RESTRICTION IN CHERRY TREES
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An article from Rural Delivery, June 2007.
Root restriction, or bonsai in Japan, was developed over 1000
years ago in Japan. It enabled the enjoyment of the shape and
form of trees in small spaces. Some examples of bonsai trees
are over 800 years old. It was used for conifers, maples,
chestnuts and acers, rather than fruit trees, as large fruit
on small trees looked incongruous.
Now root restriction for smaller tree size is being applied to
horticultural crops for some fundamental reasons:
Growers control the orchard rather than the other way round.
Higher sustainable returns per hectare, with the option of
leasing land rather than owning.
Lower cost of protective structure against birds, wind and
The option of moving the trees to a new location.
Fred Field is a horticultural consultant in Oamaru, with a
nursery, who has been advising people on how to set up cherry
orchards under cover on small land holdings.
He makes and sells bags from Polypropylene, called Growe bags.
The most common size is 10 litres, which results in about 100
litres of tree canopy. Root restriction produces that 10 to
one relationship, plus a correlation between the diameter of
the bag and root ball, with the canopy diameter. Thus a long
thin bag will result in a thin tree. Fred believes about 150
people have started orchards using Growe bags, which control
the woodstock while encouraging fruit production. Fred claims
fruitfulness is inversely proportional to the size of the bag,
so that root restriction actually increases fruit yields.
Most bag orchards are above ground, requiring some sort of
running wires to which the trunks of the trees are attached,
to prevent blowing or falling over.
The small orchards are covered with shade cloth to protect
from birds, hail and frost. The plants also become more
compact, with the internodes shorter and the leaves smaller.
That means they stay at workable height, without the need for
ladders or hoists.
Surprisingly, Fred does not recommend irrigation or
fertilisation, because he says the plant will regulate its own
development to the available nutrients and rainfall.
“Plants in the right environment will photosynthesise all
their own nutrient needs,” he said. With minimum added
fertiliser, the plant builds smaller structures, which is the
whole point of the root restriction.
For the peace of mind of growers, Fred’s irrigation
recommendation for plants/bags above the ground, is no more
than one litre per tree per day. If growers intend to put the
bags in the ground, then he warns against heavy, clay soil
surrounds, which he says just creates a pot in the ground,
resulting in water-logging.
Other advantages of Growe bags include reduced pruning of
trees, possible manipulation of seasons, by moving trees into
glasshouses for early production, or leaving in chillers for
late production, higher yields per hectare, depreciation
options, with capital investment in a tangible asset.
Among the disadvantages are slightly higher set-up costs for
bags, wires and covers etc., all offset by reduced long-term
management work required for smaller trees versus larger ones.
The average cost of a Growe bag is $3, made from cloth which
will not rot.
Plants grown in a Growe bag can be transplanted into a larger
bag or container at any time with the root system completely
intact. That removes the need for shoot pruning and the
original size and shape of the plant can be maintained after
Because the root systems of plants grown in bags are
contained, plants can be grown in close proximity without any
one root system out-competing its neighbour.
Fred is also experimenting with cambium restriction, using
pressure bands, which mimic some of the physical effects found
in nature, when a branch folds over and hangs down, resulting
in more fruit. This is notable on pears and plums.
Fred has about 1000 trees in bags or with cambium restriction,
of many different types. Maudes Rd is an experimental site, as
well as a Growe bag nursery. He founded Tunnelworld crop
canopies, in which he was involved for 20 years, and then
about 15 years ago began the work on root restriction. He has
been closely involved with Lincoln University horticultural
department, but no longer purchases any work there.
Work is being done overseas by researchers on big commercial
crops where orchard space is limited, but there is little
official research work in New Zealand at present. Field
Horticulture is pretty much a one-stop shop for the theory,
bags, plants and advice.
With cherries, the major crop being grown under root
restriction, Fred predicts that one square metre tree canopy
diameter will result in four to five kgs of fruit per season,
which at the minimum price of $10/kg returns $40/sg m, which
is high for any horticultural venture. Because of portability,
plants in Growe bags have a 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. A fully productive
orchard can be relocated without loss of growth or
Root restriction is currently being applied to cherries,
apples, stonefruits, pears, plums, citrus, feijoa, avocados,
roses, rhododendrons, potatoes and strawberries.
Ornamentals are also grown in Growe bags with root
restrictions, which open up new options for landscape
gardening. Virtually any species of plant can be used in
conjunction with each other, for better utilization and
contrast in garden design for small spaces. Plants can be
rearranged in time, space and season because of easy
© 2007 Showdown Productions Ltd.