The Olive
Scientific Name: Olea europaea
Family: Oleaceae
Reprinted from: The Tree Cropper,
Issue 6, December 1995
The
olive branch is an historical symbol for peace and is today depicted on
the United Nations flag. The olive tree is long-lived with some
specimens over a thousand years old. The olive oil industry was under
way 5000 years ago, and is still flourishing today. This is an
incredibly old and stable industry which can make a very real financial
return for those who choose to pursue it. The olive industry is not
now, nor ever will be, a golden Eldorado, rather a consistent provider
over a very long term.
Climatic requirements
Olives
and grapes have similar soil and climatic requirements, but with the
olive tolerating rather more severe conditions. Olives should have
long, hot, dry summers to ripen the fruit, and cool winters. Some
cultivars, such as those grown in Crete, southern Greece, Egypt,
Tunisia, Algeria and Israel, bloom and fruit with very little winter
chilling. Those originating in Italy, Spain and California require more
chilling for good fruiting. As far as frost is concerned, -8° Celsius
is about maximum for most cultivars, though some can definitely
tolerate more than this.
The
major
difference between New Zealand and the Mediterranean is that New
Zealand is a series of islands with large areas subject to persistent
winds. Any tree will grow better out of the sand, and for this reason
orchard-type shelter is recommended.
Soil requirements
Although
olive trees readily adapt to a variety of soil types, they prefer light
rather than heavy, and well-drained rather than water-retaining soils.
The olive tree will grow and bear on poor, shallow or gravelly soil
better than most orchard species. However, keeping the grove
well-fertilised, especially with nitrogen, is recommended to maintain
an acceptable level of production. Olives prefer a pH of 6.5 to 7, and
a fertiliser regime to keep other nutrients in balance can be
determined by leaf and soil analysis.
Water requirements
With
tough, leathery leaves which do not transpire readily, the tree will
fruit well on a lower water supply than other orchard species.
Nevertheless, light irrigation over a dry summer will be beneficial.
This is more important for table olives than oil producers.
Grove layout
There
are many recognised spacings for planting. However, in New Zealand
where the soils are generally fertile and moisture levels are adequate,
either naturally or with supplementation, intensive planting is
recommended, with spacings of 3m between the trees and 6m between rows.
This way the trees will shelter each other, and you will make maximum
use of land and light, which will lift both quality. and yield. This
system suits mechanical pruning and harvesting, achieving a substantial
reduction in costs.
Olive
grove set-up costs are low but there is a period, before the trees
fruit, when there is no income from the planting.
Grove maintenance
Although
the olive is a very hardy and durable tree it requires the same care
and attention in its early years as any other species. Keep the area
around the young trees clean of weeds, either by hand or by careful use
of a herbicide (Roundup at 1 % has proved satisfactory). Don't ever use
a pre-emergency spray. Spraying for pests and diseases is not usually
needed.
Training and pruning
The
aims of tree training are to accelerate tree growth, promote early
fruit production, and maximise returns. An important principle in
pruning olives is not to do formation pruning until the first decent
crop has been harvested. Until then, simply remove the shoots which
sprout below the half-metre mark. Severe pruning during the early years
depresses growth, delays the start of bearing and reduces the volume of
the first crops. Good training will simplify later pruning operations,
and adapt the tree to future mechanical harvesting. If it is done
properly, little pruning is needed later.
In
general, pruning starts once harvesting is over. Pruning should be
avoided during winter months in high frost-risk areas, since the larger
plant mass on the unpruned trees provides a protective screen. Recent
trials have shown that it may be wise to let more than two years lapse
between one pruning and next. Three-yearly pruning may reduce the
two-yearly alternate harvest patterns which pruning often heightens.
Tree shapes
There
are two simple proven training systems.
•
Vase shape. The traditional method for extensive plantings is for an
open centred vase shape, with three to five main scaffold branches and
an open centre.
• Mono-conical shape.
Modem intensive planting suits a mono-conical shape with a central
leader and tip ascendancy.
A. Vase shape
1
Pruning is virtually non-existent during the non-bearing period and
until the first abundant crop has been harvested. Until then, simply
remove any suckers that may sprout at the base of the trunk. These
should be removed in the summer, as often as is necessary and while
they are still tender, so you do not produce any unnecessary wounds. If
any branches lower than the planned crotch position are becoming too
vigorous, they should be shortened back a little. Do not remove them
altogether, as this will lower the leaf/root ratio and also markedly
restrict the circumference development of the trunk.
