WO2007056794A1

WO2007056794A1 - Hydroponic support medium of plastic pellets

Info

Publication number: WO2007056794A1
Application number: PCT/AU2006/001694
Authority: WO
Inventors: Robin Hosking
Original assignee: Australian Centre For Plant Functional Genomics Pty Ltd
Priority date: 2005-11-15
Filing date: 2006-11-15
Publication date: 2007-05-24

Abstract

Hydroponic support media (104) comprise plastics (eg polycarbonate) pellets (106) of specific gravity greater than water (e.g. 1.1 or 1.2), cylindrical (1-10 mm in length and 0.5-5.0 mm in diameter) and loosely arranged to define a network of fluid-permeable pore spaces between pellets (106). Biologically inactive, synthetic plastics, natural rubber latex, shellac, etc may be used for pellets (106). Preferably such materials should be sterilisable, etc to allow reuse and should not adhere to the roots of plants so that the roots will readily release for examination. Such media can be used to fill pots (100) with permeable bottoms (110) in hydroponic systems including flooding trays, reservoirs, pumps, timers etc.

Description

HYDROPONIC SUPPORT MEDIUM OF PLASTIC PELLETS

FIELD OF THE INVENTION

The present invention relates to the field of hydroponics. More particularly the present invention relates to hydroponic support media and plant growth vessels and hydroponic systems which incorporate such media.

BACKGROUND OF THE INVENTION

Hydroponic methods for growing plants generally do not utilise significant amounts of soil. As such, in hydroponic systems, a medium that supports the roots and/or anchors the plant is generally required. For example, hydroponic support media are generally pH neutral, provide support for plants, retain moisture, and allow space for good air exchange.

The type of media chosen for a given application will depend on the size and type of plants to be grown, and the type of hydroponic system being used. Examples of hydroponic support media include rockwool, perlite, vermiculite, expanded clay and coir fibre.

Rockwool is formed from rock, such as granite or limestone, which has been melted and spun into a fibrous mass. Rockwool absorbs moisture without holding nutrients. Even when completely saturated, rockwool still retains 20% air, which promotes root aeration. Small cubes are normally used for starting seeds and cuttings, 3" or 4" cubes may be used for small plants or intermediate growth, while slabs are used for larger plants. Rockwool can be used with continuous drip or flood and drain hydroponic systems. Perlite is mineral product that is subjected to intense heat, which causes it to expand and become absorbent. This material is light, has a neutral pH, has wicking action, and is porous. Perlite is used in a wide variety of hydroponic systems because of its ability to hold moisture and nutrients as well as air, and also because it is relatively easy to use. Perlite pellets can be used alone as growing medium, but generally do not provide enough anchorage for large plants. As such, perlite is often used to start seed and cuttings, which can be easily transplanted after rooting.

Vermiculite is another heat-expanded product that is used in a similar manner to perlite, with the two sometimes being mixed together in hydroponic media. Vermiculite has very high water retention and is often used as a soil conditioner. However, the very high water retention of this medium means that it is generally unsuitable as a growing medium on its own and, therefore, is generally used as a mixture with other hydroponic media.

Expanded clay media include clays that are super-fired to create a porous medium. Expanded clay media are generally heavy enough to provide secure support for plant root systems. Expanded clay media generally have relatively low water-retention, but provide a high level of aeration to the roots.

Coconut or coir fibre provides an organic alternative to using rockwool or other inorganic hydroponic media. Coconut fibre can be used on its own, or can be added into mixtures to increase water-holding capacity. Coconut fibre generally has higher porosity than rockwool (which facilitates greater aeration of the medium) and is pH neutral. Coconut fibre is generally available as compressed bricks that, when soaked in water, expand to about 6 times their compressed size.

However, existing hydroponic media suffer from a number of disadvantages. For example, known hydroponic support media generally tend to adhere to plant roots to some extent. This presents a problem when it is desirable to be able to remove the plants from the media in a relatively undamaged state, for example, when root morphology of the plant is of interest to the grower. Furthermore, the adherence of the support media to the plant roots can also make separation of the roots from the medium difficult and thus contribute to medium contamination of any later analysis of the roots.

A further problem with known hydroponic media relates to their relative non- reusability. In many cases the media cannot be effectively cleaned and/or sterilised between uses, such that later plants may be grown in the same medium. Alternatively, if the medium may be sufficiently cleaned and/or sterilised, this cleaning or sterilising process may render the medium unsuitable for later plant growth. For example, the cleaning or sterilising process may lead to degradation of the medium structure and/or the retention of the cleaning or sterilising agent in the medium, which may leach out and lead to deleterious effects on later plant growth.

