GB2550189A - Hydroponic growing method - Google Patents

Abstract

A hydronic growing method which comprises depositing plant matter and a growth substrate within a plant tray 100 which has one or more recesses for holding the plant matter; placing the plant tray on a stacking tray 110 having a base and one or more upwardly projecting walls dimensioned so as to extend above the plant tray's upper surface when it is located on the stacking tray; repeating the steps using second plant and stacking trays, and stacking the second stacking tray on top of the first stacking tray so that a gap g is left between the upper surface of the first plant tray and the base of the second stacking tray; storing the stacked trays for an initial stage growing period in which plant growth can extend into the gap between stacked trays; and unstacking the stacking trays and locating the first and second plant trays on one or more hydroponic flood table(s) for a second stage growing period.

Description

Hydroponic Growing Method FIELD OF THE INVENTION

The present invention relates to a hydroponic growing method. BACKGROUND OF THE INVENTION

The hydroponics industry is growing year on year. It is becoming increasingly common and indeed necessary for nations of the world to grow fresh produce locally to feed their populations . A common method of growing plants involves an NFT (Nutrient Film Technique) system. An NFT system is a recirculating hydroponic system that consists of growing channels or trays over which a nutrient solution is constantly pumped across, creating a nutrient film into which the roots grow. Plants are often started in stone wool cubes and placed on the growing channels. The solution is recirculated from a main tank. Other methods and apparatuses are known.

One such other method is known as "flood and drain" or "ebb and flow". The method involves placing plants onto a flood table (a bath-like structure having a base and side walls) and pumping a nutrient solution into the flood table to flood the plants, submerging the roots. The pump is turned-off and the solution drained away. This cycle is repeated periodically, often using a timer to control the length and period of the cycles automatically. As the plants grow, the number of floods is usually increased.

Large scale hydroponic systems require a considerable amount of land as plants are traditionally laid out in channels along a horizontal plane over a large area. In general, the greater the amount of produce required, the greater the area of the land needed to grow the produce. Consequently, urban areas rely on fresh plants and edible produce to be delivered from the rural, often distant, farming areas. The expanse of farming area required means that fresh produce is generally not grown on a commercial scale within urban areas and cities. This is particularly the case in built-up cities around the world were open space is limited and at a premium.

Restaurants within cities and urban areas require daily deliveries of fresh produce. Supermarkets also require regular large deliveries requiring vast transport networks and logistics .

Vertical tier systems are known which allow fresh produce to be grown in vertical tiers of shelving, reducing the amount of space required.

Applicant's patent application publication number WO2015140493 provides an improved vertical growing system for growing inter alia plants, which has a flexible modular structure to alleviate the spatial limitations of other systems and which allows sections of tiered shelving structure to be moved and re-positioned during, and without interfering with, the growing cycle. The term "growing system" is intended to include any system that provides water or other nutrient fluid to plants growing within the system. This includes NFT systems as well as flood and drain systems.

The term "plants" is intended to include edible leaves, such as lettuces and herbs.

However, even with vertical tiered systems, significant space is required before and after use (e.g. in the initial stage of germinating from seed and/or storage prior to packaging).

It is therefore an aim of this invention to provide an improved hydroponic growing method and apparatus for use in such a method.

SUMMARY OF THE INVENTION A first aspect of the invention provides a hydronic growing method, comprising: (i) depositing plant matter and a growth substrate within a plant tray which comprises an upper surface and one or more recesses for holding the plant matter; (ii) placing the plant tray on a stacking tray having a base and one or more upwardly projecting walls dimensioned so as to extend above the plant tray's upper surface when it is located on the stacking tray; (iii) repeating steps (i) and (ii) using second plant and stacking trays, and stacking the second stacking tray on top of the first stacking tray so that a gap is left between the upper surface of the first plant tray and the base of the second stacking tray; (iv) storing said stacked trays for an initial stage growing period in which plant growth can extend into the gap between stacked trays; and (v) unstacking the stacking trays and locating the first and second plant trays on one or more hydroponic flood table(s) for a second stage growing period.

