Olive
Cultivation
The most popular article in the MGS journal, The
Mediterranean Garden, has proved to be one about pruning olive trees.
It seems that gardening in a Mediterranean country goes hand in hand with
growing olives – from planting a new grove to tackling one or two neglected
trees. So here in their entirety are the three articles about olive cultivation
which have appeared in TMG in the past followed by lecture notes from an olive
expert who gave a workshop at the 2007 AGM Symposium.
Photographs by Davina Michaelides.
Pruning Olive Trees by Brian
Chatterton
From The Mediterranean Garden No 34 July 2003
Olive Oil Production by Brian
Chatterton
From The Mediterranean Garden No 41 July 2004
Organic Olivesn by Chevrel Traher
From The Mediterranean Garden No 47 January 2007
Training and pruning olives by Dr.
Peter A. Roussos, Laboratory of Pomology , Agricultural University of Athens.
(Dr Roussos presented a workshop on olive pruning at the MGS Symposium: The Dry
Garden – Practice and Philosophy, Athens, 2007.)
A Greek olive grove in spring
by Brian Chatterton
From The
Mediterranean Garden No 34 July 2003
Art or science?
Most books written on olives
in English describe pruning as a mystery buried deep in ancient folklore. There
are exceptions such as Gucci and Cantini and our own book, but the majority have
failed to understand the basic principles. Books in Italian (for example Del
Fabro) are more practical and less mystical. A good pruner of olive trees can be
compared to an artist where talent and technique are moulded together. The fact
that a great artist may be a poor teacher of perspective should not disguise the
fact that perspective is a technique that can be learnt. Similarly with olives.
The techniques can be learned (the master pruner may not be the best teacher)
and a reasonably competent job done.
Why prune?
Most readers will have only a few
trees or perhaps a small grove and will pick their olives by hand or use simple
hand-held machines to speed up the task. In either case a good density of fruit
on each branch is required for productive picking. An unpruned tree will have
olives scattered in groups of one or two all over an untidy bush. Such trees are
costly and frustrating to pick. Even if you are picking with your own labour and
the unpaid help of friends, efficient picking is important. Slow work is most
disheartening. A primary objective of pruning is to produce dense clusters that
can be stripped off the tree in great showers.
It is inevitable that ladders
will be needed for mature trees but good pruning will prevent the trees becoming
excessively tall and difficult to pick. In the early days of the New Zealand
olive industry when pruning was rudimentary, one grower ended up employing the
local fire brigade to pick his tall trees.
There has been considerable
scientific research conducted on every aspect of olive growing and oil
production. One of the important facts to emerge is that the olive fruit
requires strong sunlight at every stage from fruit set to oil production. Olive
flowers that are in deep shade will not set in large numbers. Those that do will
not produce good levels of oil. Pruning is therefore needed to reduce the
density of the foliage and allow sunlight to penetrate into every part of the
olive tree. Our pruning teacher from the University of Perugia suggested that
every olive should be in direct sunlight for at least some part of the day. This
objective is compatible with the need to produce trees that are convenient to
pick. By reducing the density of the foliage one reduces the tendency of the
tree to race up and out in a desperate search for more light.
Alternate cropping.
Olives are not the only
tree crop to produce alternate heavy and light crops. Apples are as bad. The
apple tree naturally produces a large crop of small apples one year and a small
crop of large ones the next. The supermarket-driven demand for mediocrity in all
things forces the apple grower to control the trees and produce a medium crop of
medium apples. The mechanism is similar in olives. The tree produces a large
amount of vegetative growth one year and has little energy left over to form
fruiting buds. The crop is light and the following year there is a surplus of
energy to produce an abundant crop. Pruning will help even out the poor and
bumper years. My experience has been that our unpruned trees produced bumper
crops or nothing. Not a single olive. Now we prune every year and the variation
has been reduced considerably but on individual trees it can still be double one
year compared to another. The major problem occurs when some climatic event such
as a severe frost puts all the trees in the grove into the same phase. Our last
bad frost was in 1995. Now most of our trees have broken free of the alternate
cropping pattern imposed on them by frost damage. Last year a very poor crop in
one part of our grove was compensated for by an excellent crop in another
part.
Tree shapes
There are many different shapes
for olive trees throughout the Mediterranean region. Tarek Amamou’s book shows
some of the principal forms in Spain, Italy and North Africa but the differences
are slight for the uninitiated and all the diverse shapes can be simplified down
to two. The mono-conical and the poly-conical or to use less mathematical
language – the Christmas tree and the vase or wine glass. The Christmas tree is
a new idea that has no traditional basis in the Mediterranean. It was invented
for mechanical picking using the shakers first developed in California. More
recent scientific research conducted in Italy has shown that the Christmas tree
shape is no better than the vase for mechanical picking. The theory was that the
shorter distance between the main trunk and the fruit bearing branches would
transmit a stronger shaking force. Actual experimental work has shown there is
no difference in picking efficiency. The Christmas tree is more difficult to
manage. Some growers in our comune are converting their Christmas trees
to vases. The vase in various forms is by far the most popular shape throughout
the Mediterranean and the most practical for hand or semi-mechanical picking. I
would recommend it for growers with a few trees or a small grove.
There is a
third shape that is rarely found in the classic olive books (Vallerini is an
exception) which is the recovered frosted tree. In central Italy and other cold
regions of the Mediterranean all the growth of the olive tree is frosted off
above ground at roughly thirty-year intervals. This is when a particularly
severe Tramontana blows down from Siberia. Suckers shoot from below
ground and three or four are selected as new trunks. They form a ring of new
trunks around the stump of the old stem of the previous wineglass-shaped tree.