The present invention relates to a hydroponic support medium which, in at least some embodiments, overcomes at least some of the limitations of existing hydroponic support media.

Reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that this prior art forms part of the common general knowledge in any country.

SUMMARY OF THE INVENTION

The present invention is predicated, in part, on the discovery that plastic pellets, which are arranged to define a network of fluid-permeable pore spaces between the pellets, are suitable as a hydroponic support medium.

Accordingly, in a first aspect, the present invention provides a hydroponic -A-

support medium, the medium comprising a plurality of plastic pellets, wherein the plastic pellets are arranged to define a network of fluid-permeable pore spaces between the pellets.

One particular benefit of the hydroponic support medium of the present invention is that the plastic pellets exhibit minimal or substantially no adherence to plant roots. Therefore, the roots of a plant grown in the medium may be readily released from the medium. This enables a plant to be removed from the medium with minimal damage to the root system. Furthermore, once removed from the medium, little to none of the medium remains adhered to the roots.

The pellets used in the hydroponic support medium may further comprise one or more of the following characteristics: reusability, hydrophilic, substantially biologically inert, and a specific gravity greater than a nutrient solution which is used in conjunction with the hydroponic support medium.

In a second aspect, the present invention further provides a plant growth vessel, the vessel containing the hydroponic support medium of the first aspect of the invention.

In a third aspect, the present invention provides a hydroponic system comprising: at least one plant growth vessel of the second aspect of the invention; a nutrient solution reservoir containing a nutrient solution; and means to transfer nutrient solution from the nutrient solution reservoir to the at least one plant growth vessel;

The present invention also provides methods for growing plants, wherein the methods utilise the hydroponic support medium, vessel or hydroponic system hereinbefore described.

Accordingly, in a fourth aspect, the present invention provides a method for growing a plant, the method comprising planting a plant, plantlet, cutting or seed into the hydroponic support medium of the first aspect of the invention and administering a nutrient solution to said plant and allowing the plant to grow.

In a fifth aspect, the present invention provides a method for growing a plant, the method comprising planting a plant, plantlet, cutting or seed into the hydroponic support medium in a plant growth vessel of the second aspect of the invention and administering a nutrient solution to said plant and allowing the plant to grow.

In a sixth aspect, the present invention provides a method for growing a plant, the method comprising planting a plant, plantlet, cutting or seed into the hydroponic support medium in a plant growth vessel which is part of the hydroponic system of the third aspect of the invention and administering a nutrient solution to said plant and allowing the plant to grow.

In a seventh aspect, the present invention provides the use of a plurality of plastic pellets, wherein the plastic pellets are arranged to define a network of fluid-permeable pore spaces between the pellets, as a hydroponic support medium.

In an eighth aspect, the present invention provides a combination product for growing a plant, the product comprising a hydroponic support medium comprising a plurality of plastic pellets arranged to define a network of fluid- permeable pore spaces between the pellets; together with a nutrient solution.

Throughout this specification, unless the context requires otherwise, the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element or integer or group of elements or integers but not the exclusion of any other element or integer or group of elements or integers. BRIEF DESCRIPTION OF THE FIGURES

Having briefly described the general concepts involved with the present invention, exemplary embodiments of the present invention will now be described with reference to the following figures:

Figure 1 shows a plant growth vessel according to a specific embodiment of the invention. Panel A shows a front elevation of a plant growth vessel of one embodiment the invention; Panel B shows a cross-sectional view across line A- A in Panel A.

Figure 2 shows a front elevation view of a hydroponic system according to one specific embodiment of the present invention.

Figure 3 shows a front elevation view of a frame or trolley mounted hydroponic system according to a further embodiment of the present invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

It is to be understood that the following description is for the purpose of describing particular embodiments only, and is not intended to be limiting with respect to the above description.

The present invention is predicated, in part, on the discovery that plastic pellets which are arranged to define a network of fluid-permeable pore spaces between the pellets are suitable as a hydroponic support medium for growing plants. The hydroponic support medium of the present invention has been identified to provide, among other things, adequate mechanical support for plant roots, suitable rates of inundation and drainage of a nutrient solution, and suitable levels of root aeration. Accordingly, in a first aspect, the present invention provides a hydroponic support medium, the medium comprising a plurality of plastic pellets, wherein the plastic pellets are arranged to define a network of fluid-permeable pore spaces between the pellets.