The method may further comprise, subsequent to step (v), the step (vi) of flooding the or each flood table(s) with a volume of nutrient-containing liquid so that its level is above that of the plant trays' upper surface to water the plant matter and growth substrate, and then draining the flood table, as part of a second stage growing period.

The method may further comprise the step (vii) of repeating step (vi) for subsequent flood and drain cycles over the second stage growing period.

The method may further comprise, subsequent to step (vi) or claim (vii), placing each plant tray on a respective stacking tray and stacking the stacking trays one on top of the other.

Each plant tray may comprise plural, non-draining recesses sunken into the upper surface.

The growth substrate may be a layer of fibrous biodegradable material, e.g. a carpet.

Each stacking tray may comprise a base of greater area than that of the plant tray.

The or each wall of the stacking tray may project upwardly by more than twice the depth of the plant tray. The or each wall may project upwardly by more than three times the depth of the plant tray.

The or each wall of the stacking tray may be arranged to completely surround an internal base area within which the plant tray sits flat in use.

The or each wall of the stacking tray may have, at or near its upper edge, a surface shaped so as to receive the external base of another stacking tray in such a way as to limit lateral movement when stacked.

Step (v) may comprise locating the first and second plant trays on one or more hydroponic flood table (s) which are part of a vertical tiered flood and drain system. A further aspect of the invention provides a hydroponic growing method, comprising: (I) providing multiple plant trays, each plant tray comprising an upper surface and a plurality of sunken, nondraining recesses within which are received plant seeds or germinating plant seeds in or adjacent a substrate; (II) moistening the substrate; (III) placing each plant tray within a respective stacking tray which comprises a base larger than the plant tray and which has one or more surrounding walls which extend above the plant tray upper surface; (IV) stacking the stacking trays one on top of the other and storing them for a growth period in which the plants grow into the gap left between the plant tray and the stacking tray stacked above it; (V) subsequently unstacking the stacking trays, removing the plant trays and locating them on a flood table of a flood and drain system which periodically floods the flood table with nutrified liquid to a level just above that of the plant trays before draining said liquid, promoting further growth. A further aspect of the invention provides a stacking tray configured for use in the method according to any preceding definition, comprising a base having one or more upwardly projecting walls of greater height than a plant tray it is configured to hold.

The stacking tray may have a non-draining base.

The stacking tray may have at or near the upper periphery of the wall(s) a shaped part dimensioned and arranged to receive the base of another stacking tray to limit its lateral movement when stacked. A further aspect of the invention provides apparatus configured for use in the method according to any preceding definition, comprising a plant tray having a plurality of recesses beneath an upper surface, and a stacking tray comprising a base of greater area than that of the plant tray with one or more upwardly projecting walls of greater height than the depth of the plant tray, so that there is a left a gap been the respective upper surfaces when the plant tray is located within the stacking tray.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described, by way of non-limiting example, with reference to the accompanying drawings, in which:

Figure 1 is a perspective view of a plant tray for use in a method according to the invention;

Figure 2 is a side-sectional view of a recess of the Figure 1 plant tray;

Figures 3a and 3b are side and top plan views of a stacking tray for use in the method according to the invention;

Figure 4 is a partial sectional view showing an optional engagement system between stacking trays when placed one on top of the other;

Figures 5a and 5b are side views of a stack of stacking trays before and after a growth period;

Figures 6a and 6b are perspective views of the plant trays when removed from their respective stacking tray and placed on, respectively, a flooding table, and tiered flooding tables;

Figure 7 is a side view of the stack after a flood and drain cycle;

Figure 8 is a perspective view of a vertical tiered section forming part of a vertical growing system constructed in accordance with a first embodiment useful for understanding the present invention;

Figure 9 is a close up view of part of tiered section of figure 8;

Figure 10 is an end view of the tiered section;

Figure 11 is a view of a drainage tank for use with the tiered section;

Figure 12 is a close of the top part of the tiered section; Figure 13 is a perspective view of a vertical tiered section forming part of a vertical growing system constructed in accordance with another embodiment, which is useful for understanding the invention;

Figure 14 is an end view of the tiered section of figure 13; Figures 15(a) to (c) are schematic illustrations of tracks of the system in plan view;

Figures 16(a) and (b) are schematic illustrations of how the sections can be moved to form paths there between; and Figures 17 (A) and (B) are schematic illustrations showing the water tank of the system;

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS A hydroponic growing method will now be described with regard to a "flood and drain", or "ebb and flow", setup employing particular apparatus.

