Farming Olive Trees for Oil

"Plant grapes for your children, plant olive trees for your grandchildren"

Throughout the Mediterranean Basin, wherever there are grape vines, there are olive trees. The picture is so characteristic and expected that you probably don't even give it a second thought. Today in San Diego County, when you drive around any city, suburb, or country road you'll see olive trees and grapes thriving in this Mediterranean climate. Olive trees have been in San Diego since the first Spanish missionaries trekked across the desert with their precious cuttings.


There are over 500 varieties of olive trees actively cultivated throughout the world. You might be surprised to learn that green olives and black olives are not part of the list. All olives start out green and turn purple and black as they ripen. Here in San Diego County any variety you might like will grow with little effort. Most of the roadside and front yard trees here are direct descendants of the missionary's treasured cuttings. In fact, most of them are the "Mission" varietal, a type originally imported from Spain but hardly seen there now.

Each region of the Mediterranean Basin has its favorite varietal. The olives look different, taste different, and make unique oil. That oil is loved by its native supporters like part of their birthright. There is no 'best oil' or 'proper oil'. In fact there are cook books dedicated to the idea that each varietal can be used to uniquely enhance different foods.

So what should you plant? If you have a favorite oil that comes from your homeland or has impressed you during your travels, you can plant that varietal. If you have trees growing on your property, they can be loved and nurtured to make respectable oil.

The world of olive oil is huge. It is a commodity product that is shipped and traded; honored and diluted; packaged in cans and bottles; sold in supermarkets and specialty stores - everywhere. If you are going to contribute to an outstanding and marketable oil you need to look at what the knowledgeable consumer values.

Here in California the most valuable oil, and the most valuable olives that make that oil, are modeled after Italian Tuscan blends. These oils command the highest prices. In 2013 the oil from Tuscan varietals is worth more than twice as much as "California native" varietal oils. That is a significant market to target. The makers of Ramona Gold Extra Virgin Olive Oil recommend a Tuscan mix of 40% Frantoio, 30% Leccino, 20% Maurino or Moraiolo and 10% Pendolino for pollination. This is the mix you find in the fields of Southern Tuscany.

Soil Preparation

The soil in the Ramona Valley is ideal for olive trees. It is loose and gravelly, not too fertile, and rich in minerals. Yes, that is the same type of soil that grapes favor. Unlike grapes, however, olive trees are very shallow rooted. The root-zone of olive trees extend less than 12 inches beneath the surface. Also, olives like a slightly more basic soil acidity. Sometimes it helps to add a little lime to the soil around olive trees.

Because the roots are so shallow, the soil does not need to be deep-ripped before planting. If you've got 12 inches of usable soil, not clay, rock or compressed surface, you can plant an olive tree. But also, because the roots are so shallow, olive trees are competing with weeds and grasses for the soil moisture in that 12 inch deep zone. Weed control must be considered when choosing a site.


Olive trees are born to survive drought conditions. There are thousand-year-old trees in the Mideast that have never been irrigated and still produce fruit. A mature tree can live on the pittance of water available in San Diego County. Olive trees bear fruit in alternate years even during drought conditions.

However, if you want to produce fruit year-after-year in sufficient quantity to make olive oil, trees need irrigation. Plan to shallow water under the leaf canopy. Deep watering is wasted because after a couple hours, the water is well below the olive tree's root-zone. The irrigation can be drip system, drip-mounted sprinklers or underground (avocado-style) sprinkler systems. Unlike avocados, the water used for olives is measured in acre-inches instead of acre-feet.

Olive trees bloom early in the spring. The flowers set fruit based on water quantity that year. Irrigation in the late winter and early spring enhances fruit set. Because of the adequate water the tree is convinced that it's a good year for creating fruit. In decomposed granite it is hard to over-water olive trees. In clay or loam soil avoid drowning the roots in standing water.

Obtaining Trees

There are a few nurseries in California that specialize in olive trees. The ones that have excellent trees and instructive web sites are Santa Cruz Olive Tree Nursery ( and NovaVine (novavine/olives/).

