“O olive tree, blessed be the earth that nourishes you
and blessed be the water you drink from the clouds
and thrice blessed He who sent you
for the poor man’s lamp and the saint’s candle-light”.
– Folk song from Crete
Scientific Name: Olea europaea
Common Names: Common Olive, Olive
Cultivars: Many cultivars of Olive are useful in bonsai cultivation. Beside those listed look for those with naturally smaller habit and fruit.
“Arbequina” Smaller form, frost resistant.
“Little Ollie” a dwarf cultivar growing only 2-4 feet tall, with dark green leaves.
“Montra” Smaller habit, popular for bonsai.
“Mission” Cold hardy cultivar.
Supspecies Var. Africana. Glossy green leaves above, and brown underneath. Globular, pea-sized fruit. Freely self seeding and considered invasive in some areas.
Other Species for Bonsai: O. laurifolia- Black Ironwood. South African native. Glossy green leaves grow up to 4inches (10cm) and are better suited to larger bonsai. Heartwood is very hard, hence the common name, and is well suited to deadwood styles with the right tools. Zone 9-11
O. oleaster – alternately classified as O. europaea oleaster. Wild olive with smaller leaves.
O. paniculata – Australian Olive. Native to eastern Australia. Bushy tree, 50-80 ft (15-24m) tall in the landscape. Wrinkled bark, glossy green foliage, oval fruit the ripens to a blue-black. Zones 9-12
History: With over 5000 years of cultivation, history, and literature devoted to the olive tree, there is no way to cover all of it in a mere few paragraphs. It is one of the oldest known cultivated trees. It is mentioned in Homer’s Odyssey, Greek and Roman legend (for example, Hercules club is made of olive wood), and the Bible and the Qur’an.
The olive branch, with its characteristic leaf structure is known as a symbol of peace, but also of abundance and glory. The olive is typically associate with Athena, and was often given as an offering to the goddess, as well as presented to the winners of both competitive games and war.
Olives are extremely long lived trees in the landscape. There is a tree that grows on Crete that has been dated through tree-ring dating at over 2000 years old. A tree in Italy as been claimed to be older, perhaps as old as 3000-4000 years. A grove in Spain claims trees that have been carbon dated to over 8000 years old.
Anatomy: Olives are a genus of 20 species of broadleaf evergreens from the family Oleaceae. The Common, or European Olive, which is focused on here, is native to the Mediteranian, Asia and parts of Africa. Because it has been cultivated for over five thousand years though, it is difficult to pinpoint the original, native distribution. Olives have spread across a specific swath of the world in warm-temperate areas, where winters are mild enough for their survival, but still have enough of a chill for the fruiting, commercial aspect of the tree to pay off.
Olives have a broad, spreading habit, ranging from 25-45 feet (8-15m) tall in the landscape, though are often kept even smaller for fruit cultivation. They are tolerant of wind, high altitudes, and a variety of soil conditions. European olives can be found at altitudes from sea level to over 4900 ft (1500m), with other species found at over 8000 ft (2500m).
They have three stages of growth. At the earliest stage, when grown from seed, olive tend to grow only a tap root, using most of the raw energy from this type of root system for trunk development. This stage can last up to seven years. The second stage involves the sprouting of new roots. The crown will often be unwieldy and seem over grown, but will be in proportion with the new roots that have grown. This stage will often be the starting point for airlayered trees. When an olive reaches maturity, the fine, spreading feeder roots begin their growth, the trunk spreading and loosing it’s column form. It is also the point where the previously smooth bark starts to crack and gain a more rugged appearance. The tap root from the earliest stage will disappear eventually, naturally dying off as the larger, spreading root system of the more mature growth takes over.
Foliage: Silvery green foliage, darker on the top, and lighter, almost true silver underneath. The leaves are oblong, coming to a slight point at the ends, and occur alternate and opposite, usually 1 ½- 4inches(4-10cm) long. Olives retain their leaves down to temperatures of around 43F (6c). Leaves are replaces every few years, leaf drop usually occurring at the same time as new leaf growth. The leaves have a waxy coating, and slightly hairy underside, both of which help reduce transpiration and retain moisture during drought.
Stem and Trunk: In immature trees, the bark will be smooth and silver-grey. Over their life time, olive develop naturally gnarled and twisted trunks and branches. Though appearing rugged, the bark and wood beneath can be very soft, and damage easily.