Referring to Figure 1, a plant tray 100 is shown, comprising a metal or plastics sheet having a generally planar upper surface 101 and a lower surface 102. Within the upper surface 101 are formed a plurality of recesses 103, sunken into said surface, and can be of any shape or size, although circular recesses are shown herein. The recesses 103 define individual growing areas for receiving seeds, or germinating seeds. The recesses 103 in this case project beyond the lower surface 102 but in other embodiments can be shallower so that the lower surface remains substantially planar.

Figure 2 shows one recess 103 in cross-section, within which is placed a growing substrate 105, e.g. rock wall or a biodegradable fibrous material, e.g. biodegradable carpet. A seed 107 is typically buried within the substrate 105, or can be placed on or below it, and the substrate is moistened. The substrate 105 provides support for the roots as the seed germinates. It is often an inert material. In this case, individual disc-like substrates 103 are placed into each recess 103, but in other embodiments, a larger sheet can be laid over multiple recesses, with a seed placed in each recess location.

Referring to Figure 3a and 3b, a stacking tray 110 is shown having a base 112 and two upstanding walls 114 on opposite sides of the base to provide a generally U-shaped structure. In other embodiments, four walls are provided, i.e. to surround the base 112, and only a single wall might be used if circular. The internal surface area of the base 112 is shaped and dimensioned to be greater than that of the plant tray 100. The stacking tray 110 may be formed of metal, plastics or indeed any material. The height of walls 114 is approximately identical on both sides and greater than the depth of the plant tray 100 as indicated by the dotted lines. Accordingly, the plant tray 100 when located on the base of the stacking tray 110, as shown in phantom lines in Figure 3a, leaves a gap "g" between its upper edge and the upper extent of the walls 114 .

In the method, multiple stacking trays 110 are placed one on top of the other in a vertical stack. The base 112 of one therefore rests on the upper edges of the walls 114 of the one beneath. In other embodiments, the stacking trays 110 may be slightly trough-shaped, or, as indicated in Figure 4, have cut-outs 118 near the upper ends for receiving an appropriately-shaped base part 120 of the other stacking tray in order to limit lateral movement when stacked.

In the present growing method, the seeds 107 and substrate 105 are placed in respective recesses 103 of the plant tray 100. The plant tray 100 is placed in a stacking tray 110, as indicated in Figure 3a. The process is repeated with other plant and stacking trays 100, 110 which are stacked, one on top of the other, as shown in Figure 5a. The stacked tiers 130 are then placed in a growing room or other suitable environment to promote germination for a given initial time period. In this period, the gap "g" between the various sections allows upwards growth without interference from the upper level, and overall the stack 130 allows a greater number of plants to be catered for in a given floor footprint. See Figure 5b, showing how the plant 133 is not affected. Also, the stack 130 can be placed on a trolley 135 or the like for easy transportation to and from the growing room.

After the initial growing period, the stack 130 is moved to a flood and drain growing apparatus, or alternatively, each section of the stack 130 can be moved individually. Referring to Figure 6a, this generally comprises a flood table 140, being a bath with raised edges 142. A pump (not shown) is configured to flood the table 140 with a predetermined volume of nutrient liquid through an inlet 145. The volume is such as to just cover the depth of a plant tray 100 when located on the table 140 to provide nutrients to the plants 133, after which the pump ceases delivery. After a predetermined period subsequent to flooding, a drain 147 is opened to drain the liquid to a tank underneath (not shown) using gravity. Alternative flood and drain mechanisms and arrangements may be used.

As shown in Figure 6a, the flood table 140 may be dimensioned to receive multiple plant trays 100. Rollers (not shown) may be provided in the lower part of the flood table 140 to allow plant trays 100 to be moved over the table easily. Figure 6b shows a vertical tiered system employing multiple flood tables 140, one on top of the other, which in use may be supplied with water from a single pump and drained to a single tank for recycling and/or filtering and replenishment in a feedback cycle .