As set out above, the plastic pellets of the hydroponic support medium exhibit minimal or substantially no adherence to plant roots. Therefore, the roots of a plant grown in the medium may be readily released from the medium. This enables a plant to be removed from the medium with minimal damage to the root system. Furthermore, once removed from the medium, little to none of the medium remains adhered to the roots.

Therefore, the use of the medium of the present invention, for example, facilitates more accurate analysis of plants grown in the hydroponic support medium. Specifically, as plants may be removed from the medium in a relatively undamaged state, later analysis of the plant and/or plant roots is likely to be more accurate, and damage-related artefacts would be reduced or eliminated, when compared to plants grown in hydroponic support media that adheres to roots. Furthermore, because little to no medium remains on the roots, the medium facilitates more accurate analysis of the roots, as medium contamination of roots is minimised.

As referred to herein, the term "plastic" should be understood to encompass a range of synthetic or semisynthetic polymerization products. The vast majority of plastics are composed of polymers of carbon alone or with oxygen, nitrogen, chlorine or sulfur in the backbone, although some plastics also comprise silicon.

As is known in the art, plastics with different properties may be produced by incorporating different molecular groups into the polymer backbone and/or by combining polymers of different characteristics.

As set out above, plastics commonly comprise organic condensation or addition polymers and may also contain other substances. However, the term "plastic" may also encompass natural polymers, such as chewing gum, natural rubber latex or shellac.

Plastics can be classified in many ways but are commonly classified by their polymer backbone (polycarbonate, polyvinyl chloride, polyethylene, acrylic, silicone, urethane, etc.). A range of exemplary "plastics" include, for example: polyethylene (PE), polypropylene (PP), polystyrene (PS), polyethylene terephthalate (PETE), Polyamide (PA) (Nylon), polyester, polyvinyl chloride (PVC), polycarbonate, acrylonithle butadiene styrene (ABS), polyvinylidene chloride (PVDC), Teflon, Polyurethane and Bakelite.

In some embodiments of the invention, the plastic pellets of the hydroponic support medium comprise a plastic which may be washed, sterilised or otherwise treated after use such that the hydroponic support medium may be reused.

In further embodiments, the plastic pellets of the hydroponic support medium may be rinsed in water, washed in a detergent solution, washed in a sterilising agent such as sodium hypochlorite or other bleaches, sterilised in an atmosphere of ethylene oxide gas, irradiated with sterilising radiation such as gamma or UV radiation, or the like, using methods known in the art. In some embodiments, when plastic pellets used have a suitable melting temperature, the medium may also be heat and/or steam sterilised, for example in an autoclave.

In a further embodiment, the plastic pellets of the hydroponic support medium are substantially non-porous. The substantial non-porosity of the plastic pellets means that the plastic pellets do not retain substantial amounts of a cleaning or sterilising agent within the pellets after rinsing of the pellets. As such, the pellets are unlikely to leach out substantial amounts of the cleaning or sterilising agent after the pellets have been cleaned or sterilised with a cleaning or sterilising agent.

In some embodiments, the hydroponic support medium of the present invention may be reused at least 5 times, at least 10 times or at least 20 times, while not exhibiting any substantial degradation in its ability to function as a hydroponic support medium.

In a further embodiment, the plastic pellets of the hydroponic support medium are hydrophilic. As referred to herein the term "hydrophilic" should be understood to mean that the plastic pellets are wettable by water and not water repellent (ie. not hydrophobic). It has been recognised that the wettable nature of hydrophilic plastic pellets results in the pellets being able to hold an aqueous solution on their surface, which is advantageous in that this surface moisture slows or prevents the desiccation of plant roots that are in contact with the pellets. In alternate embodiments, however, the plastic may be substantially non-hydrophilic or may be hydrophobic.

In another embodiment, the plastic pellets of the hydroponic support medium are substantially biologically inert.

As referred to herein, the term "substantially biologically inert" should be understood to mean that the plastic pellets, under plant growth conditions, do not leach out any chemical in a concentration sufficient to have a significant adverse effect on the growth of a plant grown in the medium.

In yet another embodiment, the plastic pellets of the hydroponic support medium have a higher specific gravity than a nutrient solution which is used in conjunction with hydroponic support media. Therefore, the plastic pellets of the hydroponic support medium generally have a sufficiently high specific gravity such that they will sink in a nutrient solution.

