Fruit Facts from
the
California Rare Fruit Growers, Inc.
Olive
Olea europaea L.
Oleaceae
Common
Names: Olive
Related Species: Wild Olive (Olea africana), Oleaster (O. europaea var. oleaster).
Distant Affinity: American Olive (Osmanthus americana), Fragrant Olive (O. fragrans).
Origin:
The olive is native to the Mediterranean region, tropical and central
Asia and various parts of Africa. The olive has a history almost as
long as that of Western civilization, its development being one of
civilized man's first accomplishments. At a site in Spain,
carbon-dating has shown olive seed found there to be eight thousand
years old. O. europaea may
have been cultivated independently in two places, Crete and Syria.
Archeological evidence suggest that olives were being grown in Crete as
long ago as 2,500 B.C. From Crete and Syria olives spread to Greece,
Rome and other parts of the Mediterranean area. Olives are also grown
commercially in California, Australia and South Africa. There is some
disagreement over when the trees first appeared in California. Some say
they were introduced in 1769 when seeds brought from Mexico were
planted. Others site the date 1785 when trees were brought in to make
olive oil.
Adaptation:
The olive requires a long, hot growing season to properly ripen the
fruit, no late spring frosts to kill the blossoms and sufficient winter
chill to insure fruit set. Home grown olives generally fruit
satisfactorily in the warmer coastal valleys of California. Virtually
all U.S. commercial olive production is concentrated in California's
Central Valley, with a small pocket of olive acreage outside Phoenix.
The tree may be grown as an ornamental where winter temperatures do not
drop below 12° F. Green fruit is damaged at about 28°, but ripe fruit
will withstand somewhat lower temperatures. Hot, dry winds may be
harmful during the period when the flowers are open and the young
fruits are setting. The trees survive and fruit well even with
considerable neglect. Olives can also be grown in a large container,
and has even appeared in shows as a bonsai.
Description
Growth Habits: The
olive is an evergreen tree growing to 50 ft. in height with a spread of
about 30 ft. The tree can be kept to about 20 ft. with regular pruning.
The graceful, billowing appearance of the olive tree can be rather
attractive. In an all-green garden its grayish foliage serves as an
interesting accent. The attractive, gnarled branching pattern is also
quite distinctive. Olives are long-lived with a life expectancy of 500
years. The trees are also tenacious, easily sprouting back even when
chopped to the ground.
Foliage:
The olive's feather-shaped leaves grow opposite one another. Their skin
is rich in tannin, giving the mature leaf its gray-green appearance.
The leaves are replaced every two or three years, leaf-fall usually
occurring at the same time new growth appears in the spring.
Flowers:
The small, fragrant, cream-colored olive flowers are largely hidden by
the evergreen leaves and grow on a long stem arising from the leaf
axils. The olive produces two kinds of flowers: a perfect flower
containing both male and female parts, and a staminate flower with
stamens only. The flowers are largely wind pollinated with most olive
varieties being self-pollinating, although fruit set is usually
improved by cross pollination with other varieties. There are
self-incompatible varieties that do not set fruit without other
varieties nearby, and there are varieties that are incompatible with
certain others. Incompatibility can also occur for environmental
reasons such as high temperatures.
Fruit:
The olive fruit is a green drupe, becoming generally blackish-purple
when fully ripe. A few varieties are green when ripe and some turn a
shade of copper brown. The cultivars vary considerably in size, shape,
oil-content and flavor. The shapes range from almost round to oval or
elongated with pointed ends. Raw olives contain an alkaloid that makes
them bitter and unpalatable. A few varieties are sweet enough to be
eaten after sun drying. Thinning the crop will give larger fruit size.
This should be done as soon as possible after fruit set. Thin until
remaining fruit average about 2 or 3 per foot of twig. The trees reach
bearing age in about 4 years.