Also, here in Ramona on Highland Valley Road, the new RP Nursery ( carries an ample inventory of olive trees well suited to oil production. They are careful to stock the Tuscan varietals.

Planting Trees

Olive trees can grow to be quite large. There are old trees of the Mission variety right here in Ramona that are larger than oak trees and just as majestic. These trees are quite difficult to harvest because they are so tall.

When planning an olive grove, plan for trees that are pruned to 12 feet tall and a similar diameter. These trees are easier to harvest and will produce fruit consistently throughout the years. Trees can be planted in rows or scattered across a hillside. In a vineyard environment, the trees can fill in the spaces where the slope is too steep for vines. They should be spaced so that they are about 12 to 15 feet apart in all directions. Any closer and they grow together into a dense, unhealthy and under-performing clump.

Pest Control

Since we pick olives while they are still under-ripe, we don't have to worry about bird pests. Even squirrels won't bother the olives. One quick bite will convince a bird or squirrel that better eating is available next door at the avocado or peach orchard. The un-ripe olives are extremely bitter. It was a brave man who first discovered the magic of olive oil or the secret of cured olives.

However, as usual in San Diego County, there is an imported insect pest that thrives here. The weather is mild, there are thousands of untended olive trees, and the wind will carry insects across miles and neighborhoods in the blink of an eye. These insects are the "Mediterranean Olive Fruit Fly". This fly deposits eggs starting when the olive fruit is just 7mm in diameter (the size of a pea). The hatched larvae crawls around inside the fruit, eating as it goes. The olive is soon turned into a soft, tunneled and potentially mildewed mess. If you have more than 10% damage to your fruit the quality and quantity of the oil will be compromised. Olive Fly damage is easy to miss unless you examine each olive looking for the tiny exit wound as mature flies emerge for more rampage.

You can set out baited traps for the flies. These will tell you that flies are present, but traps are not effective in reducing the fruit damage. Instead, there are two approved organic treatments that really do reduce the damage. One is kaolin clay (Surround) that coats the entire tree in a white powder. Somehow the flies don't like white fruit, they prefer 'olive green'. The clay needs to be applied to every tree that has fruit about once a month - more often if we get a rare summer rain.

The other treatment is a bait spray (GF-120 NF Naturalyte) that is sprayed on a single branch every two weeks. The 12" circle of molasses-like spray is placed on the north side of the tree. The flies are attracted to the bait before they lay eggs, and when they eat the bait they also consume the organic pesticide "spinosad". They die quickly without laying eggs. It is best to spray alternate rows weekly so that there is always fresh bait protecting the fruit.

As usual, UC Davis has the definitive word on the pest at:

It was just 1998 when these pests were found in California! Imported plants or fruit were not properly inspected in Los Angeles and they spread like wildfire. After fighting these guys for a couple years you will think wistfully back to the day, only 15 years ago, when olive growing in California was just 'plant and pick'.


There seem to be a million theories of olive tree pruning, one for every neighborhood in the Mediterranean Basin that has an olive growing tradition. I've read all the books, watched all the videos and looked at groves in France, Italy and Greece. If you figure it out, please call me.

The general rules seem to be:

  • Keep it short, picking is easier.
  • Keep it open, sunlight needs to penetrate every part of the tree.
  • The best shape for the tree is an open vase
  • Keep a clean structure, spurs and cross branches cut sunlight and steal energy
  • Minimize the number of main trunks, one is best, about 36" to the first branches
  • Don't prune too often - fruit grows on last year's new growth, don't remove it all

The tools for pruning are familiar to any tree farmer. Pruning shears are used for the tiny branches inside the canopy. Loppers or pole saws can be used to control the height. Power saws or chain saws can be used to modify the structure. Olive wood is very hard; I have found that a power pruning shear saves hours and alleviates sore hands.


Olive trees are beautiful landscaping plants that magically provide some of nature's most healthful produce. They grow easily in San Diego County and are already abundant in the Ramona Valley. A little planning and proper care can turn the difficult corners of your property into attractive and productive agricultural land. Plant a tree, save the planet - one splash of olive oil at a time.