If the tree is frosted again these multiple trunks die and again suckers are
selected to form new stems. Each time a severe frost occurs the ring of multiple
stems moves further and further out leaving a larger dead stump in the
centre.
Young trees
Most small growers will purchase
one or two year old trees to establish their grove. These are roughly a metre
high, are sold in a small pot and cost about Euro 5 each. These trees will need
to be shaped. It is possible to buy larger trees. Trees up to fifty years old
are available from our local nursery but they cost over Euro 500. Even a few
additional years of growth can be expensive. The price approximately doubles for
each additional year and with each re-potting. These older trees are shaped.
The pruning of young trees follows two contradictory principles that must be
balanced. The first is to shape the tree into the form that, except for frost
damage, will be its structure for life. The other is to allow the young tree to
grow and build energy reserves. An old tree can be chopped and hacked with
impunity and will rebound with enormous vigour from the energy reserves in the
roots and trunk. The young tree will not. A determination to form the perfect
shape by excessive pruning will weaken the young tree and stunt its growth for a
number of years. Achieving the right balance is part of the realm of art and
talent that distinguishes the good pruner from the also-ran.
Cocktail glasses and dry martinis
The shape
of the olive tree is loosely referred to as a vase or wine glass but it is
necessary to be more precise than this. It is actually one of those silly
cocktail glasses that were common in Hollywood movies of the nineteen-thirties,
when smart people drank Dry Martinis from little glasses containing rubber green
olives on a stick. These glasses were open at an angle of ninety degrees. It is
certainly not the shape of a Champagne flute. The whole point of the wine glass
shape is to let in the light and allow the sun to shine on the fruit during the
middle of the day from the inside through the hollow centre. A flute glass will
not allow as much penetration of light into a mature tree as the wide-mouthed
glass.
The young tree purchased from the nursery has a central stem and a
number of lateral branches. The objective is to select three or four of these
laterals to grow up and out to form the structure of the glass. At a recent
pruning refresher course run by our local comune there was much
passionate debate about the merits of three and four arms which I cannot claim
to be expert enough to understand. I have taken the soft option and allowed the
tree to decide. If there are three good laterals I use them; if there are four I
leave them. Occasionally there are only two. Then I need to find two more (a
year or so later) on each of these for an eventual structure of four arms. There
is also some debate about the height of the crown – that is the top of the stem
in our cocktail glass simile. As far as I can see, except for the aesthetics of
having a nice row of even trees it does not matter much between 80 and 120 cm.
If you intend to use a shaker for harvesting the trees when they are mature 80
cm is too short and a minimum of 100 cm is needed. Having selected your three or
four arms from upward growing laterals there is no need to cut the others off.
You only need to ensure they are growing out and down – not up, as I will
explain later.
The arms that you have left will not grow into that perfect
cocktail glass shape. Olive trees are never that obedient. More corrective
action is needed. They will naturally shoot straight up into a flute glass
shape. To push them out requires constant topping. The upward shoot is cut at a
point where there is another growing up and out. The relentless upward growth is
halted and replaced by another. The upward growth becomes a zigzag of up and
out, up and out. As the trees start to crop the weight of the fruit will also
bend the shoots outwards.
Finally, you may need to take direct action. I was
at first very scornful of bamboo birdcages but I have adopted them as a
practical solution to recalcitrant trees that refuse to grow in anything like
the right direction. It is a simple task in a small grove to tie on lengths of
bamboo canes as spacers to push the arms into the right positions.
Renovating old trees
If you have purchased a
grove of mature trees your pruning task is completely different. If you are
lucky you will have perfectly shaped trees that have been well cared for and you
will only need to continue on the same track. It is more likely that the trees
have been neglected and will need some remedial action. I recommend caution when
it comes to reshaping the tree. Instead of the three or four arms growing out at
a nice angle of forty-five degrees the original arms may have been allowed to
split into two and then two again. Instead of three or four they rapidly turn
into eight or more. Try to get them back by all means but not all at once or
there will be nothing left of your tree. The other sign of neglect is excessive
height. Here you will need to be more ruthless. Excessive height creates
excessive shade and the lower parts of the tree will not produce fruit. You will
be forced to use longer and longer ladders to pick the olives clustered round
the top of the tree. The height must be reduced and the top shade removed to
allow the bottom part to recover its productivity.
Routine pruning
After radical surgery with a
chain saw you will need to understand routine or maintenance pruning. This
starts with close observation of the tree at picking time. You can see that the
fruit is borne on the hanging and lateral branches and not the verticals. You
will also see that some of the hanging branches that bore fruit in earlier years
have become exhausted and weak. From your observations at picking time your
should be able to distinguish three types of growth on the olive tree. There are
the strong vertical shoots that rarely produce a single olive. There are
vigorous lateral shoots that are fruitful and there are the hanging shoots. The
hanging shoots carry abundant fruit but a more careful examination shows that
some are becoming tired and unproductive.
Step by step guide
Firstly do what I call a
“clean up” of the tree. Take off all the suckers around base of the trunk and
all the shoots that have sprouted from the main arms that are blocking the
centre of the glass. Clean them off.
Now you start the hard part where more
skill and judgment is required. Your aim is to leave a single up and out shoot
on the top of each of your main arms. That is three or four on the ideal trees
or more in the neglected tree that you are trying to knock back into shape. All
the other verticals should be removed. The problem is to distinguish the
verticals. One needs judgment and experience. Some go straight up. That is clear
and simple. Others go out at forty-five degrees. These are laterals that will
bend down under the weight of olives and produce abundant crops. In between
there are all sorts of angles that you will need to make a judgement about
whether to remove or leave.