2
The first real formation pruning should be done after the tree produces
its first large crop. Make the crotch about 0.6m - 0.75m above ground,
with three to five main branches evenly spread. Crotches that are too
high lower tree productivity. Naturally, pruning should not be so
severe as to upset the tree by drastically modifying its leaf/root
ratio. The vase shape should be achieved through successive prunings,
never in one go.
B. Mono-conical shape
This
is similar to the central leader system adopted in fruit orchards, with
the central leader kept upright. It is the shape most frequently used
in new orchards in central Italy, and will probably suit intensive
plantings in New Zealand to give the highest per hectare yields. It is
easily achieved and requires little pruning, especially during the
non-bearing period. It provides a larger outer fruiting shell for the
light to penetrate. In addition, it is the best shape for fruit
harvesting using trunk shakers, and offers less wind resistance.
First year:
During the summer the lower branches, up to 35cm off the ground, should
be either tipped or eliminated. This encourages the plant to grow
upwards during the autumn.
Second and third years:
Pruning should be kept to a minimum, being confined to removing very
low branches (up to 45cm off the ground) and any inner upright-growing
branches that might compete with the central leader. Make sure that the
branches issuing from the central leader are arranged in a spiral, so
that maximum advantage is taken of light penetration. By the end of the
second year, the conical shape will be more and more obvious.
Fourth year:
When the first fruit has been picked, prune as you did in the preceding
years, the primary object being to establish the central leader. If the
central leader is too high and flimsy in relation to the trunk size,
simple cut the top out. At a later date a new leader can then be made
out of a vigorous growing branch. Any branches below about 75cm can
come right off.
Fifth
year:
Remove any weak twigs that appear on the lateral branches. As well as
preserving the tip ascendancy of the leader, successive prunings should
ensure that the laterals spiral round the trunk, decreasing in length
from the base up to the apex to produce a cone. When training has been
completed, the tree should be no more than 4m tall. If any higher, it
can be lowered by cutting the leader and tipping the laterals.
Young bearing period:
Between the sixth and seventh year the plant usually acquires its
desired shape and achieves a balance between its vegetative and
productive activity. During the juvenile stage vegetative growth
predominates and the tree grows rapidly. As fruiting increases, the
tree finally achieves a balance between growth and fruiting, which must
be maintained.
Machine
pruning
This
method of pruning on mature young orchards using a multi-disc tree
topper is used in Italy and California with good effect, and has given
promising results in trials in Spain. It is now being tested in New
Zealand at Marlborough Olives.
Harvesting
Light
crops begin after 3 to 4 years. In the first few years of fruit
bearing, and until the root system is well-developed and the tree well
anchored in the soil, harvesting will have to be done by hand.
Hand-picking is the system which gives the best quality oil. When
older, trees may be harvested by mechanical shakers. With high
producing cultivars a yield of around 10 tonnes per hectare can be
expected before the grove is ten years old.
Olive oil production
This
is the only vegetable oil that is made by simply crushing the fruit,
with no further treatment required, and some oil presses are already in
use in New Zealand. Choice of cultivar, growing location, harvest
timing, quality of olives and pressing technique all influence oil
quality, which is judged by the oil's acidity and flavour. Colour does
not influence flavour, so is not an indicator of quality. The
International Olive Oil Council (I.O.O.C.) has a standard scientific
test to determine the purity of the oil. The best oils have an acid
content of under 1%. In tests performed by the Cawthron Institute at
Nelson over the last 5 years, some New Zealand samples had acid ratings
which varied from 0.25% to 0.5%, putting New Zealand oils in the deluxe
bracket on a world scale for purity. These high-quality oils come only
from the first pressing of top-grade, carefully handled olives.
Most
olives are pressed into oil, because it is much simpler, faster and
cheaper to press. Olive oil's image has improved in recent years
particularly because of its cholesterol-reducing capabilities, and
consumption has grown. Table olives also have their place, but take
longer to establish on a large commercial basis. Producing table olives
can be more profitable, but the processing is also more complicated.
Olives
suitable for pressing were fetching $l/kg in the Marlborough area in
the 1995 season, but it is essential that you apply all the technical
breakthroughs made in variety selection, plant training, grove layout
and mechanisation, if you wish to obtain high per tree and per hectare
performance, good oil quality, and a low-cost, high-profit structure.
Varieties
Cultivars
should be selected only from the very best available. New Zealand is
fortunate to have access to superior stock at the beginning of our
industry. The I.O.C.C. world collection of trees growing at Cordoba,
Spain, are the very best specimens obtainable from their country of
origin. Out of 169 cultivars, 12 were selected for conditions in New
Zealand. Eight more varieties were obtained from the agriculture
research organisation of the Government of Israel, and two from
Visalia, California.
