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It was a train trip six years ago that lead to a change in lifestyle for Ruth and Alec Tasker and family. Hopping off the train at Oamaru to visit friends at Kakanui, Ruth and Alec were told of a tomato growing property for sale.

At that time, the Taskers were share-milking 400 cows at Clinton in Southland. But Alec felt that the share milking commitment didn't allow him time to take his children to sports and be involved in church activities. Even though the two hectare property at Kakanui was run down and was going to require a huge input of energy and finance, the Taskers could see potential for development to grow a variety of fruit and vegetables.

When the Taskers took over the property, even though they lacked experience in tomato growing, they expanded to 6000 plants, picking three tonne a week.

"Learning to grow tomatoes was a challenge and market prices were poor. With only one good year of returns in the first four, I felt the market wasn't looking after us, so I decided to pull down a large glass house to allow space to expand into other crops," says Alec.

Alec and Ruth retained just 1000 plants to supply tomatoes locally. These plants are layered and grown hydroponically, using two 100 litre containers, one with calcium and the other with nutrients. Although not certified as organic, Alec dislikes hard chemical sprays so he applies soft soap to control tomato pests.

The next challenge for the Taskers was expansion into cherry trees but not before Alec had researched the market and received advice from local grower, Fred Field.

Contrary to conventional thinking, Fred advised them to look at growing trees and plants in bags based on a strategy of root restriction. "A plant or tree re adapts to what's available. If it's very dry, a plant won't expend energy seeking something that isn't there. In turn, this will govern the activity above the ground. When roots are restricted they stop producing rootstock," Fred explains. "The size of the leaves becomes smaller to restrict transpiration, woodstock production is reduced, and reproduction becomes the prime function.

"So, bag control provides a grower with the advantage of a minimum of pruning, higher yields per hectare, and I have found that bagged trees can be moved into glass houses for early production or held in chillers for late production.

Following that research, the Taskers established new shade houses for 2000 cherry trees of five varieties: Burlatt, Roseanne, Stella, Lapins and Summit, contained in bags in the ground. “The size of the bag determines the height of the trees, with most of ours growing up to two metres”.

“These bags last the lifetime of the tree. Some of our trees are now three years old and will fruit for many years”, says Alec.

However, Fred advises that good potting mix or soil mixed with fine bark and humus is needed in the bags.

"It's also important to place a layer of coarse sharp sand 25 mm deep on top of the soil or use pebbles; this slows the drying out and facilitates a more even distribution of water when applied”.

He suggests 10 litres of water per week for a bag with a 20 litre capacity, but after leaf fall 10 litres per month is sufficient. It is essential not to over-water. When trees in bags are being grown on top of the ground, Fred also suggests using recycled silage wrap to provide ground cover to stop weeds and roots escaping out the bottom.

At Kakanui, cherry trees flower in August/September and fruit just before Christmas until mid February. Cold easterly winds and frosts can be a problem for Kakanui growers, however the trees need 1400 hours of chilling to help the fruit set.

Alec says the trees don't require a high maintenance input, although they do need to be pruned in December, and fertilised once or twice a year. This year, Alec has also applied a copper spray for the first time. In winter, he clears the grass around the trees and lays sulphur to eliminate pear slug and aphid, although he also works to maintain a ladybird population to control aphids.

Further expansion during the past season has been the growing of 1600 strawberry plants in long cylindrical bags filled with untreated sawdust. Set out on benches at table height, these are grown hydroponically. "Being our first year, it's been quite a successful experiment in 80 percent of the plants," Alec says. "However, next year, we will have fewer bags to give the leaves more space which will also allow better flowering."

Harvest season for the strawberries is from the end of November until late April, and the plants will have a fruiting life of two to three years. The Taskers have been pleased to find they haven't experienced pest problems and, other than the time required for picking, the plants don't require much attention through the fruiting season. When the weather cools and frosts begin, the crown of each plant is removed to promote new growth.

