Growing olives trees for fruit production in southeast Queensland can be a challenge but with a good understanding of the trees cultural requirements and careful variety selection quality yields can be obtained.
Throughout the world, the major olive growing regions are almost exclusively found in Mediterranean type climates that are characterised by a winter rainfall pattern, mild winter temperatures and hot dry summers. A Mediterranean climate is one that resembles those of the lands bordering the Mediterranean Sea. These climates generally occur on the western coasts of continental landmasses, roughly between the latitudes of 30° and 45° north and south of the equator.
In southeast Queensland we have a subtropical climate of warm winters with a summer rainfall pattern and high summer humidity. Although distinctly different to the Mediterranean climatic, as long as some basic requirements are met such as good soil drainage and adequate pest management, olive trees will generally grow well in region. Fruit yield, however, can be inconsistent unless a suitable variety is selected and steps are taken to manage the flowering and fruit set processes.
Some winter chilling is required for flower initiation. In general, growing many of the traditional olive varieties in areas that rarely frost during winter can be a fruitless exercise as there may not be enough winter chilling for the flower initiation processes to take place. Some of the more recently introduced varieties into Australia, however, are more adaptable to warmer climates and will fruit well under the prevailing conditions.
Varieties which have shown to be the more consistent in their bearing habits in warmer climates include: Arbequina, Manzanillo Arecuzzo and Koroneiki. Of these, Arbequina would be the standout as the most reliable bearer in warm climates. It is self-pollinating and bears when it is very young. In a warm winter variety trial in southeast QLD, Arbequina produced an remarkable average yield of 18kg per tree after 3 yrs.
We suggest that growers who intend to plant olives in a warm climate, outside of the traditional climatic zones should regard the initial planting as a trial and not a commercial venture until varietal performance is proven.
Although most olive varieties are self-fertile to some extent, research has shown that cross-pollination improves the fruit set of most varieties especially when the environment conditions are not optimal. Generally having two or three different varieties growing in close proximity (30m) will facilitate adequate cross-pollination. Arbequina, Arecuzzo and Manzanillo are some of the main varieties used for cross-pollination in QLD. If a tree flowers well in the spring and does not set any fruit it may be good indication that cross-pollination is required.
Soil Moisture and Irrigation
Adequate soil moisture throughout winter and spring is essential to ensure good flowering and fruit set. In olive trees, the process of flower initiation and development starts in late autumn and continues through the winter. Under winter drought conditions, this process is disrupted, resulting in either poor flowering or an excess of malfunctioning flowers that prematurely drop without setting fruit.
If rainfall is inadequate, it critical that supplementary irrigation is applied throughout winter and spring. Conserving soil moisture by spreading mulch and managing grass and weeds around the trees is also important. Young olives trees are poor competitors. Weeds and grass in the root zone of the tree will stunt growth and out-compete the tree for water and nutrients.
Adequate levels of nutrients especially nitrogen and boron are required for optimal flowering and fruit set. A leaf analysis taken in mid summer will give a good indication of the trees nutritional status and fertiliser requirements. Generally olives require either manure or other fertiliser on an annual basis for good fruit set. Splitting fertiliser applications throughout spring (60%) summer (30%) and autumn (10%) is recommended for granular NPK fertilisers. Manure is best applied as mulch once a year in late summer or autumn. The benefits of applying fertiliser will be limited unless there is adequate soil moisture for nutrient uptake by the tree.
Applying boron and calcium to the trees as a foliar spray before bud burst will help to meets the trees requirements of these nutrients and can improve pollination and fruit set.
Keep in mind that although the olive is a hardy and adaptable tree with the ability to withstand harsh summers, severe drought and poor soils, without adequate cultural care tree performance and fruit yield will be poor. Neglected trees, however, can be rejuvenated and brought into production with severe pruning and ongoing management practices.