These are all listed below with
their
country of origin, and include both table olives and oil producers.
Production and oil yields quoted are averages for those varieties in
the country of origin. Several of the cultivars may be suitable for oil
production in New Zealand conditions, and considerable interest is
being shown in Barnea, Manzanilla and Picual.
Barnea
(Israel). A high producer with little alternate bearing. It grows
erectly and quickly, coming into production very early with
medium-sized, slightly pointed fruit. The oil is of high quality, with
a yield of above 20%. When mature it can produce crops of over 70 kg
per tree, giving 15 tonnes per hectare. This cultivar was developed to
meet the needs of modern intensive olive groves and is a truly
commercial cultivar.
Manzanilla
(Spain). A relatively small tree with a spreading canopy, it is highly
productive and early-bearing, and is the world's most popular for table
olives. It is normally harvested green, which partially offsets its
natural alternate bearing. It has a good flesh-to-stone ratio with an
average oil content of good quality. Mature trees may yield up to 50
kg. It has medium resistance to cold and Peacock Spot.
Uovo di Piccione
(Pigeon's Egg) (Italy). A small, slow-growing tree much sought after
for its jumbo-sized fruit ideal for pickling. Oil content is low. A
characteristic feature of some varieties, such as the Uovo di Piccione,
and the Souri, is their small size, but these trees can nevertheless
bear heavy crops and possess other desirable features. Ouvo di Piccione
and Souri are both susceptible to Peacock Spot.
Souri
(Israel). A slow-growing small tree, but very sturdy. It has a low
chilling requirement and likes a dry climate. It has a medium-sized
fruit, with an exceptionally high oil content of very good quality.
Nabali Mouhasan
(Tunisia). A fast-growing tree with a wide canopy. Many produce
commercial crops four years after planting. Medium-sized pointed fruit,
oil content of 20 - 50%.
Picual
is a Spanish variety, number one in oil production, with a percentage
yield similar to Barnea. Very early fruiting, productive, hardy,
tolerant of frost and of retained moisture in the soil.
Morailo, Leccino and Frantoio
are all well known in Italy and important producers of high quality
oil. They are all cold-resistant, but Morailo requires lower winter
temperatures than do the other two. Leccino needs a pollinator, while
Morailo and Frantoio are self-fertile. The fruit of Morailo has a
strong attachment to the tree and can't be machine harvested. Leccino
is resistant to Peacock Spot.
Koreneiki
(Greece). Small and shrubby, but hardy enough to grow in extremely
marginal soil and arid conditions. It bears a large OfOP of small
fruit, and is a good producer of high quality oil. It has very low
chilling requirement and is resistant to Peacock Spot.
Chemlali, from
Algeria and Tunisia, is similar to Koreneiki.
Some
other varieties are: Carolea (Italy), Hojiblanca (Spain), Sourani
(Syria), Kalamata (Greece), Picholine (France), Kadesh (Israel), and
Mission (USA).
Pollination
Most
olive varieties are self-fertile and do not need pollinators. However,
some will perform better with the aid of a pollinator. For example,
Manzanillo, which has an acceptable level of pollination in the
traditional growing areas of Spain, benefits from cross-pollination in
the growing areas of California, Argentina and Italy.
In
Israel
it is a necessity. Ouvo de Piccione is regarded as a suitable
pollinator, but in Marlborough and Canterbury, Manzanillo appears to be
self-fertile.
Sources
of information
This
is article is based on information contributed by Hamish Macfarlane, of
Marlborough Olives, much of which came from the I.O.O.C. magazine,
"Olivae". The information on pruning has been taken mostly from the
International I.O.C.C. practical handbook on pruning. Extensive use has
also been made of the Olive Grove library.
The Olive
Grove was
established eight years ago at Blenheim by Gidon and Triska Blumenfeld,
and was the first olive grove of its size to be set up on a commercial
basis in New Zealand. After Gidon's untimely death in 1991, Triska
carried on for the next three years. She then sold the grove to Sue and
Simon Morris and Jane and Hamish Mcfarlane, now trading under the name
of Marlborough Olives.
Further information can be
obtained from
some of the books on olives listed in the green pages of this journal,
and from the NZTCA Olive Action Group. This group is again fully active
and can be contacted though its secretary. Jennifer Bradshaw, 31 West
St, Greytown. With the assistance of our Tree Crops Research
Coordinator, Roy Hart, the Olive Action Group has obtained most of the
above varieties from Marlborough Olives, to establish trial plots and
further test varieties and yields in different locations. There also
appears to be interest in olives in the North Island, particularly in
some parts of Northland.
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