Having removed the verticals which will be mostly
around the top of the tree, you need to thin the hanging branches that have
become weak. These will be towards the inside of the tree and it is often better
to tackle them from inside the skirt of the tree. The growth of this fruiting
wood is the mirror image of the upward growth. Whereas the upward growth was
moderated into a zigzag path of out before up, the fruiting wood zigzags down.
By cutting off the last zig or zag you will allow new lateral shoots above to
replace the tired wood. Again judgement plays an important role. The dead wood
on the inside is obviously pruned off. The vigorous laterals on the outside will
produce abundant fruit. In between you must decide which should come off as weak
and which are worth leaving for another season.
Stepping back
Finally step back from the
pruned tree and look at it as a whole to judge the overall density. The ideal
tree should consist of three or four main arms coming from a trunk about 80 to
120 cm above the ground. Off these main arms are the lateral branches that bear
the crop. At the bottom of the tree the laterals are old. They were produced by
the young tree. They have grown out from the arms in a series is zigzags with
the lowest and weakest hanging branches being cut off every year. They form the
base of the cone (hence the name poly-conical) around each arm and combine to
form a skirt around the whole tree. If the laterals are long and spindly they
are chasing the light, indicating that you have not cleaned out the centre
sufficiently for light to penetrate the inside, or the overall density of the
foliage is too great. More severe pruning is needed to open up the tree. As you
move up each main structural arm the younger laterals are shorter. They are
unlikely to shade each other at this early stage but density is still important
as they collectively shade the growth below. It is important to keep the upper
parts of the tree open to allow the lower parts to remain productive, as they
are so much easier to pick.
How can you tell?
Folklore says that you
prune the olive tree until it is open enough for a bird to fly through it.
Hiding in the olive grove and watching the birds is not a very practical means
of judging the overall density of the foliage. Science tells you that you prune
until you have a leaf area index of three or four. Leaf area index is the ratio
of the area of the leaves on the tree compared to the area of ground covered by
the tree. Counting the leaves would take even longer than studying the flight
paths of the birds. Neither indicator provides an easy rule of thumb for the
inexperienced pruner. My advice is to observe other trees in your district and
to be sensitive to the symptoms of under-pruning. It is most unlikely you will
have the nerve to over-prune so under-pruning is the usual fault of the
beginner.
Let there be light
Light and more light is
the overwhelming principle of pruning. Letting the light into the tree improves
fruit production. Letting in the light also keeps the tree under control. If the
tree is dark and dense branches will race up and out to find more light.
Some useful books on olives
Amamou, Tarek, L’Olivier, (French) Edisud 1995. This
is a small introduction of only 47 pages to olives in the Mediterranean. It is a
useful reminder that of the long tradition of olive growing on the southern
shore.
Chatterton, Brian and Lynne, (English) Discovering oil –
Tales from an olive grove in Umbria, Pulcini Press, Castel di Fiori, 1999.
In spite of its title this is a practical guide to growing olives and the making
and marketing of olive oil.
Del Fabro, Adriano. (Italian) Coltivare l’olivo e
utilizzarne i frutti. Demetra 1992 This short practical guide to olive
growing is ideal for the small grower.
Fontanazza, Giuseppe, (Italian) Olivicoltura intensiva
meccanizzata, Edagricole 1998. This is essential reading for the serious
commercial grower.
Gucci, Ricardo & Cantini Claudio, (English)
Pruning and Training systems for modern olive growing. CSIRO
Publishing, Australia. 2000 An excellent guide to theory and practice including
many experimental concepts. Photographs could be much better.
Eretéo, Felix, (French) L’Olivier, Solar Nature 1988
Similar practical book to Del Fabro’s for French speakers.
Vallerini, Lorenzo (ed.) (Italian) L’Olivo nel paersaggio
agrario toscano Ponte alle grazie 1991 This is a classic for those
interested in the olive from a historical and cultural viewpoint. It also has
useful chapters on varieties and agronomy.
© Brian Chatterton
Brian Chatterton has also written an E-book about olive
cultivation.
Chatterton, Brian Growing Olives and Producing Olive
Oil. E-book, 2006. €15 + postage within Europe (request rates for other countries from
the author. Distributed on CD by Pulcini Press, Castel di Fiori, 05010
Montegabbione (TR), Italy.
This book was reviewed in The Mediterranean Garden No.
47 January 2007
A mighty tree in Aegina, Greece
Olive Oil Production
by Brian Chatterton
From The
Mediterranean Garden No 41 July 2004
The production of olive oil is a mystery. Unlike
vines where teams of pickers or large machines bring in the vintage, the picking
of olives is an inconspicuous operation. Pruning is the same. Vines are
transformed from a tangled mass of twigs to neat pared rows of almost identical
vines. One rarely sees the olive pruner at work. Perhaps there is a ladder
propped against a tree and one sees some prunings on the ground before they are
burnt or mulched. It would be a mistake to be fooled into believing that this is
a nighttime operation carried out by elves. In fact the classic olive grove is
the result of care and attention over many years. The olive trees in Umbria and
Tuscany are not by any stretch of the imagination a natural landscape. The
untended olive is an untidy bush and it is only through pruning that it has
form.
Landcare
The Italian olive oil industry is
an eclectic blend of the traditional and the modern. While the traditional
techniques receive the greatest attention in marketing, the reality behind the
scenes is often the most modern technology. Landcare in the olive grove has been
slow to adopt more modern ideas. Most Italian olive groves are cultivated in the
spring to kill the weeds and reserve the moisture for the tree. Over the years
the fertility and structure of the soil is destroyed by this excessive
cultivation. Heavy rainfall runs off and carries the soil with it. This problem
has been reduced to a limited extent by terracing but the basic structure of the
soil remains a disgrace. Some growers cultivate the soil in the autumn as well
as the spring in a vain attempt to break open the soil and allow more rain to
penetrate; I say "vain attempt" because cultivation can be effective for a few
weeks but over the years the extra cultivation is even more destructive of the
soil structure.