Fred Field says that strawberries can also be grown in a long ground bag by mixing good quality soil with rotted sawdust and liberal amounts of horse manure. The plants need to be in a sunny position placed 200cm apart. As well as tomatoes, cherries and strawberries, the Taskers' grow Washington greengages in bags, and next year they will have six varieties of red peppers as well as already established tree tomatoes, zucchinis, raspberry bushes, cucumbers and an avocado tree all in bags. Alec concludes with a small warning that while he likes experimenting, it's important to remember there's a lot of reality to land ownership, and experimentation has to be balanced with turning a run down property into an economic unit.



Bonsai Bags are designed to restrict root growth and as a consequence control the growth rate and fruitfulness of fruiting and ornamental plants. The growth rate decreases as the size of the bag decreases. Fruitfulness increases as the bag size decreases. Research has shown that decreasing the bag volume by four-fold decreases the growth rate by half.

The bag has been designed to be used above ground or buried in the soil. The plastic of which the bag is made is ultraviolet light stable and should last for ten years when exposed to light. Buried it should last indefinitely.

The density of holes in the bag slows drainage rate of water applied to allow even distribution of water within the soil in the bag without causing water logging problems.

The diameter of the holes is such that they prevent roots of most plant species tested escaping from the bags when buried in the soil. Even where a species can produce extremely fine roots that can penetrate these holes, the diameter of such roots is so small that the frictional costs of water passing through them to the leaves is so great they are functionless in terms of water and nutrition uptake. Small roots of this size do not undergo secondary thickening and tend to be ephemeral. When used above ground, pruning ensures that no roots escape from the bag. The exception is the base of the bag when the surface on which it is standing remains moist. However, these are so fine that they are functionless as described above.


While the bag has been designed to provide satisfactory drainage rate it must be emphasized that the bag will drain no faster than the surrounding soil. Therefore, sites should not be used where normal soil drainage is poor, such as shallow, heavy clay soils or where perched water tables develop.


Where normal soil on the site is well drained and has characteristics for the species growing in it, the soil from the hole dug to bury the bag may be used as a root medium. However, a well-drained potting mix is preferable if there are any doubts about the suitability of such soil. Soil medium which contains soluble clays, or clays which swell and shrink during wetting and drying cycles should not be used as these clays can block the fine drainage holes in the bag. When using artificial media it is recommended that potting grade crushed fine bark should be used rather than sawdust, as the fine bark does not decompose rapidly and therefore maintains structure for longer than sawdust. Sand may be included in the mix to aid drainage and maintain structure. Such artificial media should contain a good quality complete slow -release fertilizer mixed thoroughly into the medium.


Fertilizer should be applied annually over the life of the plant. A good quality fertilizer containing slow and fast release fertilizer should be used. Experience has shown that an annual application of approximately three to four grams per tree for twenty litres of soil should be adequate to maintain fertility. Remember that over-fertilization can create just as many problems as under fertilization. Fertilization of irrigation water can be used, but again it is best to apply a low dose rate frequently rather than very high doses infrequently.


All weed growth within the bag should be suppressed, as the roots of weeds will compete for water, nutrients and space with the crop. Mulch should not be used where it is deeper than the edge of the bag as the roots will grow through it over the top of the bag into the surrounding soil.


Fill the bag with soil or potting mix, leaving approximately three centimetres free board at the top. This aids watering and prevents roots growing over the top edge of the bag. When buried, the surface of the soil in the bag should be level with the surrounding soil, leaving the three centimetre free board above ground level. Litter which accumulates on the surface of the bag should be removed periodically to prevent roots growing over the free board.


While the volume-to-growth rate and fruitfulness relationships are the same for all species and cultivars so far tested, the absolute growth rate and size achieved will differ with each species and cultivar within a species. In any given bag volume each species or cultivar may achieve a greater or lesser size when comparing different species or cultivars. For example, the size of a Eucalyptus grandis in a 20 litre bag is considerably bigger than a cherry in the same bag. When the option is available a more compact plant is produced with spur fruiting types than with lateral fruiting types. This difference may require some adjustment in the training methods and spacing used.


