WAIMEA OLIVES
Growing Information
The olive (Olea europaea), traditionally the symbol of peace and tranquillity, is a long-lived, evergreen tree providing shade and food to those who nurture it. It is a member of the Oleaceae or ash family and thrives in warm temperate to sub-tropical regions similar to the Mediterranean basin from which it is native. Olive trees are generally easy care plants. Trees live for many hundreds of years and there are profitable commercial plantings in Spain that are over 200 years old.
CLIMATE
While the olive tree has a wide range of adaptability there are cultivars much better suited to some conditions than others. Without a good winter chilling many varieties fail to initiate flower buds. However some cultivars, such as Azapa, Koroneiki and Chemlali bloom and fruit with very little winter chilling, so are suited to warmer areas.
In the colder regions of New Zealand where winters also start early, the fruit may fail to fully ripen especially with later maturing selections. Variety selection in such areas is especially critical. Young olives trees can be injured by cold winds and hard or unseasonal frosts. Only a few selections as mature trees can withstand temperatures below -10 degrees without damage. The hardiest varieties include Leccino, Picual, Picholine, Frantoio, Sourani, Moraiolo and Pendolino.
SOILS
Olive trees will grow on poor soils but deep reasonably fertile soils produce the best quality fruit. Research suggests that elements such as nitrogen, potassium and boron are most important for commercial olives so a soil test 6 months prior to planting is recommended when a grove is been established. They prefer soils that are in the slightly acid to neutral range (pH 6-7 optimum). Olives detest wet feet so soils must be free draining.
PLANTING
In New Zealand olives have been mainly planted 3m - 6m apart and 5m - 6m between rows to allow for machinery access in the future. Spacing does depend on factors such as variety vigour, the amount of pruning intended and both the training and picking methods to be employed. The new dwarf cultivar FS17 is recommended to be planted at 2m by 4m spacing or even closer on infertile soils (a separate booklet is available from Waimea Nurseries on FS17 and high density plantings of olives).
Planting time will depend on a number of factors. As another general rule autumn planting is recommended in areas not prone to harsh or very wet winters. Spring planting is best in areas where winters can be severe. Other factors to take into consideration to help decide best planting times include age of stock, availability of irrigation and seasonality of strong, potentially damaging winds.
The NZ Olive Association have found that after-care is the greatest stumbling block to olive tree establishment. Weed control, attention to irrigation needs, adequate staking, pest and disease control must be attended to.
IRRIGATION
The olive is considered a drought-resistant species because it thrives in areas where water stress is frequent. However irrigation is likely to be needed to maximise growth and eliminate stress during flowering, fruit setting and as the fruit increases in size.
Over watering can cause health problems for olive trees. Research is also showing that over irrigation in autumn can delay harvesting while doing nothing for increasing fruit size or quality (see notes on Harvesting).
PRUNING
There is still much debate on how best to train and prune your olive trees. Different cultivars have different growth habits and so training techniques will vary. Trees should be developed into an open vase shape with the typically low developing branches radiating out in an even pattern. Once trained, minimal pruning is required to maintain a mature specimen, often requiring only minor branch thinning and dead wooding. All pruning is best done either in late winter/early spring or at bloom time.
HARVESTING
Like all fruit, olives perform best when picked at the right time for the purpose. As different varieties of olives perform best when pickled at different maturities you need to either experiment or research best picking times for your table selections. Oil olives should be harvested as soon as possible after they have become fully ripe. The NZ Olive Association suggests that this is when half the olives have turned black. As olives ripen, the quality of the oil within changes. Commercial growers maybe best advised to use lab testing for oil and moisture content to judge when exactly to harvest.
PICKLING
Whether green or black, perfect unbruised olives are best for pickling. Keep them cool. These can be prepared in plain brine or oil or combined with virtually any herb you care to name. Processes and recipes abound and each grower will hopefully develop their own unique blend that best works for them.
POLLINATION
Pollination requirements do vary between the different Olive varieties. While several of these varieties can be classified as self fertile, the majority of olive trees greatly benefit from cross-pollination so groves should have a mix of cultivars inter-planted for this purpose. Olives are wind pollinated. As such Olive pollination can be affected by climatic factors such as heavy rains and strong or no wind during the flowering period.
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