Abandoned grovesToday many olive groves
have been abandoned or at least are no longer cultivated in this destructive
manner. More environmentally aware olive growers have allowed the grass to grow
back and provide protection for the soil against erosion. The easy management
option is to go through the grove with a mower or better a trincatore
or mulcher in late spring and mulch down the grass and olive prunings. This will
keep the grove tidy, reduce the fire risk and leave the ground reasonably clear
for the autumn picking. If you have your own equipment for mowing or mulching
you can mow the grass two or three times over the spring period. Keeping the
grass down more frequently will encourage the growth of naturally occurring
clovers, medics and vetches that are shaded out by the tall grass. These legumes
fix nitrogen from the air and add fertility to the soil but are suppressed by
grass. To encourage the legumes further, it is a good idea to apply some
phosphate fertiliser during winter. The phosphate fertiliser and nitrogen
produced by the pasture legumes will fertilise the olive trees.
If your grove
is still cultivated or has only been abandoned over the last five years, very
little herbage of any type will grow. The cultivation over decades has not only
destroyed the structure of the soil but also the reserves of seeds in the soil.
In these circumstances you can speed up the recovery process by sowing some
medic and clover seed. For those living in Italy, these seeds can be ordered
from your local consorzio who in turn will need to contact a seed
merchant in Sardinia who specialises in seed legume mixtures; readers elsewhere
will find their own local suppliers.
SummerSummer is the period when little
happens in the olive grove. I have many enquiries from Australia and New Zealand
from growers wishing to claim tax relief on their European holidays by including
a study session on an Italian olive grove in summer. I reply that this would be
as interesting as watching paint dry and about as instructive. While summer is
a period of little activity for the grower, the dreaded olive fly can be
munching into your olives. The olive fly is a tiny midge that lays its eggs on
the olive during the summer. The eggs hatch into grubs that burrow through the
olive. The tell-tale sign is tiny air holes and of course if you break open the
olive there is the little grub. The olive fly is a permanent problem at low
altitudes as the eggs over-winter in these warmer zones. At higher altitudes the
eggs are killed by the cold and the fly must re-infect each year. We have never
had any olive fly damage in our grove which is at 550 metres. The grubs eat the
olives and reduce the yield but they also allow mould to enter and this can give
your oil a mouldy taste. The most popular form of control is traps. The
difficulty is that the flies are spread from property to property and must
therefore be controlled by the collective action of many growers. I would
suggest that a small contribution to a group scheme is a cheap and effective
means of control.
The other great hazard of summer is hail and there is
nothing one can do to avoid that. While hail is one of the many hazards of the
long-suffering olive grower, the late summer thunderstorms are welcomed for
their rain. The olive starts to produce oil in September and October in
considerable qualities and the trees benefit from rain at this time.
Time of pickingPicking in our zone begins
in November when all the summer visitors have returned to their heated city
apartments. The date for picking the olives varies from year to year but only by
a few days. This is quite different from the grape harvest and is not determined
by the same criteria. Traditionally, in our zone the olive harvest began on 25th
November or St Catherine's Day. Olive growers in other parts of the world such
as Australia who are without an olive-growing tradition find the idea of picking
on a Saint's day a fascinating piece of folk farming that has no relevance in a
modern scientific world. Scientific research does support the idea of a fixed
day, if not precisely 25th November. The reasoning goes like this. The olives
accumulate large amounts of oil in September and October. In November the rate
of accumulation slows as the days become cooler and shorter. The olives begin to
change colour but this is of no significance as green olives make the best oil
with the most flavour. In December oil accumulation stops and the olives begin
to fall to the ground. They fall slowly at first but the rate accelerates week
by week until the losses are very substantial. The date you start is determined
by when you will finish. This may sound rather strange but if the olives fall on
the ground they are wasted. Not only is it unbelievably laborious to pick up
fallen olives but they will ruin your oil as they have started to break down and
have high acidity. No more oil is being produced in December and the oil you
already have is falling on the ground. It is obvious that you should try to
finish the harvest before there are too many olives lost on the ground. One
works backwards. The last two weeks in November probably have the best
combination of high oil and low fruit loss. Further back in the first half of
November there is virtually no fruit loss but less oil will have accumulated in
the fruit. During the 15 years we have been growing olives we have noticed that
the harvest has become earlier. Growers are more interested in quality than
quantity and the early picked olives have more flavour. We usually begin to pick
our olives in the first or second week of November, that is, about two weeks
before St Catherine's day. These are all dates for our zone. In your area
picking could be some weeks earlier or even later. Friends who grow olives in
the Chianti area, for example, pick their olives two weeks before we do. The
same principle applies of a fixed date that only varies by a few days from year
to year.
The oil percentageWhen you are at the
frantoio or oil press waiting for your olives to be pressed all the
talk is about the oil percentage. Mine went 14%, what did you get? The
old-timers will reminisce about the harvests in their youth when they got 20%
and even more. They picked late – well into December and even January. Don't be
fooled. They may have got high percentages of oil but they did not get any more
oil as so many olives had fallen on the ground. If they picked them up the
quality would have been very poor indeed. The reason for the late picking was
the slow pressing. The frantoio could not handle the crop and the
olives were left to wait in the loft over the frantoio – sometimes for
weeks until they were mouldy. Given that choice, it was better to leave the
olives on the tree until time was available at the frantoio. Oil
percentages vary by as much as 5% from year to year. They are therefore useless
as an indication of maturity. You can delay harvest until you have achieved a
certain target oil percentage but you would be foolish to do so as many olives
may have fallen on the ground. You will have a lower yield in spite of the
higher oil percentage and the quality will also be poorer.
