The good oil

This is not Sydney Royal Botanic Gardens' olive plantation. We have ten trees on a lawn overlooking the Herb Garden. Planted in 1995, they began to fruit a couple of years ago.

There are 33 species of Olea, including one native Australian species Olea paniculata, and hundreds of European Olive cultivars. Although European Olive (Olea europeaea subspecies europea) has become a weed in abandoned orchards in places such as the Adelaide region, it is the African Olive (Olea europaea subspecies cuspidata) that causes havoc in the native bush around Sydney.

African Olive was introduced into Australia for ornamental purposes, as a garden specimen or hedge plant rather than as a horticultural crop (although it was trialled, unsuccessfully, as rootstock for European Olive). It’s a declared noxious weed in New South Wales and South Australia. You can pick it from the European Olive by the hooked leaf tips and the green or brownish (rather than whitish) under surface of the leaves.

In a very Ark like manner (although I'm aware from QI that not everything in the fabled Ark was paired), our olive grove has two of a few of the more interesting, and relatively environmentally safe, cultivars of Olea europea.

There is the ‘Manzanillo’, a classical Spanish olive, and a heavy bearer of fruit that travels well (i.e. it is resistant to bruising). This one is good for oil, as well as green and black pickling.

The ‘Mission’, grown commonly at old missions in California, is more cold resistant but has smaller fruit on a taller tree – and is therefore difficult to harvest – plus a susceptibility to a fungal disease called Peacock Spot. We’ll keep this one regularly pruned to keep the tree open and well ventilated.

‘Sevillano’ is often sold as the Queen Olive. It produces loads of large fruit, but the oil content is low and the flesh considered poor quality. You’ll find it in Sicilian style salt-brine cured olives and in many cans of olives.

Uc13a6 hasn’t yet been given a romantic name. It’s a selection by the University of California from ‘Tafahi’, an Egyptian cultivar, and should be well suited to hot climates. The profusely produced fruits are large, round and fleshy.

Our fifth and final cultivar is the mainstay of the olive industry in Australia. ‘Verdale’ was originally bred in France but I think we have the South Australian Verdale. It produces medium-sized, good quality fruit, and good yields, and the low spreading tree is easy to pick from.

There are lots we don’t grow of course, including my favourite eating olive, the Kalamata, which can be a little temperamental to grow in the Australia.

Watch out though, olive oil has some competitors. In 2007 there was a report of a new ‘wonder peanut’ being harvested in the USA which reportedly not only provided greater health benefits, it gave growers better yields and a longer product shelf life. But did it taste as good as olive oil? We need to know the answer to that question before we attempt a peanut farm at the Royal Botanic Gardens.

Image: Olive plantations not in Sydney's Royal Botanic Gardens, but in Avignon, in southern France. *This posting is from the Radio Archives (May 2008).