Of the species so far tested, such as cherries, apples and grape, plants in 20 lire bags should be planted on a one metre spacing. This would require 10,000 plants per hectare. However, if an alleyway is required for tractor access, two metre wide rows could be left every third row, or have a specialized tractor to work over the rows. The two rows between the alleyways should be staggered under the alleyway system. Five thousand plants per hectare would be required. If larger bags are used, wider spacings between the rows would be needed, e.g. 40 litre bags would be planted on a 1.5 metre square to allow for a 50% greater growth in larger bags. Some experimentation with density may be needed with species and cultivars where we have no experience at present.


1. Accurate control of plant growth rate. Growth rate is proportional to the volume of the bag. To double the growth rate the bag volume should be quadrupled.

2. Controls the fruitfulness of fruiting plants. The fruitfulness is inversely proportional to the bag volume. The smaller the bag volume the more fruitful is the plant.

3. The bags can be used above ground or buried in the soil.

4. The small perforations in the bag prevent roots escaping from the bags when buried.

5. The density of holes is designed to control the rate of drainage of water applied. This slow drainage allows more even distribution of the water applied throughout the root medium, preventing the normal problem of soil in the centre of bag or pot remaining dry after irrigation.

6. The smaller the bag the more compact is the plant. The internodes are shorter and the leaves become smaller.

7. Conventional planter bags and pots allow root escapes through the large drainage holes in the bottom. This is potentially bad where conventional planter bags or pots are used. These escaping roots can develop substantial roots outside the bags into the surface under the bag when used above ground, making it difficult to move them without leaving a substantial part of the root system behind. This leads to an imbalance in the remaining root/shoot ratio and a major setback or death of plants subsequent to these being moved. In serious cases the attempt to move plants can result in destruction of the integrity of the container in which the plants are growing.

In addition to roots growing through the large drainage holes in conventional containers they undergo secondary thickening which ultimately blocks the drainage holes leading to waterlogging. The secondary thickening of the escaping roots can create forces sufficient to crack even ceramic containers.

8. Plants grown for any length of time in decoratively shaped pots can fill the pot so completely that it is impossible to remove them without destroying the plant or breaking the pot in which they are grown. A plant grown in a Bonsai Bag of the appropriate size can be placed in a decorative pot so that the root ball is contained within the bag only and is easy to remove from the decorative pot if desired.

9. Plants grown in a Bonsai Bag can be transplanted into a larger bag or container at any time of the year with their root systems completely intact, removing the requirement of having to adjust the balance between root and shoot-by-shoot pruning. Thus, the original size and shape of the plant can be maintained after transplanting.

10. Root-contained plants grown in Bonsai Bags are more efficient in the use of water and are therefore less dependent than conventional pots or containers on frequent irrigation. Much of the water applied to conventional container-grown plants is wasted to drainage and with it the leaching of nutrients. This wastage can be minimized using Bonsai Bags.

11. Because the whole root ball remains within the bag, even where buried in the soil, it can be easily dug up and moved to a different location at any time of the season without any preparation such as wrenching or dislocation to the health, growth and fruiting of the plant. Because the root system of plants grown in Bonsai Bags are solely contained in the bag, plants can be grown in close proximity to each other without any one root system dominating another and out competing its neighbour. The Bonsai Bag plants don't even know that another plant is in close proximity.

12. The Bonsai Bags or soil liners prevent the major destructive potential of plant root growth on underground infra structure, and are therefore particularly suited for growing plants in urban landscape settings where unrestricted plant roots compete destructively with under ground services such as water, gas, sewerage and drainage networks, communication cables and building and road foundations, These underground services are part and parcel of modern urban living and present a major conflict for city planners when the demand for infra structure services clashes with the requirement for greener urban landscapes. This is a major problem in every major city in the world.

13. Bonsai Bag grown plants offer a new approach for landscape design, allowing virtually any species of plant to be used in conjunction with each other, with better utilization and contrast in garden design for small spaces. It also offers the opportunity to develop mobile garden design where plants can be rearranged in time, space and season because of the case of plant portability created by the container system.