The "flood and drain" process is typically repeated for a further growing period depending on the stage of plant growth. The process is usually controlled using an electronic timer system which starts and stops the pump, and opens and closes the drain 147, in accordance with settings or a program. UV light may also be used in conjunction with the flood table 140 during this growth stage.

Again, the use of tiered flood tables limits floor space.

At the end of the "flood and drain" stage, the plant trays 100 are again placed within a respective stacking tray 110 and stacked one on top of the other as shown in Figure 7. The gap "g" is sufficient still to allow for the increased growth without interference. The stack can then be transported for storage and/or packing for onwards sale or transportation to customers .

The base of the plant trays 100, including the recesses 103, is closed, i.e. there are no drainage holes, to maintain moisture in the substrate 105 and prevent dripping when moving the trays 100 to the stacking trays 110. Similarly, the stacking trays 110 may have a closed base 112.

Overall, it will be apparent from the foregoing that large numbers of plants can be grown, over a given footprint area, and can be transported in bulk between locations, e.g. growing rooms and flood tables. Further advantages are provided by performing the given method in association with a vertical tier growing apparatus, e.g. as described in WO2015140493 the entire contents of which are incorporated herein by reference. For completeness, we discuss this apparatus, and variations thereof, in the following.

Figure 8 illustrates an assembled tiered section 1 of a vertical tiered growing system, in this case an NFT system but it can be a "flood and drain" system, as briefly introduced above, and a further embodiment of which is described with reference to Figures 13 and 14 below. The overall system includes a plurality of such sections. The section 1 comprises a framework of interconnecting vertical and horizontal beams (2 and 3 respectively), which are separately supplied for assembly on-site, or can be supplied partially or fully-assembled depending on the space in the storage container. Angled beams 4 are provided at the base to provide strength to the base of the framework. A tiered array of elongate plant trays 5 extend longitudinally along the frame work resting across the horizontal beams 3.

The framework beams 2, 3 are constructed from aluminium or other suitable strong but lightweight material. Plastics material can be employed.

As can be seen in Figure 9, the horizontal beams 3 are connected to the vertical beams 2 through jointed clamps 6, the height of which can be altered to lower or heighten any tier level within the section 1 without having to deconstruct the entire framework.

Each plant tray 5 is generally made from plastic and has a hollow rectangular form. Apertures 7 are provided uniformly along each tray 5 in which are received plant roots or seedlings which grow into plants such as, for example in the case illustrated in the top tier of Figure 12, lettuce. In use, a flow of nutrient is directed into and along each tray 5.

One end of the section (shown in Figure 9) has a secondary frame of pipe work 9. Tubing 10 links the end of each tray 5 with the pipe work 9 to provide a closed system through which nutrient can flow between the trays 5 and the pipe work 9 for recirculation across the tiers of trays 5.

Artificial light tubes 11 and respective electrical fittings are provided, for connecting to the frame work such that they extend above, and generally parallel to, each tray 5. The artificial light may be generated from, for example, LEDs. The light tubes 11 are clamped to, and extend downwardly from, the horizontal beams 3 of the framework. As can be seen in Figure 9, the electrical connection 12 to each light tube 11, linking the light tube 11 to a power source remote from the section, is flexible such that the power link remains intact and connected when the height of any shelf within the section 1 is adjusted. All electrical connections 12 are provided in modular form, for interconnection to the appropriate other connections using standard plug and socket connectors.

The other end of the tiered section 1 is illustrated in Figure 10. Drainage pipe work 13 is connected to this end of the section 1. The drainage pipe work 13 has a plurality of outlet pipes 14 connected in turn to the end of each tray 5.

Once assembled, the trays 5 extend across each tier of the section 1 at a slight angle such that they extend slightly downwardly towards the end of the section with the drainage pipe work 13 (i.e. the end shown in Figure 10) . Consequently excess nutrient flows along to the trays 5 into the drainage pipe work 13 to be dispensed into a drainage tank 15.