Specific gravity is the ratio of the density of a material to the density of water at 4⁰C. The density of water at 4°C is approximately 1 gram per cubic centimetre. Accordingly, materials which are less dense than water at 4°C (ie. have a specific gravity less than 1.0) will float.

Typically, hydroponic nutrient solutions are water based and, therefore, have specific gravities similar to that of water, ie. about 1.0.

Therefore, in some specific embodiments, the plastic pellets of the hydroponic support medium have a specific gravity of greater than 1.0, a specific gravity of at least 1.1 or a specific gravity of at least 1.2.

In yet another embodiment, the plastic pellets of the hydroponic support medium exhibit minimal or no translucency. It has been also recognised that the use of plastic pellets that exhibit minimal, or substantially no translucency, means that light does not substantially penetrate into the medium or penetrates only a short distance into the medium. The low light penetration into the medium is desirable in that the growth of light-dependent contaminant organisms, such as algae, is prevented or inhibited in the hydroponic support medium. In one particular embodiment, the plastic pellets are of a dark colour, eg. black, which has low or no translucency.

As set out above, the plastic pellets of the hydroponic support medium may comprise any suitable plastic. However, in one specific embodiment, the plastic pellets of the hydroponic support medium are formed from polycarbonate.

Polycarbonate is a hydrophilic plastic with a specific gravity of in the range of about 1.2 to about 1.6, and which exhibits very little or no adherence to plant roots. Furthermore, polycarbonate has a melting point of approximately 280⁰C, which enables the plastic to be sterilised in an autoclave under standard conditions.

In another specific embodiment, the hydroponic support medium may comprise ABS plastic pellets.

As will be appreciated, the plastic pellets of the hydroponic support medium may also comprise a mixture of plastics within each pellet or may comprise a mixture of plastic pellets formed from different plastics.

As set out above, the hydroponic support medium of the present invention contemplates plastic pellets arranged to define a network of pore spaces between the plastic pellets. The network or pore spaces between the pellets facilitates the inundation and drainage of the support medium with a nutrient solution, and further allows aeration of the roots when a nutrient solution is drained from the medium.

The plastic pellets used in accordance with the present invention may be of any suitable size, which may in part be determined by the type and size of plant that is to be grown in the medium.

Suitable plastic pellets include, for example, those wherein each of the length, width and height of the pellet are less than about 30 mm, less than about 20 mm or less than about 10 mm.

In one specific embodiment, it has been identified that substantially cylindrical shaped pellets having a length of about 2 mm to about 4 mm and a diameter of about 1 mm, define a network of pore spaces between pellets which provides particularly suitable inundation and drainage rates of a nutrient solution applied to the hydroponic support medium.

However, as would be recognised by one of skill in the art, variation in the shape and/or specific dimensions of the pellets may be accommodated without substantially affecting the particularly suitable inundation and drainage rates achieved with pellets having the particular sizes noted above. Accordingly, in further specific embodiments, the plastic pellets may be about 1 -10 mm in length and have a diameter of about 0.5-5 mm.

The present invention also contemplates hydroponic support media which comprise two or more different types and/or different sizes of plastic pellets. For example, mixtures of different type or size plastic pellets may be used to modulate the characteristics of the hydroponic support medium, for example, characteristics such as the overall hydrophilicity, the aeration rate, the drainage rate and the specific gravity of the medium may be modulated by using a mixture of plastic pellets with different characteristics or sizes in the hydroponic support medium. Furthermore, a hydroponic support medium with different characteristics over several strata may be produced by forming layers of different sized plastic pellets in a hydroponic support medium.

In one embodiment, at least a portion of said vessel is fluid-permeable. As referred to herein, a "fluid-permeable" portion of the vessel includes, for example, any portion of the vessel through which a liquid, such as a hydroponic nutrient solution may pass into or out of the vessel.

In another embodiment, the vessel comprises a fluid-permeable portion that is substantially impermeable to the hydroponic support medium in the vessel. As such, the fluid-permeable portion of the vessel may comprise, for example, a woven material or mesh that comprises pore spaces that are smaller than the plastic pellets of the hydroponic support medium. Exemplary woven materials or meshes include weed matting, no see urn mesh, fluid-permeable textile fabrics, metal meshes and the like.