How to pickWe have now become such an
urban society that old rural skills are forgotten and despised. It is thought
that any fool can pick grapes or olives. Having picked many hundreds of tonnes
of grapes myself over many years, I know that this is not true. I continue to
marvel that amateur pickers can pick so few grapes and yet apparently look busy.
No doubt our local contadini think the same about my olive picking. The
most important thing is to have good olives to pick. Even a veteran Italian
picker will pick very little on unpruned trees where the few olives are
scattered all over the tree. One needs a net under the tree to catch the fruit.
In the past they used many types of material but I recommend a proper
olive-picking net made from knitted nylon that absorbs the energy of the olive
when it drops and reduces the amount of bouncing and rolling. On a really steep
slope you will still need to prop up the net. The nets come in all sizes. There
is no point in dragging a huge net around small trees, but on the other hand the
net must be big enough to catch all the olives. For mature trees a net of
between 6 and 8 metres square is used and for young trees one of 4 metres
square. The picking action is to pull your fingers down the twig and strip the
olives off without the leaves. One can also use a small rake. Most small
growers still pick by hand but machines are becoming more common. The only
machine worth considering for the small grower with a few dozen trees is the
electric one run from a car battery. I have no personal experience so I cannot
recommend them. When the olives have been picked on to the net you roll them
into a corner and pick out the twigs and leaves with olives attached. Do not
worry too much about the other leaves as they will be removed by the vacuum at
the frantoio. Where olives and leaves are still attached they will go
through the cleaner into the press; as it is better not to have leaves in the
oil, try to remove most of them at the picking stage. From the net they go into
crates. The crates have mesh sides to allow air through. Good air circulation
will reduce the chance of mould. Do not use solid-sided crates for this reason.
In the past the olives went into trays and were then transferred to sacks for
the journey to the frantoio but this involved pointless double
handling. The olives were often squashed in the sacks.
YieldsHow much do olives yield? How long
is a piece of string? The bottom of the scale is easy – nothing. Unfortunately
that is quite common. Our best trees yield 40 kg each and have on rare occasions
yielded more, even as much as 60 kg. We have seen irrigated olive trees in
Tunisia that yield 400 kg each. Over the whole of our grove we average 8 to 10
kg a tree. If the oil percentage is 14% this translates into a little more than
one litre of oil per tree.
To the frantoioFifteen years ago
when we first started to pick our olives all the local growers took their olives
to the frantoio at the end of the harvest. Naturally we did the same.
Since then we have come to realise that olives lose their flavour if they are
stored for two to three weeks. The rule of thumb I learnt from an expert at the
University of Perugia is that half the flavour is lost in a week and another
half of what is left in another week. Given that we pick for a couple of weeks,
that is more that we can afford to lose. We now try to take the olives to the
frantoio every three or four days. That means they are on average
stored for only two days. If we are picking good trees and are not interrupted
by rain, snow or fog we can pick 80 kg of olives a day on good trees, or about
300 kg in four days. This is about the minimum amount our frantoio will
take as a separate batch but the rule in each frantoio varies. You will
need to balance the amount needed for a batch against the time it takes and
whether you can work with a neighbour to form a bigger picking team. The olives
are pressed at the frantoio; and most presses are now able to keep each
batch separate so you take home your own oil and gloat over it. Quality is more
important for the small grower than for the commercial one. For the commercial
grower it is a question of costs and returns. For example, mechanical picking is
carried out later than hand picking because the fruit are too difficult to
detach by shaking. Late picking by machine may be cheap but the quality of the
oil is lower. For the small producer the objective is to produce the best
possible oil for your own use in sufficient quantity for yourself and some
friends. The quality is determined overall by the variety of olive tree, the
soil and the climate. The main ways of improving the flavour within these
constraints is to prune well, to pick early and to take your olives to the
frantoio every few days.
© Brian Chatterton
Kardamili in autumn and spring
by Chevrel TraherThe Mediterranean
Garden No. 47 January 2007
Near Canakkale, 9 km from Troy and across the Dardanelles from
Gallipoli, I run an olive grove of almost 6,000 trees on calcareous soils, which
forms part of a 150 Ha organic farm. The trees are mostly elderly, dating from
before the exchange of populations between Greece and Turkey in 1924, and have
survived since then on a regime of neglect and picking-by-beating. From time to
time some of them have been butchered in the name of rejuvenation (or
‘pruning’), and the general condition is poor. Yields are variable and currently
average around 10kg per tree, which, if you know your olives, you will realise
is pathetic (optimum yields should be approximately 45 kg per tree – more than
four times what we are getting).
The trees were last sprayed for olive fly
in August 2004. The decision to turn the land into an organic farm was taken in
November 2004, and the trees are therefore ‘in conversion to organic’ until the
end of the 2006 crop – after which they will be fully organic olives.
The great threat to olive crops being the ubiquitous olive fly,
the priority was to instigate a management programme which would deal with this
minute but hugely threatening pest. For control of the olive fly we chose to use
the Spanish olive fly trap. This consists of a clear plastic (PET) 1.5-litre
bottle, into which holes of 5mm diameter are drilled around the top part (we use
a soldering iron for this, with a metal template which fits around the top of
the bottle as a guide – and to prevent soldering ones’ fingers). These holes are
for the flies to come into the trap. The bottle is then filled with 1 litre of
ammonium bicarbonate solution, the cap screwed back on, and each tree gets a
trap. We hang them with a plastic-coated steel wire hooked around a convenient
branch in the shade. The flies simply adore the delicious scent of the solution
inside the bottles (it smells something like lavatory cleaner to us humans) and
fly from miles around in search of the source. Once inside the bottle, they
can’t find their way out again, because all of the attractant smells are inside
(and they are quite busy drowning in the solution).