14. Because plants in Bonsai Bags are so portable, plants used in orchards and landscape designs have the added attraction that they have capital value separate from the location in which they are planted. They can be traded at any stage of their growth or age and relocated. In the case of orchards grown under this system, a fully productive orchard can be moved to a new location without destruction of their growth or productivity. Ornamental plants under traditional methods are fixed to the soil where originally planted. Bonsai Bags would be just as mobile for relocation as their owners, their pet animals or furniture.


Root restriction, or Bonsai, is a method which developed over 1000 years ago in Japan. Bonsai enabled people to enjoy shape, form and a large quantity of trees in small spaces at one time. Some examples of bonsai trees are over 800 years old. Most examples were conifers, maples, chestnut & acers. The emphasis was on these rather than fruit, as large fruit on a small tree looked a bit incongruous.

Root restriction can be obtained or attained in several forms.

1. Binding the roots in a container

2 Growing on a cliff face

3 Minimising the available water

4 Growing in a hostile environment

5. Use of paclobutrazol, hormone restriction cultar.

Nature plays a role in how roots perform. If it is very dry the plant certainly won't expend energy seeking something they instinctively know isn't there. In turn this will govern the activity above the ground. The obvious actions that take place when roots are restricted are usually as follows:

1. They stop producing excessive rootstock

2. The size of the leaves are reduced to restrict transpiration

3. Woodstock production is reduced.

4. Reproduction of the species is paramount if times do not look promising. This is one of the prime functions of any plant in order to protect the species.

Three principles of bag control

Professor Richard Rowe's principles work as follows:

• Plastic bag with perforations of small size, which won't allow root development outside the bag, but allow moisture penetration or drainage. This method is based on precision calculus on what a tree can do and why it reacts to the conditions imposed on it. Put into selective soil areas would work very well as already proven.

• Field hort bags approach from a similar position of growing in a bag, but above the ground, on the condition that certain other factors are adhered to. For example, reliable, evenly distributed water can be supplied (on average 10 litres per week). This system is complimented with outer chutes, which work well on slight slopes or flat ground if good drainage holes are in place.

• The last principle is cylinder bags made from heavy grade shadecloth, but still effective in extreme dry areas or inserted in ground through holes in complete film ground cover. The tree sometimes assumes it is trapped with little room because the fine fibres of the bag may suggest to the roots that it is another competitive set of roots nearby. We know that roots of one tree know the whereabouts of another; they do not fight for territory but share. There are only a few trees that dominate areas. Eucalyptus is one that does this by poisoning the soil and thus prohibiting other plants. Other evergreens sometimes root graft onto other deciduous trees.


Professor Richard Rowe, who travelled down from Christchurch for the event, gave a fascinating overview of his career to date, highlighting instances of bureaucracy where they displayed "idiocy of the first order suggesting that grapes could only be grown in Auckland”.

He also pictorially described what glasshouses looked like when the trees were left to grow unchecked - "the insides of a cows stomach at midnight".

Richard initially became involved with root restriction research when he was asked to help discover why pear trees survived floods in Europe and peach trees did not.

It was this intensive study that led Richard to become very interested in root structure and how it relates to the above- ground aspects of the plant.

Later in his travels around Europe, Richard viewed dwarf apple trees planted post WW11. This led him to believe that contrary to common held beliefs at that time, big trees did not equal big yields.

The dwarf apple orchards of Europe displayed high yields and productivity, required little pruning and were planted at high density, unlike previously established orchards in the UK that were managed with more traditional methods, which showed less productivity and lower yields.

This experience led Richard to delve into the science of miniaturising trees, or the art of Bonsai. During one of his visits to the Emperor of Japan's inner gardens, Richard viewed Cryptomeria trees that were 800 years old. This was a tree that normally only survived for 200 years in a forest. Richard was intrigued how did it work?