In a yet another embodiment, the fluid-permeable portion of the vessel is located in the vessel below the surface of the hydroponic support medium in the vessel. In this way, a nutrient solution applied to the vessel may drain out of the vessel through the fluid-permeable portion. Furthermore, this fluid-permeable portion may also be used to effect flooding of the growth medium in the vessel, for example when the vessel is used in a flood and ebb hydroponic system (described later). In a further embodiment, at least the base of the plant growth vessel is fluid-permeable.

As will be appreciated, substantially the entire vessel may be fluid-permeable, for example, the vessel may be substantially completely constructed from a fluid-permeable woven material or mesh.

In another embodiment, in addition to the fluid-permeable portion, the vessel of the present invention may further comprise an aperture to allow outgrowth of a plant from the vessel.

However, in an alternate embodiment, the vessel may be enclosed above the surface of the growth medium and a plant may be grown in the headspace of the container between the surface of the growth medium and the top of the vessel.

In one specific embodiment, and as shown with reference to Figure 1 , the present invention provides a plant growth vessel 100 comprising a tubular body 102 containing the hydroponic support medium of the present invention 104, comprising plastic pellets 106 arranged to define a network of pore spaces 108 between the plastic pellets 106; wherein the base of the tubular body 102 is closed with weed-matting 1 10, which is fluid-permeable but impermeable to the plastic pellets 106, and comprises an aperture 1 12, at the opposite end, to allow outgrowth of a plant 1 14 from the vessel 100.

In one embodiment, at least one plant growth vessel in the system comprises a fluid-permeable portion wherein nutrient solution transferred to the vessel may drain out of the vessel via the fluid-permeable portion of the vessel.

In a further embodiment, the system further comprises means for returning nutrient solution that drains out of the one or more plant growth vessels to the nutrient solution reservoir.

In a yet further embodiment, the hydroponic system of the present invention utilises an ebb and flood system (also referred to as a 'flood and ebb' system or an 'ebb and flow' system) for transferring the nutrient solution to the at least one plant growth vessel and subsequently effecting drainage of the nutrient solution from the plant growth vessel. The characteristic features of an ebb and flow system would be well known to one of skill in the art.

Known ebb and flood systems generally utilise a flooding tray and a reservoir of nutrient solution. The flooding tray is either filled with a support medium and planted directly, or vessels filled with support medium stand in the tray. At regular intervals, a timer causes a pump to fill the flooding tray with nutrient, thus inundating the medium in the tray, or the medium in the pots in the tray, with nutrient solution. After a period, the pump is switched off and the nutrient drains out of the flooding tray back down into the nutrient solution reservoir. This cycling of flood and ebb periods keeps the support medium regularly flushed with nutrient and air.

Accordingly, in one specific embodiment, the hydroponic system further comprises a flooding tray including one or more plant growth vessels; wherein the nutrient solution is transferred to the one or more plant growth vessels by filling the flooding tray with nutrient solution such that the nutrient solution enters the plant growth vessel(s) via a fluid-permeable portion of the plant growth vessel(s); and draining of nutrient solution from the plant growth vessel(s) is effected by draining nutrient solution from the flooding tray, such that nutrient solution drains out of the plant growth vessel(s) via the fluid permeable portion thereof.

In further embodiments, the plant growth vessels are held within the flooding tray such that the bases of the plant growth vessels are spaced apart from the base of the flooding tray. Spacing these surfaces apart reduces the surface tension of nutrient solution between the base of the vessel and the base of the flooding tray and thus improves the rate of infiltration and drainage of nutrient solution into or out of the growth vessels.

The present invention contemplates any method for holding the bases of the plant growth vessels spaced apart from the base of the flooding tray. For example, the plant growth vessels may sit on a fluid-permeable shelf above the base of the flooding tray or, alternatively, a plant growth vessel may be suspended in the flooding tray such that there is a space between the base of the plant growth vessel and the base of the flooding tray.

In one specific embodiment, the bases of the plant growth vessels are spaced apart from the base of the flooding tray by the provision of a shelf comprising a fluid-permeable mesh spaced above the base of the flooding tray and the placement of the plant growth vessels on this shelf.

As set out above, the hydroponic system of the present invention includes means to transfer nutrient solution to a plant growth vessel and/or flooding tray and, optionally, means to return nutrient solution that drains out of the plant growth vessels, and/or flooding tray, to the nutrient solution reservoir.