Culture
Location:
Plant olive trees in full sun and away from sidewalks to avoid stains
from fallen ripe fruit. Non-fruiting trees are available which can be
planted in areas where fruit may be a problem. Strong winds will
"sculpt" the trees, but otherwise they are quite wind-tolerant.
Soils: Olives will grow well on almost any well-drained soil up to pH 8.5 and are tolerant of mild saline conditions.
Irrigation:
Irrigation is a necessity in California with its dry summers. A monthly
deep watering of home grown trees is normally adequate. Because of its
small leaves, with their protective cuticle and slow transpiration, the
olive tree survives even extended dry periods.
Fertilization:
Fertilizing olive trees with additional supplies of nitrogen has proved
beneficial. In California farmers systematically apply fertilizers well
ahead of the time flowers develop so the trees can absorb the nitrogen
before fruit set. Many growers in Mediterranean countries apply organic
fertilizers every other year.
Pruning:
Proper pruning is important for the olive. Pruning both regulates
production and shapes the tree for easier harvest. The trees can
withstand radical pruning, so it is relatively easy to keep them at a
desired height. The problem of alternate bearing can also be avoided
with careful pruning every year. It should be kept in mind that the
olive never bears fruit in the same place twice, and usually bears on
the previous year's growth. For a single trunk, prune suckers and any
branches growing below the point where branching is desired. For the
gnarled effect of several trunks, stake out basal suckers and lower
branches at the desired angle. Prune flowering branches in early summer
to prevent olives from forming. Olive trees can also be pruned to
espaliers.
Propagation:
None of the cultivated varieties can be propagated by seed. Seed
propagated trees revert to the original small-fruited wild variety. The
seedlings can, of course, be grafted or chip budded with material from
desired cultivars. The variety of an olive tree can also be changed by
bark grafting or top working. Another method of propagation is
transplanting suckers that grow at the base of mature trees. However,
these would have to be grafted if the suckers grew from the seedling
rootstock.
A commonly practiced method is propagation from
cuttings. Twelve to fourteen inch long, one inch wide cuttings from the
two year old wood of a mature tree are treated with a rooting hormone,
planted in a light rooting medium and kept moist. Trees grown from such
cuttings can be further grafted with wood from another cultivar.
Cutting grown trees bear fruit in about four years.
Pests and diseases:
The olive tree is affected by some pests and diseases, although it has
fewer problems than most fruit trees. Around the Mediterranean the
major pests are medfly and the olive fruit fly, Dacus oleae. In
California, verticillium wilt is a serious fungal disease. There is no
effective treatment other than avoiding planting on infested soils and
removing damaged trees and branches. A bacterial disease known as olive
knot is spread by pruning with infected tools during rainy months.
Because the olive has fewer natural enemies than other crops, and
because the oil in olives retains the odor of chemical treatments, the
olive is one of the least sprayed crops.
Harvest:
Olive fruits that are to be processed as green olives are picked while
they are still green but have reached full size. They can also be
picked for processing at any later stage up through full ripeness. Ripe
olives bruise easily and should be handled with care. Mold is also a
problem for the fruit between picking and curing. There are several
classical ways of curing olives. A common method is the lye-cure
process in which green or near-ripe olives are soaked in a series of
lye solutions for a period of time to remove the bitter principle and
then transferred to water and finally a mild saline solution. Other
processing methods include water curing, salt curing and Greek-style
curing. Explicit directions for various curing and marinating methods
can be found in several publications including Maggie Blyth Klein's
book, Feast of the Olives, and the University of California
Agricultural Sciences Publications Leaflet 21131. Both green-cured and
ripe-cured olives are popular as a relish or snack. For California
canned commercial olives, black olives are identical to green olives.
The black color is obtained by exposure to air after lye extraction and
has nothing to do with ripeness. Home production of olive oil is not
recommended. The equipment required and the sheer mass of fruit needed
are beyond most households.
