Olives are mostly self-pollinating, hardy, evergreen trees 7 -12m tall, with small leathery leaves in an oblong-lanceolate shape, with a silvery-grey underside. They live to a great age (1500 years). They are vigorous growers, adding about 45cm per year. Different varieties are planted for particular end uses, which include pickling, oil manufacture and stuffing.
Pickling is required before the whole fruit can be eaten, to remove a bitter taste. This is achieved with a weak alkaline solution (common salt) or can be quickly accomplished with a stronger alkaline solution (caustic soda). The caustic soda method requires very efficient flushing, first with salty and then fresh water, to remove caustic. The wood of olive trees is excellent cabinet timber and is used for carving.
Olives can be grown on all soil types except in boggy conditions. They do not like wet feet. Olives are cold tolerant but do best in warm areas.
Olives in plantations have been traditionally planted 10-12 m apart. They are also planted in windbreaks at 4-5m spacings, or 3m for a very quick windbreak effect. They can also be close planted at 1 metre spacings, and in this form they produce a hedge with thick shade. Modern plantation techniques favour closer planting (10m x 5m) for maximum yield to age twelve. At twelve years every alternate tree would be removed, however this practice requires extreme measures to prevent regrowth from the trunk -either poisoning or stump removal.
Propogation of olives is usually done by stem cuttings and pieces of old trunk, 5-7 cm in diameter and 30-60 cm long, or by rooted tip cuttings, using hormone powder. Seeds are slow germinating and require scarification. Budded trees are no longer used for commercial planting.
Trees may be close planted in a nursery, from cuttings, and dug up for replanting in the orchard. This will save space in the plantation and allow exploitation of the grazing capacity of land for an extra 2-3 years.
Olives were much planted until the early 1920's, largely from un-named varieties, as they propagate readily. Olives were then ignored for a long time and many plantations were removed. This is hard to explain as the temperate climate of south-eastern Australia is ideal for olive production. The Two Wells area and the McLaren Vale area in particular have a reputation for world-class oil production from olives. Some experimentation with varieties has started again, but proceeds at a slow pace.
Verdale is healthy and prolific in the Riverland of S.A.
Manzanillo is an even-ripening variety with good flesh to pit ratio, green or black production, reasonable oil content (multi-purpose tree), reliable cropping (best with a cross pollinator) and requires some winter chilling.
Another variety once widely planted on the Adelaide Plains was Queen, also known as Sevillano, a large fruit grown for green pickling, its fruit is larger than a Verdale, the skin tougher and the pit large
A 1955 catalog from the Beaumont Olive Plantation shows other varieties available as "Hardy Mammouth", "Ascolana", "Salome", "Oji Blanco" (also Hojiblanca), "Cucco", "Borreigola", and "Morhiso".
Frontiniana is a Sicilian variety, a prolific bearer of high oil fruit for pressing, which was widely planted for windbreaks and poultry or stock food.
Other varieties are Nicoise, Lugano and Kalamata (black pickling), Picholine (green pickling), Royal, Gordal and Arbequina.
Black scale is perhaps the worst pest. It can be treated with summer spraying oils in mid-December when the crawlers are moving. Curculio beetle can also cause some problems, especially in young trees.
General cultural information
Olives produce blossom in November. For green olives the fruit is picked in March and April. Black olives can be picked from the same tree by knocking in may. Oil Olives may be left to ripen in winter.
Some pruning is required to remove "spent" brush (especially around the tree skirt) each year. Commercial production often involves chemical thinning to avoid a biannual fruiting habit.
In California 80 year old plantations are in full production and in Spain 200 year old plantations are relatively common. Fruit quality in Australia is very high but the productive life of plantations under irrigation, or unirrigated, is unknown in Australia.
Commercial olive culture
The largest olive orchard in Australia is "Oliveholme", at Robinvale. It is a 256 hectare property, producing olives for the table as the main enterprise. Two large orchards remain in the Riverland, growing olives for the table. There were large oil plantations in South Australia, many planted by famous pioneer families such as Cleland, Crompton and Chaffey, but few of these run as commercial enterprises today, and most of the trees have been felled. A few remaining properties include Francescas at Clare and Coriole at McLaren Vale. They produce high quality oil that commands a very good price. Other notable plantations are around the Grampian Mountains, Horsham and Bordertown.
For the past 50 years few olives have been planted because it was not possible to compete with the price of low quality bulk oils from the Mediteranean region (chiefly Spain). However the situation may have changed due to broadening of Australian culinary tastes and the development of a gourmet market.
Harvesting is by knocking with sticks onto sheets spread upon the ground, with care not to damage next years fruiting wood by bashing too hard. Some mechanical harvesting tools are now available, and they can significantly reduce the labour component of harvesting.
The following estimates are from a 1955 catalogue of the Beaumont Plantation:
Year 5 60lb per tree (27.21Kg)
Year10 240lbs (108Kg)
Year 15 4cwt (203.2Kg)
The trees at Oliveholme are irrigated with two, 2-litre per hour drippers per tree. Olives will grow without irrigation, witness wild olive trees in the Mitcham Hills area or at Terangie (Adelaide Hills), or in windbreaks around the Willunga area (including Colville Road). However irrigation will improve tree health and production and should be considered essential for young trees. In a situation with very limited water, trees could be drip fed for the first three years and then removed from irrigation and the same lines used to replant new rows. This technique could be used to plant one row per year, reusing the first drip-line in year four, thereby staging the investment in tree stock and making best use of limited water supply.
The Complete Book of Fruit Leslie Johns & Violet Stevenson, Angus & Robertson
The Essential Olive Oil Companion Anne Dolamore, Macmillan