Although the hardy, evergreen olive tree can survive for centuries with no attention, it will only produce economically viable crops if given the necessary care. Here’s some background and the basics.
Table olives and olive oil are, like wine, associated with an element of mystique, yet the successful cultivation of this crop requires sufficient know-how. Unlike other fruit, olives cannot be eaten fresh off the tree – a characteristic that has both advantages and disadvantages.
Table olives are processed by various methods before they are edible, and the most popular recipes are those that include specific microbial fermentation. Olive oil, on the other hand, is at its best when freshly extracted at ambient temperature simply by mechanical means.
The olive is traditionally grown in areas that have a climate similar to the Mediterranean type, to which it is ideally adapted. Such regions are typified by relatively cool winters where frost seldom occurs, hot dry summers and an average annual rainfall of around 700 mm.
- Olive trees will also thrive under irrigation in drier areas.
- In summer-rainfall regions experiencing high humidity and temperatures, pests and diseases are a problem.
- The olive requires sufficient winter chilling to enter rest so that flower development is initiated, otherwise the tree remains vegetative.
- Maximum day temperatures in June and July should not exceed 21°C, otherwise no fruit will be borne.
- On the other hand, frost can seriously damage olive trees, especially young trees, young shoots and inflorescences, resulting in serious losses.
- Entire trees can die when exposed to temperatures below -7°C, especially if the fall in temperature is sudden.
- Rainfall or fog during blossoming will affect pollination negatively.
- Temperatures exceeding 30°C around flowering time will result in poor fruit set.
- Olive trees are less sensitive to wind damage than other types of fruit.
- Olive trees require well-drained, well-aerated soil that has been prepared according to recommended guidelines to a depth of at least 80 cm before planting.
- Production on shallower soils will be disappointing, while trees planted in wet or waterlogged soils are susceptible to asphyxia and diseases.
- Very sandy soils have poor water-retention capacity and will require intensive management in terms of irrigation and nutrition.
- Heavy clay soils (above 35% clay) are unsuitable, whereas stony soils, especially with high gravel content, are ideal.
- Soil pH (measured in KCl) should be between 5.5 and 6.5.
- Irrigation is usually by means of drippers or micro-sprinklers, and is a prerequisite for the regular production of high-quality fruit.
The choice of which cultivars to plant is determined by the following:
- The market demand for the specific product (for example olive oil or table olives), the type of processed products required (for example black or green table olives), and the suitability of the cultivar to the specific processing recipe.
- The adaptability of the cultivar to a specific region, especially regarding production, resistance to pests, diseases and possible frost.
- The cross-pollination requirements of the cultivars, which can be quite specific.
- The ripening period and harvest season of the cultivars relative to other cultivars, other fruit kinds (where relevant) and other management practices.
- The availability of planting material.
- It is recommended that olive trees be ordered from registered nurseries in the year prior to planting.
- Trees are usually propagated by nurseries by means of cuttings (on own roots) and supplied in planting bags.
- Those that are difficult to root from cuttings are sometimes grafted onto rootstocks.
- There is very little information available locally on the performance of specific rootstocks, but clonally rootstocks is preferred above seedlings because of the variability of the latter.
- Trees should have healthy appearance, be 12 to 18 months old, at least 50 cm in height, and should be planted in late winter or early spring in order to be successfully established in the orchard.
- Planting distances will depend on circumstances, but traditionally trees are spaced 2 m to 4 m apart in the row, and rows 4 m to 7 m apart.
- An alley width of 2 m is sufficient for normal orchard traffic.
- For mechanical harvesting by trunk shakers, alley width has to accommodate the efficient operation of such machines.
Light can only penetrate the canopy to a depth of 75 cm, therefore reduced tree dimensions will be more efficient, in terms of land utilisation, spray coverage, ease of harvest and improved, more regular fruit production and fruit quality, but will require more intensive management inputs.
In the super high-density system, which is a specialised, intensive method of training central leader trees of specific cultivars on trellis for harvesting by straddle harvesting machines, trees can be planted as close as 3.5 m x 1.2 m.
HARVESTING AND FRUIT HANDLING
Table olives are picked separately and carefully by hand and placed in picking bags or buckets, while oil olives are usually stripped off the trees onto nets placed on the ground. Harvest date depends on the cultivar and the purpose for which the fruit is intended.
Fruits intended for green processing are picked at the stage when they have turned from bright green to yellow green, and the first fruit shows a light pink or purple blush. Only fruits of the required size are harvested while the rest is left for later picking.
The fruit intended for processing as ripe black table olives are picked when they have turned completely black, but before they become overripe and soften. Oil olives are harvested when most of the fruit on a specific tree is ripe enough, and then the entire crop on that tree is picked at once.
For machine harvesting, cultivars are picked according to their optimum ripeness, where a portion of the fruit is at the quarter-ripe stage, most of the fruit is at the half-ripe stage and a portion is at the three quarter-ripe stage.
The oil content rises initially with colouring and ripening, and then remains relatively constant. Greenish fruit contributes to fresh, greenish fruit flavours and higher levels of beneficial antioxidants in olive oil. Delay in harvest will result in lowered oil quality.
Growing olives is a long-term venture, with the return on investment gradually increasing as trees mature. New production systems have been developed to allow a quicker return on investment.
- Mission is widely adaptable and is especially suited to black table-olive production, as well as for olive oil.
- Kalamata is ideal as a black table olive. Trees are less adaptable than the Mission cultivar, and difficult to propagate.
- Manzanilla is especially suited to green table-olive production, has low oil content and softens on ripening.
- Barouni is only suited to green “Queen” table-olive production because of its large fruit size and low oil content.
- Frantoio is suited to the production of high-quality olive oil and as a cross-pollinator for the other cultivars.
- Maurino is suited to the production of high-quality olive oil, for both intensive and conventional growing systems.
Also read: Fruit farming is a long-term investment
- This article was written by Carlo Costa and first appeared in Farming SA.