Background to the Invention The applicant has conducted research into the relationship between root medium volume and plant growth rate and fruitfulness. The research with a wide range of plants including cucumber, cabbage, parsley, ornamental plants such as cypress, eucalypt, birch, bamboo, camelias and fruiting plants such as apple, grape, pear and tomato shows that the growth rate over a range of root volumes from 100cc. to 100 litres is positively correlated with the root media volume. This relationship occurs with soil and hydroponically grown plants. In fruit plants the harvest index (dry or fresh weight of fruit relative to total plant weight or leaf area) which is a measure of biological efficiency, is negatively correlated with the root media volume.

Similarly plant weight and fruit weight per unit of water or nitrogen taken up by the plant decreases as the root media volume increases. The total weight, leaf area, mean leaf area and the mean root diameter of all the roots in the root system increases in a logarithmic manner as the volume of the media increases. This suggests the mean root diameter controls the rate of water and nitrogen uptake from the soil to the leaf.

It would be useful to be able to control plant root size and spread and hence vegetative growth rate and fruit harvest index in fruiting crops. It would also be useful to improve radial growth in plants, prevent root strangulation and improve drainage relative to conventional pots and containers used in plant nurseries.

Object of the Invention It is an object of the invention to go at least some way in providing a method of achieving the above concept or to at least provide the public with a useful choice.

Summary of the Invention According to the invention there is provided a method of controlling plant growth and fruitfulness by restricting the growth of the root system in specific volumes of rooting medium in which the root system is enclosed by a porous barrier in the form of a bag or soil liner with rigid holes which provide adequate drainage and only allow up to 0.2mm in diameter roots to pass through them.

Extrapolation of the applicant's research data shows that under the suction pressures that can be generated by leaves that the water uptake through a root is zero when the root diameter is 0.2mm and nitrogen uptake is zero at a root diameter of 0.1mm.

The minimum diameter that a root can be is species dependent. For a wide range of tree, vines and shrubs tested this is greater than 0.2mm. For many vegetables it is less than 0.2mm. In bags or liners with holes 0.2mm in diameter roots of lettuce and cabbage will grow through the holes into the surrounding media. For other plants

0.2mm holes will prevent roots escaping from the bag or liner. However, for all plants tested 0.2mm root diameter appears to be the limit below which such roots cease to contribute to water uptake and 0.1 mm for nitrogen uptake.

For plants which have a minimum root diameter greater than 0.2mm the growth rate in a given bag size is the same whether buried or above ground. For those with a minimum root diameter 0.2mm or less the plants in bags buried in the ground have a slightly faster growth rate than when grown above ground. With these plants roots between 0.2mm and 0.1mm in diameter can maintain some nitrogen uptake but at a much reduced rate. These escaped roots however do not appear to be involved in water uptake and the volume of the root media is still the major factor which determines plant growth rate.

The density of the 0.2mm holes in the material used to confine the roots does not appear to affect the growth rate of the plant unless it is less than four holes per square centimetre. Hole density is only of importance as it affects drainage. The higher the hole density the faster the container will drain.

The applicant's research has shown that a hole density of four per square centimetre drains in fifty to sixty minutes depending on the container depth per volume. Bags with sixteen holes per square centimetre drain in fifteen to sixteen minutes. The slower the drainage at four holes per square centimetre does not reduce the growth rate compared to sixteen holes per square centimetre. The slower drainage results in

a more thorough wetting of the soil volume than a faster draining bag. Below four holes per square centimetre drainage is too slow and causes water-logging damage.

Although hole densities greater than two per square centimetre provide adequate drainage, four holes per square centimetre is the preferred density because it minimizes manufacturing costs and maintains the physical strength of the bags better than much higher densities. At four 0.2mm holes per square centimetre the total area taken up with holes is only 0.126 percent of the area of the material.

When grown above ground the size and density of the holes are less important other than that they affect drainage rate. The roots are confined within the bag as air pruning prevents roots penetrating the holes in the bag. At four 0.2mm holes per square centimetre the bags drain satisfactorily and give a good distribution of water throughout the root media. Very large holes and high density can lead to fast drainage and channeling of water applied down the inside surface of the bag along the line of least resistance causing uneven wetting.

The bags or soil liners can be made of any flexible or rigid material such as metals, ceramics, plastics or woven, knitted or laminated fabric provided the material has one or more and preferably all of the following properties: (a) light and heat stable for above ground use; (b) resistant to degradation when wet or buried in the soil ; (c) has high tensile strength and resistance to stretching;

(d) when manufactured the diameter of the pores or holes in the material can be accurately controlled and do not stretch against the secondary thickening of the roots which might pass through them. This has been found to be a problem with knitted, woven or bonded fabrics; (e) the material is capable of being glued or welded so that any seams which are necessary in manufacture do not provide points of weakness in the bags or liners made from it; (f) the material is capable of being shaped into any bag or soil liner volume required; (g) the material is price competitive with any material or container now used for growing plants; (h) has properties that allow the holes to be manufactured rapidly and cheaply.

