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Climate limits viability of olives as a local crop

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Olives originated in the lands that are known today as Turkey, Syria, Lebanon, Palestine and Israel. They were subsequently planted in other parts of the Mediterranean basin and cultivation in the Mediterranean region can be traced back 5,000 to 6,000 years. The olive was also important to the Greeks and the Romans, who made it a part of their mythologies to celebrate the use of its oil as an essential food and fuel for lamps. Italy and Spain since brought it into widespread cultivation. The Spanish imported the olive to the New World where early missionaries spread the olive to Mexico, California and South America.

The olive [Olea euro-paea] is a small, evergreen tree in the family Oleaceae. The tree and its fruit give its name to the plant family, which also includes species such as lilacs, jasmine, Forsythia and ash trees. The olive has oblong, silvery green leaves and the trunk is typically gnarled and twisted. In recent years, there has been a resurgence of interest in olive oil as an ingredient to flavor gourmet food and as a healthier alternative to other forms of fats and oils in the U.S. diet. Research supports the healthy benefits of consuming olives and olive oil. Currently, about 8 percent of all fats and oils consumed in the United States is olive oil. Olives are also being considered for use as a renewable energy source using waste from oil production.

U.S. olive production is greatest in California, but they produce less than 1 percent of the world's olives. Much of the current interest in olives is directed at making high quality, gourmet olive oils and specialty table olives which can be sold for premium prices. California olive growers have also begun to cope with pest issues like the olive fruit fly.

As for potential for growing olives in the Verde Valley, our climate may be the most limiting factor. Temperature controls olive tree growth, reproduction, and survival of the olive. Growth begins after mean temperatures warm to 70 degrees in the spring and continues until temperatures drop below this point in the fall. Unlike deciduous fruit trees, the olive does not set fruiting buds in the fall. Instead, the olive will only set flower buds after being exposed to cool night and warm day temperatures during the winter [called vernalization].

The olive can also freeze from extreme cold. Although the olive is the most cold-hardy of the subtropical fruit trees, it will sustain damage to leaves and small stems at 17 degrees and more severe damage at 12 degrees. The tree can be killed to the ground with temperatures below 10 degrees. Mature trees can regrow from underground parts following a severe freeze. This puts the Verde Valley in the danger zone as temperatures can dip below 10 degrees even in the warmer upland "banana belt" we know as Jerome.

Under ideal growing conditions, the olive will begin to bear fruit at about 5 years of age. Fruit is borne on branches from the previous season's growth. Two types of flowers arise on the tree: perfect and staminate. Staminate flowers contain only male parts; the pistil is aborted. Only perfect flowers can become fruits. Olive trees are largely wind-pollinated and most olive varieties are self-fertile, but increased production often results from cross-pollination. In ornamental landscapes, olive trees are often sprayed with growth regulators to reduce the number of fruits which cart become a feat mess near paved areas. The critical timing and expense of spraying led the landscape industry to develop fruitless varieties of olive trees the most popular being the Swan Hill Olive.

As for the future of olive production in the Verde Valley, time will tell. I know of some small trees but am not sure of the varieties used. Similarly, I am not aware of any experimental variety trials. Before we go much further, this baseline work should be done to determine future viability. For those interested in more history, an Extension colleague in California, Paul Vossen, has written an excellent article that can be accessed at ucce.ucdavis.edu/files/file library/5574/42140.pdf.

Follow the Backyard Gardener on Twitter use the link on the BYG website [see link below]. If you have other gardening questions, call the Master Gardener line in the Cottonwood office at 646-9113, ext. 14, or e-mail us at cotton-woodmg@yahoo.com and be sure to include your name, address and phone number. Find past Backyard Gardener columns or provide feedback at the Backyard Gardener website: http://cals. arizona. edu/yavapai/anr/hort/byg/.

Jeff Schalau is an associate agent for the Agriculture & Natural Resources Department, University of Arizona Cooperative Extension, Yavapai County.



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