As for results, this is a debatable issue. The olives picked in
2004 were riddled and pockmarked with olive fly damage – despite the fact that
they had in fact been sprayed! The olives picked in 2005, after a season with
fly traps, were 95% clean. I wonder if this was due to the success of the fly
traps, or whether it was the absence of pesticide which enabled the population
of olive fly predators (whatever creature eats olive flies) to multiply and hunt
them down. The fact is that although our traps caught many olive flies they also
trapped many other insects, some unidentified, but the overall numbers were
smaller than we expected. If anyone is interested in studying this subject with
us, he or she is most welcome.
With the fly issue more or less under control, the next critical
factor for olives is water. We don’t expect rain in Canakkale from April until
November or December. The critical issue for our particular trees is that the
last rain falls before the flowers can open, and the first rain in the autumn is
usually after (or during) harvest. The local people tell us categorically that
olives must not be watered. However, the truth is that though olive trees can
survive drought, they do like a drink now and again (don’t we all…). So we water
6000 trees during May and June. It takes 6 weeks with 4 ladies working 6 days a
week, and we give approximately 100 litres of water per tree, although larger
trees get more. In other words, 600+ tons of water. The critical factor about
watering in May is that if the trees are irrigated at the point of fruit-setting
(between flower and fruit), it encourages them to ‘set’ a larger quantity of
fruits per tree. In August, we repeat the whole process all over again. The
August-September watering encourages swelling of the fruit. Once again, the
timing is important: too early and the water is wasted; too late and the oil
content is lowered. With so many trees, and such a long period thus required for
each operation, some trees get watered too early and some rather late – but the
overall effect is to increase the total tonnage of fruit, which is
beneficial.
During 2005 none of the trees were pruned – the weather was bad,
and we were too busy doing other things… But in 2006 we have started a 5-year
programme for pruning the trees. This year, only ‘escapees’ were cut – two or
three branches per tree. These are the branches that are rising vertically
upwards and out of the tree canopy. They are too high up and difficult to pick,
and their removal allows more light penetration into the body of the tree. Four
boys with chainsaws and hand tools cut and collected approximately 12,000 olive
branches in 28 days, working flat out. The net result from this first phase of
the programme is to bring down the overall height of the canopies, which will
make picking that much easier. The second phase next year will be thinning the
bunches of new growth, singling out a few strong leaders for the future. During
the third year it will again be top-growth which will be reduced, and so on,
until we achieve happy and contented, conveniently shaped and sized olive trees.
Insaallah, as the locals say.
As for climate, in Canakkale we are borderline for
olive-growing. Once every 100 years or so, temperatures reach minus 12 degrees
Celsius. Once every 50 years or so, statistically, temperatures reach minus 6,
and temperatures of zero to minus 4 are expected routinely every two or three
years. The winter of 2003 (before we started) was a 100-year statistic. 185
trees were killed during that winter on this particular plot, all in one field
which is fairly flat and low-lying, and seems to have acted as a cold-sink. We
cleared the stumps to plant apples and other fruit trees. The winter of 2004 was
a 50-year statistic. Some trees lost the ends of their branches. The winter of
2005 was a 100-year statistic again (bring on global warming!) with a low one
Friday night of minus 12 degrees. We didn’t lose a single tree – twelve 20-ton
truck-loads of bark mulch, and any other mulching materials which could be
found, had been spread around as many trees as possible, as a thick mulch.
Perhaps it helped – who knows? Or perhaps the fact that we are not ploughing the
ground, but rather trying to encourage a natural meadow around and among the
trees, meant that the weed cover trapped sufficient snow to protect the trees
from freezing. Another opportunity for a research project, perhaps?
Previously, almost the only management technique applied to
these trees was routine ploughing of the entire soil area. In my view, this was
a diabolical approach – removing the vegetative ground cover, exposing the soil
to wind and water erosion, increasing the evaporation of soil moisture content,
depleting soil condition and resources, causing damage to the roots, and
destroying the natural habitat for any creature which might otherwise have taken
part in the local ecosystem. The stories in the village that there is treasure
buried on this land (by the Greeks) may also have something to do with this
practice!
The new approach of maintaining the vegetative groundcover as a
meadow system is radical indeed: no more digging for treasure, for one thing.
The idea of mulching each and every tree with a 10cm thickness of wood chips is
further evidence of our new-fangled madness – but add to that the hanging of
plastic bottles in the trees, watering twice a year and harvesting by hand (no
beating), and you begin to see how and why the villagers were convinced of my
complete craziness. This year, however, I noticed that in one field on the other
side of the valley the olive trees had been mulched with straw and compost – so
the crazy ideas are being watched and copied, by at least one person.
Harvesting is done entirely by hand. With 40 workers and
everyone else who could be mustered it took two months in 2005. A lot of
cajoling of the hired help, picnics in the fields, getting caught in the
rainstorm: it all adds up to the fact that we had a lot of fun amid the hard
physical labour. We plan to make the next harvest even more fun, and to invite
as many people as possible to come and join in the experience for a few days
each – having some ‘visitor’ pickers seems to encourage the hired help to work
more efficiently!
The management of all these issues ultimately leads to one
overall objective, that of increasing the overall yield. If we can raise the
average yield to 25 kg per tree within 3-5 years, this will be a success! At the
same time, regular and careful management to reduce the biennial periodicity of
fruiting will also benefit the project. In the future I also hope to find others
who will join the team here and take an active part in the analysis of the
efficacy of our efforts, in order to create effective guidelines for future
programmes.
