Olive Tree

Olives: Ongoing Care & Maintenance

Olive trees require minimal ongoing care and maintenance.

Any suckers that have formed around the base of the tree can be removed and mulch should be topped up as required.

As they are fairly drought tolerant, once established they will only need regular watering if grown in a container. In the ground, they need no water unless there is a prolonged dry period.

As they are generally hardy, container-grown trees will only need to be protected or taken inside if there is a risk of hard or prolonged frost.

Olive trees do not tend to have issues with pests or diseases but it is good practice to monitor your plants regularly just in case. The most common pests are scale insects and the Olive fruit fly.

There are some known pests of the Olive Tree. Scale insects are rare but can occur, and Peacock spot (Spilocaea oleagina), is a fungus that causes lesions on the foliage and the fruit. It can be treated in Winter after the fruit is harvested, by spraying copper oxychloride to destroy the fungal spores. The other problem with Olive Trees is birds who start picking off the fruit as soon as the olives start ripening.

The only pruning that is advised is light corrective pruning – the removal of any branches that are dead, diseased, damaged or crossing. This should not be needed during the first 2-3 years of growth but can be carried out at any time of year as long as there is no risk of frost or a long dry period. If pruning a tree that is being grown for fruit, the best time to prune is directly after harvest.

Olives: Propagation

The Olive tree can be propagated by seed and cutting.

Seed should be collected and sown when fresh in autumn, into a pot of well-drained seed-sowing compost. Place in a bright position away from direct sunlight and keep moist. Seedlings will emerge in spring and can be potted once the first true leaves have appeared.

Semi-ripe cuttings are taken in summer. Select a 12 – 15cm long, pencil-thick section of stem that contains 3 – 4 nodes and trim it to just below a node. Place the stem cuttings around the sides of a pot filled with cutting compost. Olives also root well in pure sand or vermiculite. The application of rooting hormone and/or the use of bottom heat will result in a higher success rate. Place in a bright position away from direct sunlight and keep moist. Roots should appear within 6 – 8 weeks and once well developed can be potted into individual pots.

The Olive Tree can also be propagated by budding and grafting.

Olives: Taxonomy and naming

Family: Oleaceae

Genus: Olea (Latin name meaning ‘greenhouse shrub’;

Species: europaea (Meaning ‘European’)

Synonyms: Many.

See http://www.theplantlist.org/tpl1.1/record/kew-355112 for a full list.

Common names: Common Olive, Cultivated Olive, Edible Olive, European Olive, Lady’s Oil, Olive Oil Plant, Sweet Oil Plant.

Olives: History

The Olive is one of the oldest fruits known to man. Fossil evidence shows that it originates from Italy and the Eastern Mediterranean and has been found going as far back as 20 – 40 million years ago. Fossilised leaves found on the Greek island of Santorini have been dated at 37,000BP (Before Present) and others have been found that are estimated at 60,000BP.

It is believed that Olive trees were first cultivated 7000 years ago in the Mediterranean. Tablets of written evidence, Olive pits and Olive wood fragments have been found in ancient tombs that go back to the Early Bronze Age. It is even suggested that Olive cultivation may have been the source of the wealth of the Minoan civilisation.

Olive oil has long been considered sacred and it is still used today in religious ceremonies around the world. In the Christian Book of Genesis, an Olive branch was brought to Noah by a dove as a symbol that the flood had ended.

The Olive branch is an ancient symbol of peace and the saying ‘to offer an Olive branch’ means to make an offer of peace or reconciliation.

Crowns of Olive branches have, throughout history, been offered to the victors of both games and wars; and Olive oil was the source of the ‘Eternal Flame’ of the original Olympic Games.

An extremely long-lived tree, the Olive has been described on numerous occasions in historical texts, with mentions often found of plantings in the honour of various rulers and famous historical characters many of which, it is claimed, are still living today. Of all the many claims of the oldest specimen, the one with scientific confirmation is a tree in Malta that radiocarbon dating has put at being around 2000 years old.

In modern times, the Olive is one of most extensively cultivated fruit crops in the world with the Mediterranean being the largest commercial growing region producing 95% of the world’s Olives.