Flowers: Small and fragrant white or cream flowers are borne on previous year’s growth, on long stems at the leaf axils. The occur in clusters, with anywhere from ten to forty blooms. Olives will produce two kinds of flowers, a complete or ‘perfect’ flower with both male and female parts, or flowers with only the male stamen. Olive are largely wind pollinated, as many are self pollinating. Though some varieties produce better fruit when cross pollinated with other plants, and some are completely sterile without other trees to pollinate with. Flowering will only begin after several years, usually once the tree is around seven years old, and increases with age.
Fruit/seeds: The ubiquitous olive fruit, drupes ranging from ½-2 inches (1-5cm), a single seed encased within occur in late summer to early autumn. To encourage setting of fruit, olives require a period of cooler temperatures, as the fruit will only ripen fully in winter. Wild varieties with have smaller, thinner fleshed fruits. Fruits generally start green, ripening to a deep purple, though there are some cultivars that remain green, and others that ripen to a copper brown. Fruits come in a variety of shapes, ranging from round, to oval, and some slightly pointed at one end. Edible, the fruit is too bitter to eat without being treated with brine to remove the oleuropein, a bitter glycoside unique to this species, that causes the unpleasant taste in raw olives. Olives tend to bear fruit cyclically, meaning they will bear very well one year, and not as well the next. There are non-fruiting varieties available, due to their inability to self-polinate.
Hardiness: Zones 8-11. Can tolerate short periods of below freezing temperatures in the landscape, but should be protected from frost in bonsai cultivation, keeping ideally above 43F (6C), as it will retain leaves down to that temperature. It has an extensive, spreading root system, and the fine feeder roots are particularly susceptible to prolonged freezes. Some cultivars are more frost hardy than others, but as cultivars are occasionally mislabeled, it is best to treat an olive as tender. Very tolerant of areas of high temperatures in the summer. Though they can be grown indoors, olives do best if kept outside in summer, and are given a dormancy period in winter where they are kept at below 64F (17C).
Light: Full sun in summer, Olives grow well in hot, sunny locations. Partial shade can be given in winter.
Soil: Olive have a high tolerance for all soil types, though tend to do better in slightly alkaline (calciferous) soils. Consider adding a form of lime in small amounts to the soil. Ensure good drainage and high inorganic content.
Watering: Have a tolerance for drought in the landscape. Water thoroughly, but less frequently, allowing it to stay on the drier side, but never allow to dry out completely in pot culture. Olives have evolved to be water opportunists, meaning that when water is available, they will take it up readily and quickly, but sustaining themselves when water is scarce. The rate an olive may take up water when it is abundant can lead to a mistaken assumption that they constantly need high levels of water. Resist the urge to over water your olive.
Fertilizer: Balanced feed through the growing season. Dose two or three times in autumn with a nitrogen free formula before winter. Do not feed through winter. Olive can benefit from an application of trace elements once a year.
Pests and Diseases: Aphids, black scale and spider mites. Certain lepidopterous caterpillars. Verticillium wilt, Anthracnose and Olive Knot (caused by the bacterium Pseudomonas savastanoi). Olive fly in Europe.
Repotting: Every two to three years as needed for younger trees, longer for more mature specimens. Cut back up to a third of the root mass, leaving as much of the fine feeder roots as possible, while pruning heavy roots back hard.
Pruning and Styling: Pinch back new growth as needed during the growing season. Pinching back during the growing seasons (spring or autumn) will result in backbudding all over the tree. Do not pinch back if you want to encourage back budding and ramification however if temperatures are below 50F(10C) or above 100F(35C). Pinching between these temperatures will also encourage smaller leaf size and shorter internodes. Remove buds growing directly up and down. New growth will be three colours. First green, then purple, and finally tan. Green shoots will ramify less than those that are purple or tan. Young trees can be pinched back to 1 to 3 leaves, depending on the direction of the last remaining bud(the direction the new shoot with grow) when growth is purple or starting to turn tan. Older and more mature trees, where ramification is closer to complete, pinching can be done when the shoots are green or almost purple.
When larger branches are cut during the growing season, it will result in coarse, vigorous, and often times congested new growth at the site of the cut, which, if left unchecked, can cause inverse taper. Rub off unwanted buds as they grow to prevent that problem when pruning larger branches. To avoid the problem all together, prune unwanted shoots that are not needed to thicken an existing branch or trunk as early as possible. Also try pruning large branches (1in, or 2.5cm or more) in late autumn or winter when growth has slowed. Olives can be unpredictable in their reaction to heavy branch pruning, and shortening of these can sometimes cause the entire branch to dieback, new shoots emerging from the trunk.
