In a state with declining irrigation water, olives for oil could be the next big thing as those grown for oil need about 1.5 acre feet of water per season to produce a good crop. This compares to about four acre feet required for tree nuts.

Northern California’s climate is ripe for olives, according to Artois grower Dan Kennedy. Planted in hedge rows, the small trees lend themselves to mechanical management; everything from machine trimming to harvest.

Even under Northern California’s blistering summer temperatures which can easily surpass 110 degrees olives appear to grow well. Basically the critical periods for growers are the spring bloom and October harvest periods where occasional freezing temperatures can impact trees and fruit.

There were three successive winters where temperatures fell into the teens for extended periods of time in Kennedy’s orchards. When that occurs before harvest growers have about 24 hours to harvest fruit and move it to the mill. Temperatures like that between harvest and bloom, which is what happened in Kennedy’s case, freeze burned entire blocks of the Arbosana variety, leading to more aggressive pruning than otherwise necessary.

It can take a year or two for olive trees to recover from such a freeze. Generally speaking, mid-20 degree temperatures for a few hours during the dormant season are not overly concerning.

Kennedy is one of about 70 farmers growing olives for California Olive Ranch, America’s largest producer of olive oil. He farms west of Interstate 5 near Artois in the Sacramento Valley. Aside from about 650 acres of high-density olive plantings he owns in various partnerships or manages, he directly owns about 140 acres of olives and walnuts.

He also farms about 400 acres of rice. Some of the olives are planted on former rice ground. Some are planted on poor soils where corn and other crops once grew, he says.

“We didn’t bring that gravel in,” he says pointing to one olive orchard with enough gravel to pave a driveway.

Kennedy grows Arbosana, Arbequina and Koroneiki olive varieties for California Olive Ranch. Arbequina is his main variety. It's billed as more frost tolerant and a good pollinator for other cultivars which can be important as freezing weather can happen during the spring bloom and October harvest. Koroneiki seems to be more susceptible to olive knot; a disease he says doesn’t appear to be a problem in terms of yield drag or reducing the quality of the fruit.

Gregory Kelley, president and CEO of California Olive Ranch, says olives for oil respond well to a fully-mechanized management system. He says they grow well under the climate and conditions common to the North State, as that region of northern California is often referred.

“We still do some hand pruning on our orchards,” he says.

California Olive Ranch owns “thousands of acres” of olives. Kelley did not share the exact acreage COR owns which is spread across about 12 different varieties.

Since its founding in 1998, Kelley says COR has managed to boost tree size in super high-density plantings. They started with grape harvesters which limited tree size and row spacing. Since then, COR partnered with Oxbo to build larger harvesters that allow for trees up to 12-13 feet tall.

The newer harvesters are better built to withstand aggressive shaking necessary to remove olives from trees. As with blueberries, grapes and prunes, these harvesters shake fruit onto a catch frame which then transfers the fruit to a trailer in the next row pulled by a tractor.

Olive trees used in oil production are skirt pruned to allow the harvester to close in on small trunks and prevent fruit from falling to the ground.

Oxbo harvesters are domestically produced with replacement parts easily obtainable from the local auto parts store, Kelley says. While the old grape harvesters are not capable of harvesting olives in these configurations, Oxbo harvesters can double as grape harvesters.

On tree height, Kennedy says 13 feet is the limit, not only for the machines but to prevent shading adjacent rows which can be as narrow as 12 feet on trees spaced five feet apart. Next year, they will experiment with rows 10 feet wide meaning about 1,400 trees per acre. Current tree densities can vary between a few hundred trees per acre to more than 700.

He says olives in the North State are typically planted on a north-south configuration due to the sun and to allow the prevailing wind to aid in pollination.

Relatively new planting style

Though olives themselves are not new to the North State, they came in with the early settlers who planted trees in hedgerow configurations for oil production which has been an evolving process, according to Kennedy. He has trees planted in rows that vary slightly in width and distance between the trees.

Kelley says COR owns the oldest super high-density orchard in the U.S.. The orchard is 18 years old and “still producing quite well.” Orchards are planted with a 25 year expectancy, but real tree longevity is not truly known.

Kelley does not know how long olives can produce in this configuration which typically includes a two-wire trellis system and metal poles. The system helps train the young trees which are propagated from seeds at a nursery and not grafted to rootstock. The trellis also proves tree stability in wind.

Kennedy says early plantings were managed to grow trees as fast as possible to the top of the six-foot bamboo the small trees were tethered to. Now the idea is to grow trees slower with the hope they will still produce by year three and hit full stride by year five.

“Sometimes you’ll see a big crop on year three which was more than you thought you’d get,” Kennedy says. “That will back off a bit on year four.”

Olives tend to be alternate bearing which sets fruit on two-year-old wood for bloom and production in year three. Well-managed olive orchards can contain alternate-bearing yields to plus or minus 20 percent of the mean, the olive grower says.

Growing olives for oil is less of an issue of fruit tonnage and more about gallons of oil per acre, Kelley says. Weather and nutritional programs can play a significant role in oil volume and quality.

Tighter densities?

Kennedy intends to further increase orchard density with new plantings. Row spacing will be 12-feet wide with five feet between trees. This is one foot narrower and shorter down the rows than recently planted orchards, adding another 180 trees per acre. Orchards will remain planted on single-line drip irrigation with emitters spaced every three feet. Irrigation rates are about a half gallon per hour.

Lizandro Magana is COR's agricultural operations manager. As part of his roll to oversee all COR olive orchards, he is working with a 5x13 spacing on a single-wire trellis that plants trees a little more developed than in previous plantings with 670 trees per acre. This allows trees to go between 30-36 inches, make one last tire at the wire, cut it, then let the tree grow. The advantage is allowing the tree to set multiple fruiting positions instead of what he calls a "pine tree” that just grows straight up.

Next year, Kennedy will also experiment with a 'no trellis' planting style that uses a thicker bamboo to tie the young trees, and includes about 1,400 trees per acre.