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Marin's Mediterranean climate ideal for growing olives

  • Barbara J. Euser

    The Mediterranean climate of Marin County is ideal for cultivating olive trees. A number of commercial olive farms have taken root in our county. But any household garden may have enough room for one olive tree — and that is all you need. The commercial growers cultivate trees that produce olives for oil. The backyard gardener wants to produce olives for the table.

    Several years ago, growing olive trees seemed mysterious to me. Now I have been overseeing my own olive farm in Greece with 120 trees for four years and growing olive trees seems much simpler. On my farm, 60 trees are Koroneiki, small trees that produce small olives with relatively large pits, unsuitable for the table but producing high quality oil. Thirty-eight trees are Athenas, large trees that produce medium-sized olives suitable for either oil or the table. I have two trees that produce olives specifically for the table: one Kalamata and one Chalkidiki, also called Gaidero or "donkey olive." Kalamata olives are large black olives generally preserved so they remain rather salty. Gaideros are giant green olives, often served stuffed with garlic or almonds or blue cheese. My advice to the backyard gardener would be to choose one of these two varieties or if your yard is large enough, one of each.

    Olive trees are extremely hardy. They do not require additional water once established. Olive trees naturally produce large crops one year and minimum crops the next. However, by watering your olive trees during the dry summer season, you can encourage them to produce large crops each year. Even young trees produce some olives. It is thrilling to eat olives from your own tree, even one jarful.

    Olive trees should be fertilized once a year in January. If you want to produce a maximum yield every year, you can fertilize your trees more often. My olive farm is certified organic by DIO, one of the EU certification organizations. Thus, I use only organic fertilizer on my trees.

    Olives are susceptible to the Mediterranean fruit fly. Unfortunately, this pest lives in Marin County as well as in the Mediterranean. A bag containing an organically approved mixture of pyrethroids, hydrolyzed proteins, ammonium bicarbonate and other substances may be hung on the branches of the tree to repel the flies. The contents of the bag last for about three months, so it should be hung on the tree in August, and it will last until harvest in October. The flies lay an egg under the skin of the developing olive and as the hatched maggot grows, it eats the olive. If a fly does lay an egg in an olive, you can see a mark at the entrance hole. Those olives must be discarded, as they are not fit for the table.

    Commercial olive growers also protect their trees against attack by the fruit flies because the infected olives raise the acidity level of the oil. The best quality olive oil has a low acidity level, indicating minimal impurities in the oil.

    Processing olives for the table is a labor-intensive job: table olives must be picked by hand. Then before they are put into salt water to preserve them, they must be sorted through to eliminate fly-infested or otherwise damaged fruit. Giant Gaidero olives should be slit on three sides with a paring knife, so that the brine will penetrate the olives. Kalamatas may be slit if you desire, but it's not imperative. Put the olives in a large jar and fill the jar with water. Raw olives are extremely bitter and inedible. To leech the bitterness out of olives, change the water every 24 hours until the olives are no longer bitter. Then place the olives in saltwater. The level of salt in the water is easy to determine: float a raw egg in its shell in the salt water. You have added enough salt when about one-third of the egg is above water. Remove the egg.

    The olives can remain in salt water until you decide to eat them, up to a year or more. When you do decide to eat them, there are many different ways to prepare them. But first you need to taste one. If it is too salty, you can leech out the salt by putting the olive in fresh water overnight. Taste another one. If still too salty, change the water and taste one the next day.

    Once the olives have a nice flavor, rinse them in fresh water and cover them in olive oil. You may add some red wine vinegar to the oil to sharpen the flavor. Or add slivers of garlic to the oil. The olives will be infused with garlic flavor. Try adding hot peppers to create spicy olives. Olives — either in brine or in oil — do not need to be refrigerated. If you do refrigerate them, the oil solidifies and will need to return to room temperature before you can eat the olives.

    Prepared olives can be eaten as appetizers, added to salads, used to flavor baked dishes or stews. The savory fruit is a healthful addition to any meal. You can enjoy the pleasures of growing your own table olives by planting a single tree in your own backyard.

    The University of California Marin Master Gardeners are sponsored by UC Cooperative Extension. For questions about gardening, plant pests or diseases, call 499-4204 from 9 a.m. to noon, and 1 to 4 p.m. weekdays, or bring in samples or pictures to 1682 Novato Blvd., Suite 150B, Novato.