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Olea europaea

Accession Count: 210
Common Name: European olive
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Family Name: Oleaceae
Botanical Name: Olea europaea
Sub Species:
Variety:
Forma:
Cultivar:
Characteristics:
Olea europaea is an evergreen shrub or tree, with a slow to moderate growth rate, typically attaining 30' in height and width, that may live 300-600 years. Its cream-colored flowers are small, clustered, and wind pollinated. Olive trees bloom in spring, and tend toward alternate blooming, producing fruit heavily one year and lightly, or not at all, the next. Some cultivars are self-fruitful, but all fruiting trees have increased fruit set with a second cultivar. The fruit, called olives, are oblong-shaped, fleshy, oil-bearing, bitter, non-poisonous, and thin skinned, with a single hard pit containing a seed. Ripe fruit can be many colors, including red, purple and black. The leaves are lance-shaped, narrow, to 3" long, thick, gray-green on top, and lighter underneath, providing dense shade. The stems have no thorns. The trunk is single or multi-trunked, gray, bumpy, contorted, and gnarled. The extensive root system includes surface roots that can heave walkways and trip pedestrians. 
Compound: Ole eur
Geographic Origin: Eastern Mediterranean
Ecozone Origin: Palearctic
Biome Origin:
Natural History:
The olive tree originated in a region with hot dry summers and cool wet winters. Its wind pollinated flowers seldom involve insects. The fruit attract birds. Rabbits may eat the bark, especially on young trees, and cause great harm. 

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Natural History of the UA Campus Arboretum Specimens: 

Multiple accession planted on the western part of campus were designated University Heritage Trees in 2003. These trees were planted In the early years of the 19th and 20th century, along all walks in the Historic District on the west side of campus. The oldest ones are on the N. side of North Campus Drive and all were planted by Prof. Robert Forbes as part of a variety trial to determine suitability for agricultural use in Arizona. 
Cultivation Notes:
Most fruit-bearing olive trees thrive in USDA hardiness zones 9-11, and are heat and drought tolerant. They need 200-300 chill hours in winter, which for olives, are temperatures above 32°F and below 55°F. Locate these trees in full sun, in well drained soil, spaced 25-30' apart, and away from concrete surfaces that will be stained by the fruit. They accept soil that is dry, low in organic content, with a pH of 5.6-8.5 (acidic to alkaline), and are salt tolerant. Olive trees are better adapted to poor soil than most other fruit trees and seldom suffer nutritional deficiencies. In residential settings, fertilization is unnecessary, even for a good fruit crop. Water and weeding are the most important aspects of olive tree care. 
Once established, deep water once or twice a month in warm months. Avoid locations near frequently irrigated lawns or plants. Some fruiting olive cultivars do poorly in regions with summer rains. No mulch is necessary. Olea europaea begins to flower and fruit after 2-4 years in the ground. The fruit ripen 6-8 months after flowering and are mature when they reach full color. At this time they are ready to drop from the tree. Depending on the cultivar, olives are picked unripe and green for eating, or fully ripe for eating or extracting oil. Dark colored olives, picked when ripe, can be many colors, including red, purple and black. 
Prune the tree to shape in spring, in dry weather, after flowering. Fruit is produced at the tips of the previous year's growth, so avoid winter pruning except to reduce the fruit crop. Remove excess small fruit within 3 weeks of flowering so that two to three fruit are left per foot of branch. This results in larger fruit. Also, cut off any suckers growing from the roots.
Litter is high due to fruit drop, which stains concrete. Spraying the open flowers and leaves with a growth regulator during flowering will stop fruit production. Be sure to spray all flowers and leaves thoroughly. Allow the sprayed surfaces to dry for four to five hours, and deep water the tree for several hours so that it will have sufficient moisture to distribute the growth regulator throughout its tissues.
Olea europaea is propagated by taking cuttings just after fruit set and rooting them in a sand and peat mix. For hard to root cultivars, cuttings are grafted onto hardy rootstock. Seed do not grow true to the parent but can be used to grow ornamental trees. 
Ethnobotany: This tree is used as an ornamental, for its edible fruit, and for oil production which began more than 5000 years ago. Its abundant pollen can be a problem for sensitive individuals and some municipalities allow only sterile, fruitless cultivars in order to reduce pollen levels. Hundreds of cultivars are available, with mature heights ranging from 6' for fruitless dwarf cultivars to 50' for those with fruit. Olives must be processed quickly after harvest, into oil or table olives, to maintain quality. Table olives must be cured, a process that removes bitterness, before becoming palatable. Curing methods for olives are brine curing: fermenting in salt water for up to one year; water curing: each olive is cracked and soaked in daily changes of water for a week or more, then placed in a finish brine with salt and other flavoring elements; dry curing: packing in salt for a month or more; lye curing: using 100% sodium hydroxide with no additives, a method that takes a few days and makes the olives relatively sweet; and sun/air curing: when the fruit is left on the tree to cure, or picked and left to bask in the sun. Once cured, olives are sometimes pitted and dried like raisins. While traditional curing methods often add vinegar to make the olives sour, sugar can be used instead as a sweetener. Modern olive oil extraction is a complex process that involves crushing the clean olives (and their pits) to a fine paste, mixing (malaxing) the paste for 20-45 minutes to allow tiny oil droplets to combine into larger ones, adding water, and using centrifuges to separate oil from paste. Quality is maintained by not exposing the olives to temperatures over 80°F, light or oxygen during the process and by thoroughly cleaning the equipment between each step. The taste of table olives and olive oil is determined as much by the processing operation after harvest as by the cultivar. The term "Cold Pressed" means that no heat was added during oil extraction, and that a press was used to crush the olives to a paste before oil extraction. Centrifuges instead of presses are used to extract the oil except in small operations. The outdated term "Extra Virgin" refers to oil extracted by old fashioned olive presses during the first pressing, and is no longer relevant. It is still used as a dubious indicator of quality and to signify that the oil has a significant amount of olive flavor compounds. Olive oil used for cooking has few to no olive flavor compounds.
Height: 20 - 50 feet
Width: 20 - 50 feet
Growth Rate: Moderate Growing
Grow Season: Summer
Flower Season: Spring
Color: Cream
Function: Shade
Spread: Non-spreading
Allergen: Allergenic
Invasive: Benign
Toxicity: Benign
Hardy: Hardy
Water Use: Low water Use
Citations:

  1. http://ag.arizona.edu/pima/gardening/aridplants/Olea_europaea.html. Retrieved February 19, 2015.
  2. http://www.tropicos.org/Name/23000814 . Retrieved February 18, 2015.
  3. http://www.pollenlibrary.com/Specie/Olea+europaea/. Retrieved February 19, 2015.
  4. http://www.floridata.com/ref/o/Olea_europaea.cfm. Retrieved February 19, 2015.
  5. http://pfaf.org/user/Plant.aspx?LatinName=Olea+europaea. Retrieved February 17, 2015.
  6. http://www.botanical.com/botanical/mgmh/o/olive-06.html. Retrieved February 19, 2015.
  7. http://www.fruit-crops.com/olive-olea-europaea/. Retrieved February 19, 2015. 
  8. Irish, M.  (2008).Trees and Shrubs of the Southwest. Timber Press.

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Olea europaea