OPTIMUM CLIMATE AND OLIVE VARIETIES
Olive trees require a Mediterranean-like climate to survive. They need a long, hot summer and a cool, not frigid, winter. A mature tree can survive temperatures down to 15 degrees Fahrenheit for a limited amount of time; sustained cold below 15 degrees can be fatal. There are olive trees that survive outside of the typical Mediterranean zone but generally they do not produce economically viable crop levels.
There are many growing regions that are appropriate for olives, although each microclimate should be considered thoroughly before planting occurs. In particular, tree growers in locales that are on the edge of a good territory can have a more restrictive palate of trees from which to choose. In regions where the summers are cool or short, it is safer to choose early-ripening varieties that will accumulate enough oil in the fewer months of heat. Growers with colder winters should look for cultivars that come originally from mountainous or cooler regions. Growers who are very close to the ocean or who experience a great deal of fog should lean away from varieties that are susceptible to leaf fungal infections. The IOC’s World Catalogue of Olive Varietals is one resource for this information as are other growers in your immediate vicinity who may have local insight.
Once you have concluded that you have a good climate to plant, you must decide what type of olive to plant. There are hundreds of olive varieties in this world, but only a fraction of this total are in commercial production.
SELECTING A VARIETY
Consider whether the fruit is for oil or for table olives (or both); what is the desired flavor profile; what style of cured olive is desired; whether the aesthetic value is most important; whether there are climate constraints. Any olive can be crushed to release its oil or cured to make table fruit. Olive trees bred specifically for oil production tend to have smaller fruit with higher oil content, while those bred for table production tend to be larger, have firmer flesh, and may be freestone. There are many olive trees that produce fruit suitable for both.
If you plan to make olive oil from your fruit, taste as many oils as you can to determine what flavor oil you prefer. Your oil’s ultimate flavor profile will be determined partially by your variety choices (other factors will include harvest date, irrigation management, fertilization, type of mill, etc.). Some varieties will produce mild tasting oil, others fruity, pungent, or floral oils. Visit our Tuscan Olive Varietals page for more information.
You will also want to ensure that you are within reasonable driving distance of an olive mill that can process your fruit. There are many mills within the western US that process outside fruit, including McEvoy Ranch. Lists of milling services are also published on the California Olive Oil Council website and the Olive Oil Source website. For information about expected olive oil yield, please refer to this article.
FOR CURED OLIVES
Any olive can be picked early to make green olives or can be picked later, when the fruit is more ripe, to make black olives. Some varieties are better suited to green olives or black olives, but, given enough time in the season, any tree will produce both.
The large number of olive tree varieties is only bested by the number of curing recipes. Recipes range from the lye process (utilized by the California canned olive industry), to a simple brine (salt water), to dry salt packs. The internet (other than a family member’s recipe box) is the best resource for good olive curing recipes. The McEvoy Ranch chefs use a simple recipe published in Gerald Gass’ cookbook, The Olive Harvest Cookbook. Safe canning procedures should be followed to avoid botulism. UC Davis’ essay Olives: Safe Methods for Home Pickling is a good source of information.
Olive trees are wonderful additions to the landscape with their silvery-green foliage and evergreen canopy. Unwanted fruit, however, can make a mess when it is not tended. If you are purely interested in the aesthetics of the tree, it is better to plant a fruitless varietal. Be forewarned that many “fruitless” varietals turn out to be more prolific than advertised; if you are dead-set against having olives, then look for another type of tree.
If you have a tree that produces fruit that you do not want, you have a few options. There is a commercially available spray that will desiccate the blossoms to prevent fruit set, but this product is not organic. The only organic option (save for removing the tree altogether) is to spray the flowers with a high-pressure hose while they are in bloom. It will take more than one spray over the course of the blooming season to ensure that all the flowers have been damaged enough to arrest fruit set. An easier option is to change your mind about the fruit, start taking care of the tree, and harvest your fruit for tasty oil or cured olives!