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OLEA EUROPEA L. - Olive. |
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CULTURE |
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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.
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.
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CULTIVARS |
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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.
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