The means to transfer nutrient solution from the nutrient solution reservoir and/or means to return nutrient solution to the nutrient solution reservoir may include any liquid transfer means known in the art. This may include, for example, reticulated pipes, sprayers, drippers, and the like. Furthermore, the nutrient solution may be moved through the means to transfer nutrient solution and/or means to return nutrient solution to the nutrient solution reservoir via gravity feed, one or more pumps or a combination thereof.

In some embodiments, at least the means to transfer nutrient solution from the nutrient solution reservoir to the one or more plant growth vessels comprises a pump.

Pumps including metal parts in contact with the nutrient solution may release metal ions (eg. Fe ions) into the nutrient solution and thus contaminate it. Accordingly, in one embodiment, substantially all of the parts of the pump in contact with the nutrient solution are non-metallic. Suitable pumps include, for example, those with ceramic spindles. Suitable ceramic-spindle pumps are available commercially from manufacturers such as EHEIM®.

In another embodiment, a timer controls the operation of the pump. Any timer which can effect switching of the pump from active to inactive may be used. As such, the term "timer", as used herein, incorporates any electrical timer switches known in the art, many of which are available commercially.

In a further embodiment, the timer is an "asymmetrical timer". As referred to herein an "asymmetrical timer" refers to a timer that has separately programmable on and off periods (also known as pulse and pause periods). For example, the asymmetrical timer used in accordance with some embodiments of the invention has independently programmable on and off periods which may be between 0.1 seconds and 100 hours. The variable on and off periods accommodate, among other things, different size nutrient solution and flooding trays and/or different pumping and/or drainage rates from one to the other. The pump and/or asymmetrical timer may be powered by any suitable power source including, for example, mains power, batteries, one or more photovoltaic cells and the like.

In one specific embodiment, the present invention provides a hydroponic system as shown in Figure 2. The hydroponic system 200 comprises a flooding tray 202 including a plurality of plant growth vessels 100, as previously described, sitting atop a nutrient solution reservoir 204. In this embodiment, the plant growth vessels sit atop a shelf made of oyster mesh (not shown), which is disposed inside and above the base of the flooding tray. In this embodiment, the nutrient solution reservoir 204 and the flooding tray 202 comprise stacked plastic crates.

The nutrient solution reservoir is connected to the flooding tray via a supply line 206. Nutrient solution (not shown) is pumped from the nutrient solution reservoir 204, through the supply line 206 to the flooding tray 202, when pump 208 is active. A timer switch (not shown) between the pump 208 and the power supply for the pump controls the activity of the pump 208. Pumping of nutrient solution from the nutrient solution reservoir 204 to the flooding tray 202, raises the level of liquid in the flooding tray 202. Raising the level of nutrient solution in the flooding tray 202 causes the plant growth vessels 100 to be flooded with nutrient solution to a depth equal to the level of nutrient solution in the flooding tray 202. The nutrient solution enters the plant growth vessels 100 through fluid- permeable portions in the vessels (eg. see 1 10 in Figure 1 ).

In an alternate embodiment, the flooding tray 202 may be directly filled with hydroponic support medium 104, effectively making the flooding tray 202 one large plant growth vessel, as defined herein.

If the level of liquid in the flooding tray reaches the level of the overflow outlet 210, excess nutrient solution flows through the overflow outlet 210, through the overflow pipe 212, before returning to the nutrient solution reservoir 204, through the overflow inlet 214.

When pump 208 is inactive, if nutrient solution is present in the flooding tray 202, the nutrient solution in the flooding tray 202 flows back down through the supply line 206 from the flooding tray 202 to the nutrient solution reservoir 204. This draining of the nutrient solution reservoir 202 effects a lowering in the level of nutrient solution in the plant growth vessels 100, which causes the nutrient solution to ebb or drain out of the plant growth vessels 100 through the fluid- permeable portions (eg. see 1 10 in Figure 1 ).

Accordingly, as can be seen, a controlled switching of the pump 208 from active to inactive effects cycles of nutrient solution flood and ebb in the flooding tray 202, which in turn effects flood and ebb of the nutrient solution in the plant growth vessels 100.

The combined weight of the plants, the support medium and the nutrient solution are important considerations for hydroponic systems. Therefore, for larger systems, particularly those incorporating multiple plant growth vessels or multiple ebb and flow flooding trays, it may be necessary to mount the system on a frame which substantially supports the weight of the system.

Accordingly, in a further embodiment, the hydroponic system of the present invention may be mounted on a frame.

