will extend onward to enter the part of the hole formed in the rib and will be effectively air root pruned. Roots may also enter the hole after extending along a sidewall panel42of a leg of the rib50A.

Furthermore, the ribs50A,36A must be sufficiently wide so that a root cannot exit the plant container through a first hole in a first side of the rib, then re-enter the plant container through a second hole in a second side of the same rib. The distance between the holes on opposing sides of a rib is preferably at least 0.63 centimeters (¼ inch), more preferably at least 1.26 centimeters (½ inch), and may be even greater.

FIG. 7Ais a schematic diagram illustrating the shape of an asymmetric rib50A formed in the sidewall of the air root pruning container30. In this example, the asymmetric rib50A has a first leg54that is near perpendicular to the container sidewall and a second leg52that slopes out from the inner edge of the rib toward the container sidewall. Note how the legs54,52form the hollow or open channel56. The legs54,52are separated by a sufficient distance to form an outward-facing air space between the two legs of the rib that facilitate air root pruning.

The first leg54may be characterized by an angle θ1between the leg54and a line T1that is tangent to the container sidewall at the point where the leg54connects with the (left) sidewall panel42. In this illustration, the angle θ1is about 90 degrees. Similarly, the second leg52may be characterized by an angle θ2between the leg52and a line T2that is tangent to the container sidewall at the point where the leg52connects with the (right) sidewall panel42. In this illustration, the angle θ1is about 25 degrees.

FIG. 7Bis a schematic diagram illustrating the location of air root pruning holes60relative to the asymmetric rib ofFIG. 7A. The holes60are partially formed in the ledges44and partially formed in the legs52,54of the rib50A.

FIG. 8Ais a schematic diagram illustrating the shape of a symmetric rib50B formed in the sidewall of the air root pruning container30. The diagram here is similar to that ofFIG. 7A, except that the rib50B is symmetric. Accordingly, the first leg54may be characterized by an angle θ1between the leg54and a line T1that is tangent to the container sidewall at the point where the leg54connects with the (left) sidewall panel42, and the second leg52may be characterized by an angle θ2between the leg52and a line T2that is tangent to the container sidewall at the point where the leg52connects with the (right) sidewall panel42. For a symmetric rib, such as rib50A, the angle θ1will be equal to the angle θ2, although the angles may vary. As shown, both angles θ1and θ2are about 70 degrees.

FIG. 8Bis a schematic diagram illustrating the location of air root pruning holes60relative to the symmetric rib ofFIG. 8A. The holes60are partially formed in the ledges44and partially formed in the legs52,54of the rib50A.

The corresponding structures, materials, acts, and equivalents of all means or steps plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. Embodiments have been presented for purposes of illustration and description, but it is not intended to be exhaustive or limited to the embodiments in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art after reading this disclosure. The disclosed embodiments were chosen and described as non-limiting examples to enable others of ordinary skill in the art to understand these embodiments and other embodiments involving modifications suited to a particular implementation.