The drainage tank 15 is preferably housed within the floor system 112, 123, under its upper surface, and includes a pump 16 to pump nutrient back through tubing 17 and back into the trays 5 for recirculation (see Figure 12) . The drainage tank 15 can be an integral part of the floor system 112, 123, beneath one of its apertures, or can be provided as a separate component for fixing inside the floor system.

As can be seen in Figure 10, the system is arranged in this case to locate onto a track assembly 18 (refer to Figure 6 above) which is secured to the floor system 112, 123. Only part of the track assembly 18 is shown in Figure 10. The entire track 18 has a grid like form allowing individual sections to be moved sideways along the grid towards or away from each other.

The track 18 extends across substantially the entire base footprint of the system. In practice a number of tiered sections 1 are located on the track assembly 18 and each section is movable along the track 18 to alter their position relative to each other. This allows a path to be opened between any two sections 1 to allow access the plants in any section 1 where necessary. When access is no longer required to the side of a particular section 1, the neighbouring section can be moved across the track assembly 18 towards and against its neighbour thereby closing the gap whilst at the same time opening up path between another section 1 and its neighbour .

The fact that each section 1 is individually movable along the track assembly 18 means that the overall footprint area of the track for the entire system (including a number of sections) only needs to incorporate a single path width thereby significantly increasing the number of the tiered sections 1, and hence the grow able area within the system, within any defined location.

Referring to Figure 15(a), which is a plan view of the floor system, in some embodiments the track may comprise first and second parallel rails 34, spaced apart. Each section 1 (not shown in Figure 15) is configured to slide or roll over the rails by respective spaced-apart sets of wheels, casters, rollers or sliders. A handle may be provided on the end of each section 1 to assist the movement. Figure 15 (b) shows that the track may comprise one or more additional rails 36. Figure 15(c) shows a grid-like system 38 of rails, including one or more rails transverse to the longitudinal rails shown in Figures 15(a) and (b) for stability in terms of preventing the rails moving towards or away from each other.

The rails of the track can be of any form, e.g. cross-sectional profile. Figures 16(a) and 16(b) show in schematic view how the overall footprint area of the enclosed growing area can be minimised, by using the aforementioned track system. In Figure 16(a) the space 40 represents both an access path for the adjacent section 1 (G) , and also a void into which said section (G) can be moved to provide access to the next section (F) . It follows that multiple sections 1 can be moved as required, and Figure 16(b) shows how movement of multiple sections (C, D, E, F, G) along the track rails creates a new path 42 for access to the adjacent sections (B, C) .

Furthermore, the fact that individual lighting and water assemblies supporting plant growth on each section 1 are carried, when assembled, on that section 1 itself means that the section 1 can be moved sideways along the track 18, e.g. as indicated in Figure 16, during a plant growing cycle without requiring disconnection of the lighting or nutrient systems which would otherwise disrupt and adversely affect growth of the plants. Moreover, each individual lighting and nutrient fluid assemblies are connected to a centralized source with flexible linkages which are able to accommodate an increase or decrease in length as the section 1 is moved towards or further away from the source. The centralised power source and warer/nutrient storage (neither shown) feeding the overall system may, for example be located in within the roof structure of the building within which the system is installed and would be connected to each section 1 through individual flexible linkages extending downwardly from the source for connection to the appropriate section.

In an alternative embodiment (not shown) each section may carry its own power source, such as a battery, and a storage tank for nutrient fluid.

Whilst the drainage tank 15 shown in Figure 11 is shown to be width of a single section 1, it envisaged that in some embodiments the tank 15 can be elongated so that its overall length would be sufficient to accommodate sideways movement of the section 1 along the track 18 whilst retaining the ends of the drainage pipes 13 within the confines of the tank walls 19.

In an alternative embodiment the drainage tank takes the form of a single trough like structure that extends along the entire side perimeter of the track, but, again, beneath the hollow floor system, such that the drainage pipes 13 of each section remain within the confines of the walls of the trough, even when a section is moved to the extremity of the track. An example of this is described later on.