© Chevrel Traher
Photographs by Davina Michaelides
Training and Pruning Olives
by Dr. Peter A. Roussos
Agricultural
University of Athens, Greece
From the Proceedings of the MGS Symposium: Dry
Gardening – Philosophy and Practice, Athens 2007
Olives and the environment
The olive
(Olea europaea L.) is one of the most characteristic tree
crops of the Mediterranean basin. During the summer, like all other
Mediterranean xerophytes, the olive is usually subjected to high solar radiation
and high air temperature along with high vapor pressure deficits and limited
availability of water. The olive is a sclerophyllous evergreen tree with a high
degree of drought tolerance, suitable to areas where little water is available.
The olive’s ability to acclimatize to water scarcity includes alterations at the
leaf level, associated with biochemical changes, morphological adaptation and
physiological changes.
Olive trees can grow also in nutrient-poor but
well-drained soils. The trees need full sunlight during summer and a slight
degree of chill during the winter for flower bud differentiation and fruit set.
Olive trees should not be cultivated in areas where the temperature often falls
below -5 oC, as they do not tolerate very low temperatures and get severely
damaged by winter or early spring frosts. Olive trees may also be damaged by hot
and dry winds, especially during the period of flowering and fruit set. Heavy
rains during this period also deplete pollen from the flowers and result in low
fruit set.
Planting layout
The planting scheme for
olive trees depends mainly on the cultivation system that will be applied to the
orchard (either intensive or non-intensive). For intensive cultivation fertile
soils and sufficient irrigation or rainfall are required, while these are not a
prerequisite for non-intensive cultivation systems. Olive trees have been
planted for years at intervals of approximately 10 m x 10 m or even more. This
planting distance leads to a limited number of trees per hectare (approx. 100
trees/ha). In areas which are characterized by a long period of drought such
spacing enables each tree to exploit all the available water (photo 1). However,
in areas where the climate is not so dry and the soil retains water these
planting distances are now considered too high.
In general there are two
main planting layouts:
The traditional one, where the trees are planted at intervals
of 7 x 7m, 6 x 8m, 8 x 8m or even 10 x 10 m (depending on the area)
Dense olive planting, where the trees are planted densely at 5
x 6 m or 6 x 6m.
For the past decade a new planting system is being tested in
olive cultivation. It is called the high-density orchard system and it uses
almost 1500-1800 trees per hectare (photo 2). The main objective of this system
is to reduce the cost of harvesting, which in traditional olive cultivation
amounts to about 40-50% of the total cost of producing olives.
Olive fertilization
Olive trees require
potassium, magnesium, nitrogen and boron.
Nitrogen is the element most
essential for both vegetative growth and the production of flowering and fruit
set. It may indirectly affect the alternate bearing phenomenon of olive trees.
Olives respond readily to nitrogen application when they are grown in low
fertility soils and when soil moisture is not a restrictive factor. Depending on
soil fertility and moisture, an average application of 500-1500 g of nitrogen
per tree is usually recommended for a bearing tree (1kg N= approximately 5kg
ammonium sulfate, 3kg ammonium nitrate, 4kg calcium nitrate or 2kg urea). The
timing of the nitrogen application should be related to the availability of
water, whether rainfall or applied by an irrigation system. Most fertilizers
containing nitrogen should be spread on the soil a few hours before rainfall or
irrigation, so that there is minimal or zero loss due to evaporation of the
nitrogen in the form of ammonia. The season of nitrogen application is strongly
related to flower induction and fruit set. Most of the quantity to be given
(2/3) is usually applied at the end of winter, before flower bud differentiation
and before the growth of new lateral shoots. The rest is applied during the
flowering period (from the pre-flowering stage till fruit set). At this time one
can apply nitrogen either directly to the soil (pre-flowering period) or through
foliar application (mainly with urea, pre-flowering and fruit set). In this way
the fruit set is significantly increased. The effectiveness of the nitrogen
fertilization programme can be assessed by checking the length of the new
growth, which should be sufficient when the appropriate amount of nitrogen has
been applied.
Phosphorus deficiencies are not so common in olive culture.
Phosphorus is usually applied every two to three years. The application of
phosphorus should be followed by its incorporation into the soil, so that the
mineral element can gradually reach the root zone (phosphorus is highly immobile
in the soil). It is considered necessary to give phosphorus when soils are acid
or characterized by high amounts of calcium carbonate.
Potassium is one of the main nutrients needed by the olive.
Large amounts of potassium are removed from the soil when the fruit is harvested
and by pruning, particularly in high-yield seasons. Regular potassium
fertilization is necessary to maximize both yield and quality. Potassium is
usually applied during the winter (after incorporation) in order gradually to
reach the rooting zone by the action of rain. In areas where the availability of
water does not pose a problem, potassium can be applied at the end of winter.
The fruit of the olive is highly demanding as it grows, which means that an
additional amount of potassium should be applied in the years of heavy yield
during the period of fruit growth, in other words in the middle of the summer.
This application is better given in the form of a foliar fertilizer, in order
for potassium to be readily absorbed and translocated to the parts (sink) of the
tree that need it.
Boron is also another major element required for olive culture.
Boron application as a foliar fertilizer usually gives better results when
applied during the pre-flowering stages. Thus the trees are sufficiently
supplied with boron, which plays a major role in pollen growth and thus fruit
set. Most growers combine a foliar fertilizer of boron with urea and some times
seaweed extracts during this period, in order to achieve the highest fruit
yields.
Magnesium is also another major element needed by olives. It is
a major constituent of the chlorophyll molecule. This means that it plays a
significant role in photosynthesis. Magnesium is usually given only after a
deficiency has been detected. Nevertheless, most fertilizers contain a
significant amount of magnesium, so that it is applied in sufficient quantities
along with the other major elements (nitrogen-phosphorus-potassium: a full
strength fertilizer of the type 21-21-21-2 w/w means that it contains 21% of
nitrogen, phosphorus and potassium and 2% w/w of magnesium).
