January 26, 2013
In the French Riviera where the Alps plunge steeply into the Mediterranean, there is a large, venerable olive tree just outside the medieval walls of the perched village of Roquebrune.
Still producing fruit, the tree thrives in rocky limestone earth. Biologists estimate the tree is at least 2,200 years old. The botanical ancestor of the olive is Oleaster olea sylvestris. Native to Asia Minor, its descendant, Olea europea, thrives in areas with a Mediterranean climate, including California where it was introduced by Spanish missionaries in 1769 at Mission San Diego. Olive trees like it hot in the summer with a slight winter chill.
Its opposite leaves, lance-shaped with grayish hairy undersides, slow the rate of transpiration; important in a dry climate. Each leaf grows over a two-year period and yellow leaves in the spring signify the abscission process. Most olive trees are self-fertile, but production can be increased with cross-pollination. Pollination is achieved with wind moving the pollen. The fruit of the olive is a drupe, botanically similar to apricots, cherries, peaches and plums. Full bloom occurs in May with fruit maturing on average in November.
Because the olive tree can flourish even in the most barren soil, it has long been a symbol of glory and peace, its oil used to anoint kings (branches of olives were found in Tutankhamen's tomb) and its leaves to crown athletes (in the first Olympiad).
But the fruit, born every other year, is not edible without processing as it contains the bitter glucoside oleuropein. Several simple methods to remove the bitterness include mixing the olives with salt in a bowl or soaking them in a strong salt solution (one cup of salt per quart of water) and changing this twice a day until the fruit is no longer bitter (about two weeks).
Pests and disease are best managed with good cultural practices including water management, proper pruning and clean up of fallen debris and fruit. Two common pests are the olive fruit fly and peacock spot. Hanging a trap filled with Torula yeast tablets and water in each tree can control olive fruit fly. The traps can be purchased online. Peacock spot has a characteristic yellow halo around the spot. This disease reduces productivity, but can be controlled by applying a copper fungicide in late fall before the rainy season.
To select the best cultivar to plant in your garden, several factors may assist in the selection process. The first step is to select your spot. Remember, olives thrive in poor soil, love full sun and require good drainage. Next, develop your criteria. Do you want to eat the olive, make oil with it or both? How much time do you want to spend pruning and picking? When do you want to harvest? And lastly, if you will participate in community press days, coordinate those dates with the harvest date of the cultivar you select.
Choose the best olive tree that's suitable to your microclimate in Marin. Plant the right plant in the right spot, and your reward will be many years of seductive fruit!