Olives
Olea europaea
Origin:
The eastern Mediterranean area between Turkey and Syria. Evidence of human use dates back to 9000BC.
Climate:
The olive grows well in a Mediterranean-type climate such as Perth, with cool winters and long hot dry summers. Worldwide cultivation is mainly within latitudes 30-45 degrees at less than 900m elevation. All varieties need sufficient winter chilling (<7°C) to induce flowering, but heavy frosts/freezes (-10°C) will kill trees. Optimum temperatures for shoot growth and flowering are 18-22°C. Water requirements are 500-800mm pa during the critical growth periods. They are not adapted to humid climates.
Plant Description:
It is a hardy long-lived shrub or small tree, 4-8m high. The evergreen leaves which persist for 2-3 years are simple rigid entire decussate lanceolate-elliptic with smooth margins, 3-9 X 1-2cm, and well-adapted to xerophytic climates. Upper and lower surfaces are dark green and silvery-grey respectively. Depth and spread of the root system with cutting-grown plants depends on soil, moisture and aeration.
Relatives:
Oleaceae Family. Olea europaea is divided into 6 subspecies so that the cultivated olive has the complete botanical designation O. europaea subsp. europaea var. europaea. The olive is the only species in the family cultivated for its fruit.
Soil and fertilisers:
Undemanding if they're well-drained, including alkaline soils (pH up to 8.5). Overly fertile soils favour vegetative growth rather than flowering.
Propagation:
Most varieties are propagated taking 30-40 cm cuttings from one-year-old wood, with better results from material towards the base of the tree. There are roughly equal proportions of cultivars with high, medium or low rooting ability. Kalamata is one that is routinely grafted as cuttings are difficult. Seedlings should only be used as a source of rootstocks.
Cultivars:
There are over 1000 varieties worldwide, but many of these are just different names in different regions. Particular cvs usually are better for oil production or pickling, but some are dual purpose. Table varieties are usually larger than those for oil. Manzanilla, Kalamata and Mission/New Norcia are some which can be used either way. Others that can be easily sourced in WA are Verdale, Sevillano, UC13A6 and Barouni. Care should be taken in selection of varieties that cross-pollination and chill hour requirements are met; regularity of bearing and flesh/seed ratio are also important considerations.
Flowering and Pollination:
Paniculate inflorescences that form in leaf axils of 1-year-old wood contain 10-40 small flowers in groups of 3-5. Olives are andromonoecious. In staminate flowers the pistil is absent or non-functional and the proportion of these is governed by cultivar and environment, reaching 50% in adverse conditions. In hermaphrodite flowers there is a green persistent calyx, 4 white-yellowish white petals, 2 stamens and a single pistil with a 2-lobed stigma and superior ovary containing 2 locules that each have 2 ovules. Flowering occurs in spring after winter chill hours have been met, remaining receptive for 3-4 days. Fruit set may be 5% through wind pollination but occasionally also by insects. Only one of the 4 ovules is typically fertilized. Olives can be self-fertile, partially self-fertile or self-infertile, so cross-pollination becomes an important issue with some cvs.
Cultivation:
They should be planted in full sun. Although mature trees will survive through lengthy drought periods, yield will be reduced without appropriate watering . The trees are not nutrient hungry, but yields increase with a balanced fertilizer program where the main application is given in April followed by smaller amounts in September and January.
Wind Tolerance:
Olives are reasonably tolerant to wind and storms
Pruning:
Training the young plant to form a vase system will limit height, maximise light penetration, minimise disease load, and increase aeration and ease of hand harvesting. Most olive cvs have a tendency to alternate bearing, but pruning in heavy ('on') years can reduce this somewhat. Fruit is borne on one-year-old wood.
The Fruit:
This drupaceous fruit is round-ellipsoid, 1-4 X 0.5-2cm, green throughout development and turns dark purple or black at maturity. The edible flesh has 20-30% oil, 3-6% sugars, 2-6 % fibre and good levels of Ca and Fe. Most of the oil is the healthy monounsaturated type. There is a single hard stone (pit).
Fruit Production and Harvesting:
Juvenility for seedlings can last 10 years, 4-6 for those vegetatively propagated. Fruit mature over 6-7 months following fertilization. Table olives are then hand-picked from late February to July in Perth when they're mature green, at colour change or black depending on variety, desired pickling style and product. Kalamata are picked black.
Fruit Uses:
Worldwide commercial production of olives is predominantly for oil production (>90%). In Perth home gardens, table (pickling) varieties are mainly used for culinary purposes but must first be debittered. This normally involves soaking in a 10% salt solution for a few months; a faster process is to use a lye solution. Usually, black olives are less bitter than green and need less processing to become edible. Green or black fruit can be stored in the same salt solution for many years if desired, which is a positive feature given olives are frequently irregular bearers. A few weeks before use, thoroughly rinse the fruit from the brine solution and place into olive oil, plus herbs and spices, if desired.
Pests and Diseases:
The major pests are scale insects such as black scale and olive scale. The olive lace bug is a new pest. Parrots may cause some damage.
Comments:
Commercial orchards range from Geraldton to Albany, with the main area in Gingin. Olives grow and fruit well in Perth home gardens; they are also hardy ornamentals and can serve as a good windbreak. Well-managed mature trees can produce many thousands of fruit per year, 40-50 kg in good years. Alternate bearing behaviour may mean irregular yearly cropping. A commercial proprietary firm in Perth will process for oil, but needs a minimum of 50kg fruit. Olives can be de-bittered by drying (see recipes section).
More Olive info: New Approach to Preserving Olives, Processing Olive Oil, Olives and olive oil – how good are they nutritionally?