Mounting of the hydroponic system on a frame also enables larger hydroponic systems to be moved as a single unit, thereby greatly easing the transport of such systems. In this regard the frame may also comprise wheels or rollers, thus forming a trolley, such that the hydroponic system may be easily moved.

One specific embodiment of a frame or trolley mounted hydroponic system is shown in Figure 3. In this embodiment, the trolley mounted system 300 comprises a relatively large nutrient solution reservoir 302 mounted on the lower tier of two-tiered trolley 304. On the upper tier of the trolley 306 are mounted two flooding trays 202, which may either contain one or more plant growth vessels 100 or may be directly filled with the hydroponic support medium 104. The trolley also comprises wheels 308 to facilitate easy movement of the trolley. In this embodiment, an asymmetrical timer switch (not shown) controls the activity of a pump (not shown) which transfers nutrient solution from the relatively large nutrient solution reservoir 302 to the flooding trays 202.

In further aspects, the present invention also provides methods for growing plants, wherein the methods utilise any of the hydroponic support medium, vessel or hydroponic system hereinbefore described.

In a sixth aspect, the present invention provides a method for growing a plant, the method comprising planting a plant, plantlet, cutting or seed into the hydroponic support medium in plant growth vessel which is part of the hydroponic system of the third aspect of the invention and administering a nutrient solution to said plant and allowing the plant to grow.

As described herein, in some embodiments, the present invention contemplates the use of a hydroponic nutrient solution in combination with the hydroponic support medium. In this regard, any suitable nutrient solution known in the art may be used. The choice of nutrient solution may depend on factors such as the type of plant to be grown, environmental conditions and the anticipated time between changes of the nutrient solution.

Examples of nutrient solutions that may be used in conjunction with the hydroponic support media of the present invention include the Sachs and Stδckhardt macronutrient solution (1 g KNO₃, 0.5g CaSO₄, 0.4g MgSO₄ x 7 H₂O, 0.5g CaHPO₄ and a trace of FeCI₃ per 1000 ml water), the Knop macronutrient solution (1g Ca(NO₃)₂, 0.25g MgSO₄ x 7 H₂O, 0.25g KH₂PO₄, 0.25g KNO₃ and a trace of FeSO₄ per 1000 ml water) and the like.

Macronutrient solutions such as those above may also be supplemented with micronutrients, for example, Hoaglands micronutrient solution (0.5g LiCI, 1g CuSO₄ x H₂O, 1g ZnSO₄, 1 1 g H₃BO₃, 1g AI₂(SO₄)₃, 0.5g SnCI₂ x 2 H₂O, 7g MnCI₂ x 4 H₂O, 1 g NiSO₄ x 6 H₂O, 1 g Co(NO₃)₂ x 6 H₂O, 0.5g Kl, 1g TiO₂, 0.5g KBr in 18 I water; added at 1 ml per litre of macronutrient solution).

In one embodiment, the methods of the present invention may be used to hydroponically grow cereal crop plants, for example, wheat, barley, oats, rice, maize and the like. In this embodiment, the nutrient solution presented in Table 1 is particularly suitable.

TABLE 1 - Cereal Growth Solution

IJBIBH.1I Concentration (in water

Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is to be understood that the invention includes all such variations and modifications. The invention also includes all of the steps, features, compositions and compounds referred to, or indicated in this specification, individually or collectively, and any and all combinations of any two or more of the steps or features.

Also, it must be noted that, as used herein, the singular forms "a", "an" and "the" include plural aspects unless the context already dictates otherwise. For example "a plant growth vessel" may be a single vessel or may include a plurality of such vessels.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1 . A hydroponic support medium, the medium comprising a plurality of plastic pellets, wherein the plastic pellets are arranged to define a network of fluid-permeable pore spaces between the pellets.

2. The hydroponic support medium of claim 1 wherein the medium is reusable.

3. The hydroponic support medium of claim 1 or 2 wherein the pellets are hydrophilic.

4. The hydroponic support medium of any one of claims 1 to 3 wherein the pellets are substantially biologically inert.

5. The hydroponic support medium of any one of claims 1 to 4 wherein the plastic pellets have specific gravity of greater than 1 .0.

6. The hydroponic support medium of any one of claims 1 to 5 wherein each of the length, width and height of each pellet is less than about 30 mm.

7. The hydroponic support medium of claim 6 wherein the pellets are of substantially cylindrical shape having a length of about 1 -10 mm and a diameter of about 0.5-5 mm.

