Download Olive Trees/Shrubs Olea europeaea (European olive) Family

Olive Trees/Shrubs
Olea europeaea (European olive)
Family: Oleaceae
Description
Olive trees/shrubs are evergreen, averaging in height from 24-49 ft. with a broad spreading crown and
extensive shallow root system. A young tree’s smooth trunk develops a gnarled and twisted form with age. Oblong
willow-like foliage is silvery green in color. Small white feathery flowers are borne on previous year’s wood in
racemes formed at the axilis of leaves. Olives produced are considered a stone fruit ranging in size from .4-1”. Fruit
is harvested for eating and oil extraction. There are six natural subspecies but now hundreds of cultivars are
available.
History
Olea europeaea are native to the Mediterranian, Asia and Africa. Recently archiologists located specimens
on the Greek island of Santorini dating 37,000 years ago. These specimens included white fly traces indicating an
animal-plant co-evolution. First wide-spread evidence of Olea europeaea was in the areas of Persia and
Mesopotamia 6-7000 years ago. Cultivation near human population is evidenced 5-6000 years ago with
commercial growing developing around 3000BC for harvesting of fruit for consumption, oil for cooking, lighting,
grooming, ceremonial uses and hard wood for building.
Spanish colonists brought olive trees to the Americas first in 1560 Lima, Peru. Cultivation followed the
coastal valleys and eventually were introduced to California in the 18th century by missionaries at Mission San
Diego de Alcala. By 1860, commercial agriculture was established in the region.
Sacred references to olive trees, fruit, oil, etc. appear in a wide variety of early religious writings as well as
cultural/governmental celebrations. Olive oil was used by the Greeks to light the first eternal Olympic flame with a
crown of olive leaves awarded to the victors. An olive branch extended represents an offering of peace and may
also signify abundance, glory and fertility.
Cultivation
It was once thought that olea europeaea would only grow successfully within 34.5 miles from the sea.
Expanded areas of cultivation are now recognized where a hot dry summer and freezing point above 14 degrees F.
is evident but Mediterranian coastal climate ranks high. Trees are hardy in zones 8, 9, 11-24. Olives are now one of
the most extensively cultivated fruit crops in the world with twice as much agricultural land than apples, bananas
or mangoes. Only coconut trees and oil palms are more cultivated as this time.
The preferred growing medium is calcareous soil, limestone slopes, light soil, well drained clay or poorer
soil. Rich soils increase the possibility of disease, thus once yearly fertilization is recommended in order to reduce
the occurrence of root burn from salt build up in the soil. Wide spacing, 20 ft., between trees is recommended to
accommodate expansive root systems.
Trees must be propagated from cuttings, as plants from seeds revert to wild thorny trees with small fruit.
Plants are only partially self-fertile so pollenizers are required for high production of fruit. Even with pollenization,
crops may alternate between high and low production years. Trees produce well into old age with documentation
supporting reports of productive trees over 2000 years old.
Pests, Diseases, Weather
The olive fruit fly, Dacus oleae or Bactrocera oleae lays eggs in the olive just before it becomes ripe in
Autumn. The area surrounding the puncture rots, becomes brown and results in bitter tasting olives and oil thus
destroying the crop. Traditional treatment is with insecticidal organophosphate e.g. dimethoate. Organic
treatment uses trapping the fruit fly with bait containing spinosad, bacterium Bacillus thuringiensis or spraying
kaolin clay which acts as a barrier. Picking up waste from trees is essential to preventing spread.
Lepidopterous caterpillars eat leaves and flowers. Black scale bug looks like a black spot and has wasps as
their predator. The curculio beetle eats edges of leaves leaving a sawtooth pattern. Rabbits eat bark. Voles and
mice eat roots. Nematodes may also invade roots.
Trees may be attacked by fungus, Cycloconium oleaginum and bacterium Pseudomonas savastanoi pv.
oleae.
Heavy frost can damage trees but roots may regenerate growth accounting for longevity. Gales and
heavy rains during harvest also may damage trees and crops.
Home Gardening Tips
* “Arbequina” a Spanish variety is recommended for fruit and oil in home gardens.
* Provide broad canopy for shade.
* Easily transplanted and rarely diein the process so move them if they are in the wrong place.
* Drought tolerant.
* Fire resistant.
* Roots are shallow and invasive so beware of sidewalks, driveways, patios. If root barriers are required
to prevent or reduce damage, stainless steel that comes in a roll is the best.
* Harms lawn.
* Olives stain cement and olive oil can prevent oil slurry coats on driveways from adhering properly.
* Pollen is highly allergenic and may trigger asthma.
* In some countries, eg. Australia, olive trees are considered invasive. Seeds are being spread by
introduced red foxes and birds. With their close, broad canopy, light reduction inhibits regeneration of
native trees.
Sources
The New Sunset Western Garden Book, 2012
Patwalsh.com
Homeguides.sfgate.com
Wikipedia
Submitted by: Pam Kirpalani, MG Class of 2016