PVC perforated by hot points has the advantage of giving a precise, clean cut hole strengthened at its circumference with melted plastic. Needle puncturing creates fractures in the plastic and potentially weakens the rigidity of the holes; and (i) the thickness of the conventional robust PVC plastic used at present in the nursery industry for planter bags has proved to be a highly suitable material both on a cost and strength basis. However, the choice of this material does not exclude other materials which meet the specifications as described above. The invention covers such other materials that are or could become available which have the same purpose or function.

Description of the Drawings The invention will now be described, by the way of example only and with reference to the attached drawings in which: Figure 1 shows two bonsai plants in bags above ground in which the bag volume ratio between the plants is 10: 1 whilst the plant weight is 2: 1.

Figure 2 shows two bonsai plants buried in soil showing the root system extending through the bags. The bag volume ratio and plant weight ratio is the same as in Figure 1.

Figure 3 shows a plant in a soil liner.

Figure 4 shows the restriction of a root by a bag or liner wall.

Detailed Description of the Preferred Embodiments The bags shown in Figures 1 and 2 are manufactured from a sheet PVC material and contain four holes per square centimetre and for clarity only some of the holes are shown.

In Figure 3 is shown a soil liner constructed from a continuous sheet or strip of a PVC material again with about four holes per square centimetre. In this case the sheet of material is formed into a trough which can be laid in a trough formed in the ground or

in an appropriate frame not shown which forms a trough when the growing media is placed in the material.

In Figure 4 a root 2 is shown growing from right to left. The pore or hole through a bag or liner wall 4 is shown at 6. As the root diameter increases, it reaches and then expands either side of the wall 4. At a certain point the wall 4 restricts the root penetration 8. Eventually the root 2 is severed 10 and the end of the root 12 detaches. Hence the root 2 is restricted in its growth by the size of the pore 6 as shown at 14.

Roots pass through the holes in the bag wall when they are equal to or smaller than the diameter of these holes. The diameter of the root is restricted within the bag holes even through it may expand on either side of the bag. When the bags are above ground roots do not pass out of the bag due to dehydration of roots by air.

This referred to as air pruning. Even when bags or liners are buried the restriction within the wall of the bag may become so severe that the root external to the bag eventually dies due to the restricted phloem being unable to supply enough energy from the leaves to sustain root growth. In effect the roots are'ring barked'. This is shown in Figure 4.

The invention can be used as an economic solution in any situation where root growth needs to be controlled such as in plants grown in close proximity to underground infra-structures such as drains, underground services, building

foundations and roads where root growth can cause expensive damage to such infra- structure.

By the suitable choice of bag volume or soil liner volume highly vigorous potentially large plants such as invasive shrubs and trees can be dwarfed to the size appropriate to the space available.

To halve the growth rate the volume has to be decreased by a factor of ten. Plants of all kinds can be grown in the appropriate size bag above ground in the nursery and planted still in the bag into the ground.

In ground nursery stock planted in bags would be already root balled removing the need for wrenching and bagging. They are easily removed from the soil and transplanted at any time of the year without any destruction of the root system.

The results with fruit trees and grape vines is impressive in terms of growth control and fruitfulness. Apple trees grown in ten litre bags in the soil are approximately thirty percent more efficient in yield relative to their size than trees grown in large 100 litre bags or without root restriction. The smaller trees occupy only an eighth of the canopy volume of non-restricted trees. The combination of highly fruitful plants at increased planting densities can produce substantial increases in yield per hectare.

The choice of the bag size and density is an economic one which depends on cost of bags, plants, support structures and land costs. In the applicant's trials over twelve years production with apples in bags between 25 and 50 litres tend to be more self supporting than smaller volumes but still occupy considerably less space and are more fruitful than unrestricted plants. With grapes which are normally supported by trellis the weaker growing vines in 10 to 20 litres are suitable. Vineyard pruning costs and excessive fruit shading are almost completely eliminated in these smaller volumes.

The invention also offers the potential to control growth and fruitfulness in other species where no satisfactory dwarfing rootstock exists at present.

Finally the increase in the efficiency of fruit production per unit of water and nitrogen used with root restriction could have major advantages where water and nitrogen availability are the limiting factors in production.

The invention has the potential to cheaply reduce the destructive effects of root growth on underground infra-structure, grow plants to fit the space available and control the growth and increase the biological efficiency of fruiting trees and vines per unit of ground area or unit of water and nutrients available.

As far as the inventor is aware no comparable product is currently under patent or available utilizing volume, hole size, hole density or as robust as the material of which the bags or soil liners as described in this application.

It is to be understood that the scope of the invention is not limited to the described embodiments and therefore that numerous variations and modifications may be made to these embodiments without departing from the scope of the invention as set out in this specification and claims.