8. The hydroponic support medium of claim 7 wherein the pellets are of substantially cylindrical shape having a length of about 2-4 mm and a diameter of about 1 mm.

9. The hydroponic support medium of any one of claims 1 to 8 wherein the plastic pellets are substantially non-translucent.

10. The hydroponic support medium of any one of claims 1 to 9 wherein the plastic pellets are polycarbonate pellets.

1 1 . A plant growth vessel, the vessel containing the hydroponic support medium of any one of claims 1 to 10.

12. The plant growth vessel of claim 1 1 wherein at least a portion of the plant growth vessel is fluid-permeable.

13. The plant growth vessel of claim 12 wherein the fluid-permeable portion of the vessel is below the surface of the support medium in the vessel.

14. The plant growth vessel of any one of claims 1 1 to 13 wherein the plant growth vessel comprises an aperture to allow outgrowth of a plant from the vessel.

15. A plant growth vessel comprising a tubular body containing the hydroponic support medium of any one of claims 1 to 10; wherein the tubular body is closed at one end with a membrane that is fluid-permeable but impermeable to the growth medium, and comprises at the opposite end, an aperture to allow outgrowth of a plant from the vessel.

16. A hydroponic system comprising: at least one plant growth vessel of any one of claims 1 1 to 15; a nutrient solution reservoir containing a nutrient solution; and means to transfer nutrient solution from the nutrient solution reservoir to the at least one plant growth vessel;

17. The hydroponic system of claim 16 wherein at least one plant growth vessel comprises a fluid-permeable portion and nutrient solution transferred to the vessel drains out of the vessel via the fluid-permeable portion of the vessel.

18. The hydroponic system of claim 17, wherein the system further comprises means for returning nutrient solution that drains out of the one or more plant growth vessels to the nutrient solution reservoir.

19. The hydroponic system of claim 17 or 18 further comprising a flooding tray including one or more plant growth vessels of any one of claims 12 to 15; wherein the nutrient solution is transferred to the one or more plant growth vessels by filling the flooding tray with nutrient solution such that the nutrient solution enters the plant growth vessel(s) via the fluid-permeable portion of the plant growth vessel(s); and draining of nutrient solution from the plant growth vessel(s) is effected by draining nutrient solution from the flooding tray, such that nutrient solution drains out of the plant growth vessel(s) via the fluid permeable portion thereof.

20. The hydroponic system of claim 19 wherein the plant growth vessels are located such that the bases of the plant growth vessels are spaced apart from the base of the flooding tray.

21 . The hydroponic system of any one of claims 16 to 20 wherein the means to transfer nutrient solution comprises a pump.

22. The hydroponic system of claim 21 wherein the substantially all of the parts of the pump in contact with the nutrient solution are non-metallic.

23. The hydroponic system of any one of claim 21 or 22 wherein a timer controls the operation of the pump.

24. The hydroponic system of claim 23 wherein the timer is an asymmetrical timer.

25. The hydroponic system of any one of claims 16 to 24 wherein the hydroponic system is mounted on a frame.

26. A method for growing a plant, the method comprising planting a plant, plantlet, cutting or seed into the hydroponic support medium of any one of claims 1 to 10 and administering a nutrient solution to said plant and allowing the plant to grow.

27. A method for growing a plant, the method comprising planting a plant, plantlet, cutting or seed into the hydroponic support medium in a plant growth vessel of any one of claims 1 1 to 15 and administering a nutrient solution to said plant and allowing the plant to grow.

28. A method for growing a plant, the method comprising planting a plant, plantlet, cutting or seed into the hydroponic support medium in a plant growth vessel which is part of the hydroponic system of any one of claims 16 to 25 and administering a nutrient solution to said plant and allowing the plant to grow.

29. Use of a plurality of plastic pellets as a hydroponic support medium, wherein the plastic pellets are arranged to define a network of fluid-permeable pore spaces between the pellets.

30. A combination product for growing a plant, the product comprising a hydroponic support medium comprising a plurality of plastic pellets arranged to define a network of fluid-permeable pore spaces between the pellets; together with a nutrient solution.

31 . The hydroponic support medium according to any one of claims 1 to 10 substantially as hereinbefore described with reference to any of the figures.

32. The plant growth vessel according to any one of claims 1 1 to 15 substantially as hereinbefore described with reference to any of the figures.

33. The hydroponic system according to any one of claims 16 to 25 substantially as hereinbefore described with reference to any of the figures.