What Richard discovered was that Bonsai is miniaturisation in scale: the growth rate is proportional to the volume of soil in which it is grown

Richard then trialled growing trees in bags. He discovered that the fruitfulness of a tree decreased as the volume of soil in which it was grown increased.

Additionally, Richard noted that fruit growing on trees in bags was much larger than anticipated. This led him to believe that fruit size is independent to the size of the roots of the tree, and regardless of species or genetic makeup. The tree's energy is used to feed fruit, not wood & leaves.

Richard came to the conclusion that you can double fruit production by reducing the volume of soil in a container by four.

After 35 years of research it became apparent that the success of trees in bags came down to physics, not biology, and the relationship between diameter and pressure.

Basically, roots of a tree will not pass through a pore size (or hole in a bag) smaller than its own diameter. The root follows the path of least resistance then stops growing when it hits a pore size smaller than its current diameter. What is does next is to grow laterals. So roots of trees in bags are naturally contained by the above process (which is in effect pruning of the roots). The root will not continue to circle the bag becoming root bound, but will naturally stop growing, thus affecting growth and fruit size above ground.

Richard has determined the smallest size necessary for the holes in a bag, and has developed a bag which will allow this system to work at its best. He has patented this bag and is selling them through Field Horticulture. Richard also discovered that the secret of Bonsai was not root pruning (manually) as he thought, but the size of the container in which it was grown.

Richard also outlined the necessity for oxygen (by aerating soil) within the bag to encourage effective drainage of the soil/media mix. Good drainage is also a requirement for healthy plant roots.

A discussion was had on types of media, with Richard suggesting well rotted manure with bark/sand mixes over sawdust, which he felt was too demanding on nitrogen.

Richard discussed fertilisers and felt that "a little often" is better than heavy coverage .The plant will use what it needs, the rest will be wasted. This runs the risk of leading to long term salt problems”. Richard suggested that sometimes the problems displayed by plants are actually due to overwatering, not underfertilising.

Richard explained how leaves were protein driven and need nitrogen, whilst fruit was sugar driven and underwent a different set of biological processes to the rest of the plant. However, he made the comment that although subject to different processes “the fruit growth is an indirect result of what the leaves have achieved with nitrogen". Richard suggested that 20 Litre bags would be suitable for growing in, with a planting ratio of 5,000 trees per hectare being achievable.

Fred spoke next on the need to eliminate weeding and pruning from the orchardists 'to do' list. They were time-wasting activities, not income-producing activities.

Fred discussed how his research here has shown how "Oamaru is naturally late for cherries". Fred commented that many local growers were tempted to pick early when the cherries had coloured up, but too early for the sugars in the fruit to be high enough. He suggested that they need 140 days from flowering to picking. This is a lot longer than what is experienced in Central Otago.

Fred displayed his very successful crop of cherries this year, indicating how some were too large to be measured by traditional means.

Fred's discussions with clients have shown that what people want with a cherry is taste and firmness. Fred suggested that "we eat with our eyes".

Fred discussed the need for local growers to price their fruit accordingly and value their produce. The last growing season was discussed, with Fred outlining that we experienced one of the warmest Septembers remembered, followed by a very cold October and cloudy November. This led to little photosynthesis occurring and was evidenced by deformed pits inside the fruit. These fruit were often affected by Botrytis later in the season. Fred outlined his thought that trees are good predictors of droughts and are able to survive by fruiting heavily. Richard reiterated this fact saying that in effect root restriction was an 'inherent drought strategy' used by the plant which must 'reproduce to survive'.

Overall, the comments that Fred and Richard made were valuable and thought provoking. The visual examples that growers could see of small trees fruiting heavily in bags were backed up with scientific reasons as to why this happened, with the tree suffering few ill effects from water and root restriction.

This article was supplied courtesy of a New Zealand Company called Field Growe Bags LTD. If you live in New Zealand and would like to purchase their bonsai bags please visit them at this web address:

If you are in Australia Daleys Nursery stocks bonsai bags which can be found here:

Bonsai Bags