Wire: Olive can be very brittle, and the bark and wood are easily damaged, so take care wiring, and only do so when necessary. Wire young branches, under 3 years old with care, in late autumn or winter. Use raffia when wiring larger or older branches to avoid damage.
Leaf Reduction: A combination of pot culture, good pinching techniques and sun will reduce the leaf size.
Jin/Shari: Though deadwood is often seen on olive in the landscape, the wood of the olive rots easily. If there is deadwood on a collected specimen, be sure to treat it with lime sulphur and possibly additional wood hardeners/preserver.
Styles and Forms: All styles except formal upright, broom and exposed root (though extensive, the root system is delicate and can be easily damaged by this style).
Seeds: Pits from jarred olives will not germinate, the brine kills them. Seeds do not always breed true to the parent tree, and are difficult to germinate, sometimes with as low as a 30% success rate. Soak in hot water or an alkaline solution for 24 hours before planting in early spring.
Cuttings: Best method. Take cuttings in late spring to early summer. Semi-hardwood cuttings, up to a half inch (1.75cm) in diameter and 4-6in (10cm-15cm) long with root the most easily. Remove all leaves but 2-4 sets at the top of the cutting. Use rooting hormone to increase chances. Greenwood cuttings are not always mature enough to root. Try using a mix of 90% sand or perlite and 10% peat moss. Keep misted, but not soaking. Addition of bottom heat is helpful, and will increase cutting viability dramatically. Rooting of hardwood cuttings can be done, though can take several months. Semi-hardwood cuttings can also be rooted sometimes in straight water.
Truncheon: A truncheon method involves removing a branch, 3-4in (7.5-10cm) in diameter from a tree, cutting it into 12in (30cm) lengths and planting it horizontally in well tilled, aerated soil. New shoots will often grow, and these can later be separated, or used to create a joined root planting.
Other: Ovuli are swellings found on the trunks of many olives. These can be cut off and planted in early spring, and will root easily. These structures contain both adventitious root initials and dormant buds so that new root and shoot systems can develop. This process however is damaging to the parent tree, and will leave a large scar. Olive can also be propagated by removing suckers in spring.
Other Facts and Trivia:
-“In Greek and Roman mythology the olive tree was the symbol of Athene or Minerva, goddess of medicine and health. Her gift of the olive to mankind was judged greater than Poseidon’s gift of the horse, and for this reason Athens was named in her honor. In modern Italy an olive branch hung over a door is supposed to keep out devils, witches, and evil spirits. Many legends concerning the olive occurred among medieval Christians and are still believed in many sections, among which is the following, which exists in many variations. A seed each of the olive, cypress, and cedar is said to have been given to Seth for his dying father, Adam, by the angel guarding the Garden of Eden. Planted in Adam’s mouth, they eventually grew up into a single tree with three trunks, one of olive, one of cypress, and one of cedar wood. Beneath this tree David wept in contemplation of his sins. The tree was felled by Solomon, but the timber could not be hewn and was therefore cast into a marsh, where it floated and formed a bridge for the Queen of Sheba. Finally, the wood was fashioned into the cross on which Jesus was crucified.” – “Plants of the Bible” Harold N. Moldenke, Alma L. Moldenke
-“Some trees on the Mount of Olives and at Gethsemane are said to have been there since the time of Christ; but this is not very probable since the Roman emperor, Titus Vespatian in 70 A.D. is reported by contemporary historians as having cut down all the olive trees there. It is very difficult, however, to kill an olive tree by cutting it down, because new sprouts are sent up from the root and all around the margins of the old stump, often forming a grove of 2 to 5 trunks, all from a single root, where originally was only one tree. – “Plants of the Bible” Harold N. Moldenke, Alma L. Moldenke
-“His branches shall spread, and his beauty shall be as the olive tree…” – Bible, Hosea 14:6
-“Lit from a blessed Tree, an Olive, neither of the east nor of the west, whose oil is well-nigh luminous, though fire scarce touched it: Light upon Light!” Qu’ran 24:35
Olives in Nature:
Reference.com on the Olive tree http://www.reference.com/search?q=olive%20tree
BCI Olive entry: http://www.bonsai-bci.com/species/olive.html
CRFG Olive Facts: http://www.crfg.org/pubs/ff/olive.html
Evergreen Garden Works: Olive- http://www.evergreengardenworks.com/olive.htm
The Olive Oil Source: http://www.theoliveoilsource.com
Bonsai Survival Manual Colin Lewis, 1996
Trees and Shrubs Ernie Wasson, Tony Rodd, 2004
Trees of the World Tony Russel, Catherine Cutler, Martin Walters, 2006