Olives: Distribution and Habitat

Olea europaea is native to areas of Southern Europe surrounding the Mediterranean, and also to North Africa. There are six sub-species that are considered naturalised across the Mediterranean, America, Asia and Africa and they grow in a wide range of habitats.

Olives: Appearance

The Olive Tree is a slow-growing, evergreen tree with a very rugged-looking, branching habit. As they age, they develop truly ancient-looking gnarly, twisted trunks and they can reach a height and spread of approximately 10 metres after 20 – 50 years.

Narrow, oblong, leathery leaves measuring 5 – 7cm long and 1 – 3cm wide are grey-green above and silver underneath. Protective cuticles on the leaves help prevent water loss. Short racemes of tiny white, fragrant flowers appear in late summer, from leaf axils on previous years’ wood. Edible, oval fruits follow in autumn and are green in colour, ripening later in the season to purple or a reddy-brown/black colour.

Olives: Conservation

Olea europaea is not listed as being at risk in the wild but, in Southern Italy, there is a very serious threat of localised extinction should the deadly disease Xylella take hold. Original, wild populations in Southern Europe are also at threat of being overtaken by feral plants which are spreading out into the wild from commercial groves. The Olive tree has become a major, woody weed that displaces native vegetation and the problem is not limited to Europe.

In Southern Australia, the seed is spread from cultivated groves by the native Red Fox and many bird species including the Emu. The seeds germinate and grow into a tree with a dense canopy which prevents the regeneration of native tree species.

The presence of oil-rich, highly flammable Olive trees substantially increases the risk of fire in native sclerophylla woodlands – areas that are already very dry and bushfire prone.

Olives: Ecology

Olive trees are not considered to be particularly high in biodiversity. This may be because the flowers are wind pollinated and therefore do not need to produce nectar to attract pollinating insects, but may be also because the fruit is so bitter. The fruits are loved by birds who eat them whole and disperse the seed through their droppings as they travel. Small insects that feed on sap and leaves find the trees attractive, due to the sap’s nutritional properties, and many insects will live in the deep cracks and crevices of the bark.

The Olive tree can thrive under extremely dry conditions, requires very little maintenance and provides shade and cover for wildlife. It is for these reasons that thousands of trees have been planted in arid areas of Israel as part of a study into desertification. So far the research has shown the scheme to be highly beneficial for the local wildlife. Mammal, reptile and bird numbers have all grown since the introduction of the new Olive groves.

Olives: Uses

The prolific Olive tree offers many uses and benefits. Because olive wood is hard and intricately grained, it was popular for handcrafted wooden objects and ornaments, and in the manufacturing of furniture. However, in modern times, its primarily cultivated for olive oil, edible olive fruits, and herbal tea. Its leaves have high levels of hydroxytyrosol and oleuropein, which have proven to offer nutritional and medicinal advantages.

Eating olives straight from the tree won’t kill you or make you ill, but they won’t be palatable as unprocessed olives are extremely bitter. Processing olives breaks down the chemical compounds to give us soft and delicious olives. Different varieties will require different methods but mostly they need to be brined in salty water for a few weeks or months. Fully-grown Olive Trees produce approximately 400 pounds of olives per year while older trees have larger yields.

The Olive has been used throughout all of recorded history. The fruit and oil are of high value nutritionally. They are low in carbohydrates, high in Oleaic acid (a healthy monounsaturated fat), high in antioxidants and are a good source of Vitamin E, Iron, Copper and Calcium. The oil has also been used as fuel for lamps.

Olives are linked to a number of health benefits including decreased inflammation and improved heart health; Olive leaf extract is being tested for its ability to reduce blood pressure. The oil is particularly nourishing for the skin and hair and has been used in personal care rituals throughout history. It is used today in a wide range of cosmetic products.

Olive wood is prized by woodworkers for its durability, grain pattern and colour. Olive wood products are often beautiful but can be relatively expensive to buy due to the lack of wood availability. The tree is slow growing and fairly small and clearly of a higher value commercially when grown for fruit production than when grown for crafting.

Allergy Scale

The Olive tree is rated 10/10 – ‘Extremely Allergenic’, on the OPALS allergy scale. Its allergenic potential is so high because the flowers are wind pollinated.