Figures 13 and 14 illustrate a different tiered section 20 for use in a vertical drainage system, this time working on the flood and drain principle. In flood and drains systems, sometimes known as ebb and flow, the entire root zone is periodically flooded with nutrient solution before it dries out. This is done with a timer on a pump from a main nutrient tank usually located directly below the flood tray. The root zone is flooded for short periods of time (between 10-15 minutes). The interval between floods will depend on plant size and medium used (stone wool or expanded clay pebbles). As with the embodiment previously described, the overall system would include a plurality of such sections. The section 20 comprises a framework of interconnecting vertical and horizontal beams (21 and 22 respectively). The framework beams 21, 22 are constructed from aluminium or other suitable strong but lightweight material.

The horizontal beams 22 are connected to the vertical beams 21 through jointed clamps 23, the height of which can be altered to lower or heighten any tier level within the section 20.

Three elongate supporting arms 24 extending longitudinally through the section 20 at each tier level. The arms 24 provide supports for plant trays 25 which extend perpendicularly across the framework at each tier level.

Each arm 24 is provided with a roller mechanism 26 extending along the entire length of each arm 24 such that the trays 25 can be easily dragged along the longitudinal axis of the section 20 from one end to the other. The trays 26 may be manually moved along the rollers 2 6 or the movement may be automated.

As can be seen best in Figure 14, drainage channels 27 extend along the length of one side of the section 20. The drainage channels 27 provide a path for flow of nutrient from the tray 25 after it has been flooded, during the drainage stage. The end of the drainage channels extend over an aperture, or multiple apertures, in the floor system, over one or more drainage tanks (not shown).

Like in the first described embodiment of the growing system, the section 20 is one of several within the system that is secured to a floor track allowing movement of the sections 20 to open and close walkways therebetween as has previously been described.

Like with the first described embodiment, the lighting and nutrient systems for any given section 20 are carried on that section 20 such that any given section 20 can be moved along the track without the need for disconnection of the systems thereby allowing that section to be moved during the growth cycle of the plants.

The vertical tiered sections described above are designed for use in an overall system comprising a number of such sections and a floor track on which each section is mounted. The system would also include means to connect the centralised fluid and electricity supplies to the nutrient and lighting assemblies of each section.

Referring to Figures 17(a) and 17(b), there is now described an example of the above-mentioned elongated tank. The tank 50 has a length, in this case, that extends substantially the length of side-by-side sections 1 as well as extending along the gap 40. The tank 50, sits within the hollow part of the floor system, i.e. beneath its upper surface, beneath an elongated aperture. The drainage pipes 13 of each section 1 (shown in section) are supported overhanging the tank 50 so that fluid exiting the lower ends drains into the tank, and the aforementioned sideways movement of the sections does not result in spillage. Indeed, the overhanging pipes 13 can be level with, or below, the upper perimeter wall of the tank 50 to minimise splashing.

The Figure 17 tank 50 is also different in that it is divided into two distinct liquid-carrying parts, namely a drainage portion 52 and a fresh liquid portion 54 divided by an intermediate lengthwise wall 56. The drainage portion 52 has a sloping floor in order to urge using gravity the collected liquid towards one end where it can be removed from the tank 50, whether permanently, or for processing by a filtering/recycling system. The flow of draining liquid is indicated by the arrows to an exit aperture 60. The fresh liquid portion 54 is covered by a top wall 62; liquid is fed-in from a mains or other source through an inlet pipe 64 and exits as and when required through outlet pipe 66 which is connected to a pump that transmits the liquid to the individual sections 1. The incoming liquid may be fresh water or nutrient-containing liquid. Inspection covers 70 are provided to enable access to the fresh liquid portion 54, whether for checking levels and/or adding chemicals. Thus, both drainage and fresh liquid storage is enabled in a combined, compact and convenient unit within the growing room 30. The tank 50 is relatively lightweight, being preferably made from plastics material, although any suitable material can be used.

The above-described vertical tiered growing system may be adapted to hang from the roof rails by means of vertically extending arms onto which are mounted rollers, sliders or casters. The same ability to move the sections 1 relative to one another is achieved, without the need to provide track rails on the floor system, although in theory both systems can be provided.