Commercial Potential:
Commercial olive production is a multimillion dollar business in
California. In the Mediterranean region olives and olive oil are common
ingredients of everyday foods. Raw olives are sometimes sold in
speciality produce stores, and home growers in California often sell
their excess crop to others interested in home curing. There is also a
growing interest in specialty olive oils, often produced commercially
from small groves of olive trees.
Cultivars
Over
the centuries mankind has produced and propagated a myriad of olive
varieties. Today several dozen varieties are grown commercially around
the world. Five commercially important varieties are grown in
California: Manzanillo, Sevillano, Mission, Ascolano and Barouni,
listed in descending order of crop size. Some representative olive
cultivars including the commercial California varieties are listed
below.
Ascolano
Very large, ellipsoidal fruit. Skin color very light even when ripe,
pit very small. Fruit is tender and must be handled carefully. Contains
very little bitterness and requires only moderate lye treatment.
Excellent for pickles, but needs proper aeration during pickling to
develop "ripe" color. Tree a heavy bearer, widely adapted.
Barouni
Large fruit, almost as large as Sevillano. Trees spreading and easy to
harvest. Withstands extremely high temperatures. The variety usually
shipped to the East Coast for making home-cured olives. Originally from
Tunisia.
Gordal
Medium to large, plump fruit, ripening early. Resembles Sevillano. A
popular pickling olive and principal cultivar in Spain, producer of
most of the world's table olives.
Manzanillo
Large, rounded-oval fruit. Skin brilliant purple, changing to deep
blue-black when mature. Resists bruising. Ripens early, several weeks
earlier than Mission. The pulp parts readily with its bitterness and is
exceedingly rich when pickled. Excellent for oil and pickles. Tree
spreading, vigorous, a prolific bearer.
Mission
Medium-sized, oval fruit. Skin deep purple changing to jet-black when
ripe. Flesh very bitter but firm, freestone. Ripens rather late. Good
for pickling and oil, specially ripe pickles. Most widely used for
cold-pressed olive oil in California. Tree vigorous, heavy-bearing.
More cold resistant than other cultivars. Grown at the old missions in
California.
Picholine
Small, elongated fruit. Skin light green, changing to wine red, then
red-black when ripe. Pulp fleshy, firm-textured. Tree vigorous,
medium-sized, bears heavy crops regularly. Cured olives have a
delicate, subtle, lightly salty, nut-like flavor. Usually salt-brine
cured. Popular in gourmet and specialty markets.
Rubra
Medium-small, ovate fruit. Skin jet-black when ripe. Ripens 3 to 4
weeks earlier than Mission. Best suited for oil, but is also used for
pickling. Tree large, precocious, often producing fruit the second
year. An exceptionally prolific bearer. Very hardy and reliable even in
dry situations. Originated in France.
Sevillano
Very large fruit, bluish-black when ripe. The largest California
commercial variety. Stone large, clinging. Ripens early. Low oil
content, only useful in pickling. Used for making Sicilian style salt
brine cured olives, also the leading canning cultivar. Tree a strong
grower and regular bearer. Require deep, rich, well drained soil. Will
not stand much cold.
Further
Reading
Bianchini, Francesco and Francesco Corbetta. The Complete Book of Fruits and Vegetables. Crown Publishers. 1976.
Facciola, Stephen. Cornucopia: a Source Book of Edible Plants. Kampong Publications, 1990. pp. 142-143.
Ferguson,
Louise, G. Steven Sibbett and George C. Martin. Olive Production
Manual. University of California, Division of Agriculture and Natural
Resources: Publication 3353. 1994
Hartmann, H.T., K. W. Opitz and J.
A. Beutel. Olive Production in California. University of California,
Agricultural Sciences Publications: Leaflet 2474. 1980.
Klein, Maggie Blyth. The Feast of the Olive. Chronicle Books. 1994
Stebbins, Robert and Lance Walheim. Western Fruit and Nuts. HP Books, Inc. 1981. p. 108.
York,
George. ABC's of Home-Cured, Green-Ripe Olives. University of
California, Agricultural Sciences Publications: Leaflet 21131.
1979.
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