THE OLIVE
SCIENTIFIC NAME: Olea europaea
FAMILY: Oleaceae
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.
DATE: May 1997
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