It will be appreciated that the foregoing is merely descriptive of example embodiments of this invention and that modifications can readily be made to these embodiments without departing from the true scope of the invention as set out in the appended claims.

Claims (17)

1. A hydronic growing method, comprising: (i) depositing plant matter and a growth substrate within a plant tray which comprises an upper surface and one or more recesses for holding the plant matter; (ii) placing the plant tray on a stacking tray having a base and one or more upwardly projecting walls dimensioned so as to extend above the plant tray's upper surface when it is located on the stacking tray; (iii) repeating steps (i) and (ii) using second plant and stacking trays, and stacking the second stacking tray on top of the first stacking tray so that a gap is left between the upper surface of the first plant tray and the base of the second stacking tray; (iv) storing said stacked trays for an initial stage growing period in which plant growth can extend into the gap between stacked trays; and (v) unstacking the stacking trays and locating the first and second plant trays on one or more hydroponic flood table(s) for a second stage growing period.

2. A method according to claim 1, further comprising, subsequent to step (v) , the step (vi) of flooding the or each flood table(s) with a volume of nutrient-containing liquid so that its level is above that of the plant trays' upper surface to water the plant matter and growth substrate, and then draining the flood table, as part of a second stage growing period.

3. A method according to claim 2, further comprising the step (vii) of repeating step (vi) for subsequent flood and drain cycles over the second stage growing period.

4. A method according to claim 2 or claim 3, further comprising, subsequent to step (vi) or claim (vii), placing each plant tray on a respective stacking tray and stacking the stacking trays one on top of the other.

5. A method according to any preceding claim, wherein each plant tray comprises plural, non-draining recesses sunken into the upper surface.

6. A method according to any preceding claim, wherein the growth substrate is a layer of fibrous biodegradable material.

7. A method according to any preceding claim, wherein each stacking tray comprises a base of greater area than that of the plant tray.

8. A method according to claim 7, wherein the or each wall of the stacking tray projects upwardly by more than twice the depth of the plant tray.

9. A method according to claim 8, wherein the or each wall projects upwardly by more than three times the depth of the plant tray.

10. A method according to any of claims 7 to 9, wherein the or each wall of the stacking tray is arranged to completely surround an internal base area within which the plant tray sits flat in use.

11. A method according to any preceding claim, wherein the or each wall of the stacking tray has at or near its upper edge a surface shaped so as to receive the external base of another stacking tray in such a way as to limit lateral movement when stacked.

12. A method according to any preceding claim, wherein step (v) comprises locating the first and second plant trays on one or more hydroponic flood table(s) which are part of a vertical tiered flood and drain system.

13. A hydroponic growing method, comprising: (I) providing multiple plant trays, each plant tray comprising an upper surface and a plurality of sunken, nondraining recesses within which are received plant seeds or germinating plant seeds in or adjacent a substrate; (II) moistening the substrate; (III) placing each plant tray within a respective stacking tray which comprises a base larger than the plant tray and which has one or more surrounding walls which extend above the plant tray upper surface; (IV) stacking the stacking trays one on top of the other and storing them for a growth period in which the plants grow into the gap left between the plant tray and the stacking tray stacked above it; (V) subsequently unstacking the stacking trays, removing the plant trays and locating them on a flood table of a flood and drain system which periodically floods the flood table with nutrified liquid to a level just above that of the plant trays before draining said liquid, promoting further growth.

14. A stacking tray configured for use in the method according to any preceding claim, comprising a base having one or more upwardly projecting walls of greater height than a plant tray it is configured to hold.

15. A stacking tray according to claim 14, having a nondraining base.

16. A stacking tray according to claim 14 or claim 15, having at or near the upper periphery of the wall(s) a shaped part dimensioned and arranged to receive the base of another stacking tray to limit its lateral movement when stacked.

17. Apparatus configured for use in the method according to any preceding claim, comprising a plant tray having a plurality of recesses beneath an upper surface, and a stacking tray comprising a base of greater area than that of the plant tray with one or more upwardly projecting walls of greater height than the depth of the plant tray, so that there is a left a gap been the respective upper surfaces when the plant tray is located within the stacking tray.