The best way to evaluate the nutrition status of the olive tree
– as of any plant – is to carry out a soil analysis along with a plant tissue
analysis (usually leaves are used). These analyses will give significant data on
the status of both soil and plant, indicating the appropriate fertilization
programme to be applied.
Pruning
Pruning is rightly considered by
many agronomists to be the major cultural practice in an orchard. By pruning,
the grower adjusts the tree to the specific climatic and soil conditions of the
area and increases the productivity of the orchard. The main aims of pruning are
summarized below:
To give to the tree the best shape under the particular soil
and climate conditions
To balance the vegetation with the fruit yield
To minimize the non-bearing period
To prolong the productivity of the orchard
To delay senescence
There are three main types of pruning:
pruning during the early stages of the tree’s growth
pruning for fruiting
rejuvenation pruning
1. Pruning during the early stages of the tree’s
growth
The aim of this type of pruning is to develop a tree shape
during the first years after planting that will facilitate all cultural
practices (spraying, soil cultivation, irrigation, harvesting etc) and will
enable the tree to best exploit the sunlight and rainfall occurring in the area
of cultivation.
The most common shape for the olive tree is the “cup-shaped”
tree or “free-cup”. To form this shape the newly planted one-year old trees are
cut back to a height of approximately 60-80 cm above soil level. The main aim of
such a practice is to force 2-4 side branches to develop around the axis of the
tree, at a distance of 30-40cm from each other and at a height of approximately
40 (the first) to 80 cm from the ground. These branches should in future
comprise the main branches (primary limbs) of the tree. On these branches new
side shoots will be encouraged by cutting the old branches to a length of
approximately 50cm, thus removing the so-called shoot tip dominance and making
the lower buds sprout.
There are also many other tree shapes that are used around the
world, some of which are shown below.
The two-branch shape, which is common in Andalucia, Spain, for
table olive varieties.
The candlestick shape used in Tunisia.
The double or triple trunk shape used in Seville.
The multi-conical shape, in which every branch has the shape of
a cone, found in some regions in Italy.
The spherical cup shape seen in France, Italy and Greece.
The spherical shape, which is not so common because it does not
give ample light to the whole tree.
The short cylindrical shape.
The non-trunk shape seen in Tunisia.
The free palmate. This shape presents some difficulties and is
not widely used, at least for olive oil producing varieties.
Various olive tree shapes.
2. Pruning for fruiting
Olive trees produce
fruit on the previous year’s branches. This means that in order for us to have
fruit every year we must ensure adequate vegetative growth every year. Very
vigorous shoots are not productive, as they are mostly full of vegetative buds.
The aim of pruning is thus to induce branches that will bear fruit by exposing
them to the light and maintaining a vigorous and active fruiting zone.
The
olive tree produces fruit mainly at the periphery and top of the canopy. This is
because these parts of the tree are fully exposed to sunlight and become
fertile. Based on this fact and on the aims analysed above, pruning for fruiting
should consist of the removal of any part that shades other younger parts of the
tree (photo 5). In this photo we can see that the branch which now has fruit on
it will be cut down during the following year in order for the upper branch to
bear fruit (due to the favourable lighting conditions), which would eventually
lie over the older branch and shade it, thus making it non-fruiting. In this way
the branch is not led away from the central axis of the tree, as can be seen in
photo 6.
When a thick branch is to be cut off we must take great care to
avoid tearing the bark of the remaining branch. This is usually done by making a
total of three cuts, as it is clearly shown in Figure 1. The first cut is made
from the lower side of the branch to the middle of it, some centimetres away
from the point where we want to cut the branch. The second cut is made a few
centimetres away from the first cut and usually before the completion of this
cut; due to the weight of the branch, it will fall, tearing the bark of the
remaining branch to the point where the first cut was made. We can then easily
cut off the small remaining part, to the point desired.
Scheme of the pruning of fruiting branches over a two-year
period.
3. Rejuvenation pruning
The main
characteristic of the olive tree is its longevity, resulting from its ability to
produce new shoots from nearly every part of the wood, thus making it possible
to renovate senescent trees or those that have been damaged by frost or fire.
This type of pruning is consists of cutting the tree at the main branches or
even at its trunk. The most significant practice, however, is to return during
the next months and remove by hand (when they are still young) the shoots that
will be of no use to us. We should not wait until the following year to give the
tree the shape we desire (pruning for shaping the tree), as we would very likely
have wasted almost an entire year before the beginning of fruit production. The
new tree enters its fruiting period after 3-5 years, depending on the cultural
practices used.
After any pruning or cutting it is advisable to cover the wounds
with wound-sealing pastes and to spray the trees with a copper-based fungicide,
in order to prevent the tree from developing bacterial or fungal infections. The
pruning of olive trees can be done during the period between autumn and winter.
It is generally performed after the harvest, but we should wait until the period
of heavy rains and frost has passed in order to prevent infections. We should
never prune on a rainy day, as this will probably spread bacteria to the cut
surfaces or to internal wounds invisible to the naked eye, resulting in
bacterial canker of the living tree (for those varieties susceptible to
bacterial canker).
Irrigation and weed control
Irrigation and
weed control of olives grown in gardens is usually a simple practice and there
is nothing special to be noted. Nevertheless, we should know that the critical
phases for water stress in the olive tree are principally the periods before and
after flowering (during fruit set), when drought can result in a significant
reduction in the flowering and thus the fruit set, leading to low
production.
© Petros Roussos
