Climatic & Soil Requirements
The olive is traditionally grown in areas having a Mediterranean type of climate 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 800 mm. The olive will also thrive under irrigation in drier areas.
In summer rainfall regions experiencing high humidity and temperatures, pests and diseases are problematical. The olive requires sufficient winter chilling to enter rest and so initiate flower development 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 of minus 7°C. Olive trees are less sensitive to wind damage than other types of fruit.
The olive requires a well drained, well aerated soil which 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 on wet or waterlogged soils are susceptible to asphyxia and root 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 above 5.5, and preferably near 6.5. Irrigation usually by means of drippers or microsprinklers is a prerequisite for the regular production of high quality fruit.
The choice of which varieties (or more correctly 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 (e.g. black or green table olives), and the suitability of the cultivar to these specific products;
- the adaptibility of the cultivar to a specific region, especially regarding production, resistance to pests diseases and possible frost;
- the cross pollination requirements of the cultivars;
- 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.
The following range of cultivars have been shown by trial results as well as experience by the industry to be the best currently available.
The most popularly planted at the moment in South Africa and is widely adaptable. It is especially suited to black table olive production as well as for olive oil.
Ideal as a black table olive, with a lower oil content than Mission. The tree is less adaptable than Mission and is difficult to propagate.
This cultivar is especially suited to green table olive production , has a low oil content and softens on ripening.
Only suited to green “Queen” table olive production because of its large fruit size and low oil content.
Suited to the production of high quality olive oil and as a cross pollinator for the other cultivars.
It is recommended that olive trees be ordered in the year prior to planting from registered nurseries who are listed with SA Olive. Trees are usually propagated by means of cuttings (on own roots) by nurseries and supplied in planting bags. Those which 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 clonal rootstocks are preferred above seedlings because of the variability of the latter. Trees should have a healthy appearance, be about 18 months old, at least 0,5 metres 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 4 to 5 metres apart in the row and rows are spaced 6 to 7 metres apart. An alley width of two metres is sufficient for normal orchard traffic. If mechanical harvesting becomes an option, alley width has to accomodate the efficient operation of such machines. Under intensive management trees can be spaced closer and their height reduced accordingly.
In most cases thorough soil preparation is necessary before planting. This entails deep ripping and/or delving criss-cross over the entire area while simultaneously incorporating and mixing the necessary ameliorants such as lime and phosphates according to soil analyses. On a smaller scale, individual planting holes of one cubic metre can be dug and the soil thoroughly mixed with the predetermined amount of rock phosphate, lime and organic material. Consult experts on the soil preparation practice recommended for your specific soil conditions.
Trees are planted as follows: a hole of about a spade width and depth is dug, the planting bag is slit open around the base, which is removed as the tree is placed in the hole, at a level slightly deeper than it was in the bag. Normally the roots are left undisturbed, but if they are growing around in a circle, they should be loosened lightly. The rest of the bag is then removed and the hole filled with soil which is firmed down around the tree. Trees are watered where necessary. Fertilizers are not to be placed in the hole at planting since direct contact can burn the roots.
The tree trunk is protected from sunburn, herbicides and rodents by means of a carton-foil tube. Trees are staked to promote rapid upright growth, and to protect against wind damage. Make use of a sturdy bamboo or wooden stake to which the main leader is loosely tied with a twine. The twine should not be tight around the stem, otherwise the tree will be girdled and die, nor must the tree be right against the post, otherwise no branch development occurs on that side. Use twine that can decompose before it does damage to the growing stem (not polypropylene).
According to Act 36 of 1947 olive producers may only use chemicals which are registered for use on olives in South Africa. Please refer to this document for the latest list of registered chemicals.
Nitrogen is utilised throughout the growing season, and is to be applied monthly in spring and summer to young trees in the form of Ammonium Sulphate or “LAN”. It is recommended that nitrogen is applied regularly and in smaller doses to prevent excessive vegetative growth caused by single large applications.
Be especially careful of injudicious nitrogen applications in the summer months. Potassium (e.g. potassium sulphate) is applied in spring and autumn. Under local conditions replenishment of B and Zn are especially important in early spring.
Other elements are applied according to rates determined by means of leaf and soil analysis and adjusted according to expected crop, otherwise, imbalances can occur. Maintaining soil acidity at the right pH level (in the region of 6.5) is critical for facilitating the optimal uptake of other nutrients. Soil pH is determined during soil analysis (which should preferably be done on an annual basis) and rectified accordingly by lime application.
Chemical weed killers have to be used with care since the long-term effects on tree performance and the environment have not been determined. In an organic farming system, a relatively thick mulch layer of high lignin material in the tree row helps suppress weed growth and stimulates beneficial fine root development.
Lateral branching is encouraged over the entire length of the leader from a height of about 40 cm upwards, with stronger development at the base to form a conical shaped tree. Lateral branches should have a diameter of less than a third of that of the main leader and are kept at a flattish angle while all upright growth on the laterals is regularly removed.
The main pests which occur on olives in South Africa are:
- the yellow and black striped olive beetle, with its bright yellow larvae which eats and tunnels into leaves especially on young trees, destroying new growth.
- the olive lace bug or “tingid” which sucks out the sap of leaves, especially where growth is dense, and so causes tiny yellow dots on the leaves which later become completely chlorotic and die.
- the olive fly, which stings the fruit and lays its eggs which then hatch and destroy the fruit as the larvae burrow through the flesh.
Under dusty conditions, infestation by various scale insects can be damaging. Insects such as psylla only become serious pests when the ecological balance is disturbed through injudicious pesticide use. Effective control of most of these pests is available, but one should always strive to allow biological control to take place.
The main fungal diseases include:
- anthracnose (Colletotrichum), which causes fruit spoilage and cankers on shoots;
- peacock spot (Spiloceae) which causes sooty spots and yellowing of leaves, later resulting in leaf drop and death of shoots;
- various soilborne diseases (Phytophthora, Verticillium etc.) which cause damage to the roots and can lead to the death of trees
These diseases are controlled by integrated management practices.
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 and normally stretches from February to July in the Western Cape.
Fruit which is intended for green processing is picked at the stage when they have turned from bright green to yellow-green and the first fruit show a light pink or purple blush. Only that fruit which is of the required size is harvested while the rest are left for later picking.
Those 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 the tree is ripe enough and then the entire tree is picked. The oil content rises initially with colouring and ripening, then remains relatively constant, but a delay in harvest will result in lowered oil quality.