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Olive Trees in the Mother Lode

Although olives have been grown in this area for over one hundred years, there has been a resurgence of olive tree orchards in the Mother Lode over the past several years. There are different trees for different olive products. This article will provide information about the properties of each.

First, olives were introduced by gold prospectors when they turned from processing ore to farming as a way to make a living. They realized that the soil here was similar to that of the Mediterranean region. Those early olive crops went into olive oil production, but in the early 1900’s the industry shifted, as canning technology resulted in higher returns for table olives than for oil. Today, 90 percent of California’s olive production is for canned olives and only 10 percent crushed for oil. Spain is just the opposite. It is the world’s leading olive producer and grows 90 percent of its crop for oil and 10 percent for cured olive products. Spain has 5.6 million acres of olives compared to California’s 40,000 acres. In California, health-conscious consumers have led a revival in olive oil as a flavorful alternative to vegetable oils.

Our soil is marginal in many areas, but olive trees are very forgiving and tolerant of their growing conditions. Some trees grow for a few hundred years. There are many varieties of olives; some are better used for olive oil, and others are better for fruit.

The following information is provided by the University of California: “The olive tree is an evergreen tree that performs best in hot dry areas of California. It is an attractive ornamental and does not tolerate wet winter soils. Trees should be spaced 16 – 20 feet apart. Olives for canning and pickling are usually harvested in September and October. Heavy crops of small fruit unsuited for canning and pickling are left on the trees until January and harvested for their oil. The backyard orchard is not economical for oil production and cannot compete with commercial growers.”

Some popular table varieties of olives are grown in this area. Ascolano has large fruit and is the most cold hardy. The oil is very aromatic. Manzanillo, which is the main variety used for the black “California” style olive, is also grown in this area. This medium size tree is susceptible to cold injury.

If you want oil, try Arbequina. This variety from northern Spain produces a very high quality of fruity oil. Frantoio, an Italian variety, is used as one of the main ingredients in gourmet olive oil production. Many olive oils are blends of several varieties of olives. The Mission variety of olive can be used for either table fruit or oil. This tall tree is very cold tolerant.

If you do decided to grow olives, here is a handy calendar for backyard olive production:

In the winter dormant season, spray with fixed copper to prevent peacock spot, especially in wet years. Trees should be pruned during the bloom period. To reduce alternate bearing, remove more shoots from trees with heavy bloom and skip trees with light bloom. Fertilize mature trees with 2 lbs of urea or 50 lbs. of compost. Begin irrigating trees so there is no water stress during bloom. As the season moves to summer, control weeds with organic mulch or cultivation, especially on young trees.

Fertilize young trees with one ounce of urea under each drip emitter once per month from May to September. Apply drip irrigation every day according to water use requirements. Harvest season is in the fall. For table fruit, harvest when the fruit is still green, just before the straw yellow stage. For oil, harvest when the fruit has turned black on the outside but the flesh is still green / yellow. Continue irrigation right up to harvest if weather is dry; do not allow fruit to shrivel. Again, apply fixed copper to prevent peacock spot before the first major fall rains. Wash copper off fruit prior to processing or apply copper to trees after harvest.

Olive trees generally do well here in the Mother Lode. You can find several estates with plentiful trees that produce very good products for the consumer. Best of all, the olive tree is drought tolerant.

Jim Gormely is a University of California Cooperative Extension Master Gardener of Tuolumne County.