Marin IJ Articles

Olive trees fit perfectly in Marin's Mediterranean-like climate

• Jennifer Kinion

• Olives are beautiful to behold in Marin gardens. Once established, they require little to moderate water and their gray-green foliage pairs well with other low-maintenance Mediterranean plants. Enterprising gardeners can add this signature California tree to their ornamental landscapes and also reap an annual olive crop. Harvest the fruit at the right time and take care and consideration when storing and curing the fruit, and you can look forward to serving olives at dinner parties and potlucks.

  Success with olives starts at the nursery. Some varieties you might encounter that are widely grown in home gardens include kalamata (a good choice for water curing), hojiblanca and picholine. When evaluating trees in 1-gallon nursery containers, look for ones with single trunks that are no larger than 4 to 5 feet in height. The ideal tree starts branching out at about 3 feet from the base of the container and has visible soft growth at the ends of the branches. Rule out the trees that don't exhibit active growth, as those trees might be root bound from spending too much time in their containers.

  Before you plant your tree, evaluate the site. Ensure that the tree will receive full sun. Also consider how you plan to maintain the tree's eventual size. Olive trees will ultimately reach a spread of 20 feet unless they are pruned. Consider whether the site you choose will require you to prune the tree heavily to control size and shape (which is fine, as olives do well with heavy pruning) or whether there is room for the tree to assume a taller, wider shape.

  Dig a planting hole roughly the size of the planting container, and, taking care to minimize disturbing the root ball, remove the tree from the container. Cut off any roots that encircle the root ball. When placing the tree in the hole, set it a bit higher than the surrounding soil level and fill in with the soil you dug out. Avoid adding planting mixes, compost or other amendments to the planting hole. Why? Amendments fool the developing tree into growing as if they are in a pot - root growth gets limited to the extent of the well-amended soil. Using all-native soil encourages root growth beyond the diameter of the planting hole and into the surrounding soil.

  After planting, keep the tree well watered, irrigating whenever the soil gets dry. Fertilize with compost or a high-nitrogen fertilizer after new growth appears in the spring. Keep the surrounding area weed free.

  Olives are harvested late in the year, and the degree of ripeness desired depends on what method of curing you plan to use. Green-ripe olives are harvested when fruit has reached its full size and it releases a white, creamy juice when squeezed. Turning-color olives are firm but not deeply pigmented. Those olives that are allowed to fully ripen on the tree for about three or four months after the green-ripe stage are referred to as naturally black ripe olives.

  Why should you cure your olives? They contain a compound called oleuropein, which makes the fruit inedible. To turn your crop into a food source, you must first cure them to leach out the bitter compound. Home olive producers can choose from several methods to accomplish this; some methods are targeted to a specific result with different varieties. Water-curing is often used with kalamata olives, and is a relatively quick method, typically yielding results in a few weeks. Water-curing is achieved by cracking or cutting individual olives and then soaking them in water. The water is changed each day over the course of a week or longer. After the water soak, a finish brine made with vinegar and salt is used to add flavor. Other methods of removing the oleuropein include brine-curing, dry salt-curing and lye-curing.

  Cured olives can then be preserved by storage in a heavily concentrated brine, or freezing, canning or drying. Before trying any food preservation method at home, research current recommendations and tested guidelines. The UC Division of Agriculture and Natural Resources offers a wealth of information on freezing, canning and other methods of food preservation. "Olives: Safe Methods for Home Pickling" (ANR publication No. 8267) is available for download at http://anrcatalog.ucdavis.edu.

  UCCE farm adviser Paul Vossen will discuss "Let Them Eat Olives! How to Successfully Grow and Harvest Your Own Olives in Your Back Yard" on Sept. 3 at the Marin Art & Garden Center in Ross. Vossen will discuss growing and harvesting olives in Marin, which types of trees are best for different kinds of olives, common olive pests, how to prune olive trees, and how to harvest and brine olives. After the presentation, there will be an olive tasting.

  Vossen has worked as UCCE farm adviser in Sonoma for 28 years, specializing in, among other things, fruit trees, berries and olive oil. His research on the effects of irrigation and olive fruit fly damage on olive oil's sensory qualities was instrumental in developing a newly released UC manual on organic olive production.

  IF YOU GO

  - What: "Let Them Eat Olives! How to Successfully Grow and Harvest Your Own Olives in Your Back Yard" with UCCE farm adviser Paul Vossen

  - When: 7:15 to 8:15 p.m. Sept. 3

  - Where: Livermore Room, Marin Art & Garden Center, 30 Sir Francis Drake Blvd., Ross

  - Admission: $5

  - Information: 499-4204

  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.