Growing Olives

It is hard to imagine a Mediterranean garden without the beautiful gray-green leaves of the olive tree. It seems they have become as synonymous with Wine Country as the grape vines themselves, and for good reason. If you have ever sat beneath a mature olive tree on a warm summer evening, enjoying the rich flavor of cured olives with a glass of a nice fruity Syrah you know what I mean.

Where olives grow native they are an indicator species for a Mediterranean climate. Like the Napa Valley, these areas have mild winters and long, warm, dry summers. The trees are frost tolerant to 22 degrees, with minor damage occurring at this temperature. Large limbs and whole trees can be killed if temperatures fall below 15 degrees. Freezing temperatures of 24 to 26 degrees during the growing and maturation period injures Olive fruit. During the 1990 freeze in California, Manzanillo trees suffered the most extensive damage, Ascolano proved the hardiest.

Olives adapt to a wide variety of soils that allow for unrestricted root growth. They prefer finely textured soils that have a high water holding capacity and good aeration. Olive trees are shallow rooted and do not require very deep soils to produce well. Trees produce well on soils with a pH greater than 5 and less than 8.5.

Although olives are drought tolerant, trees do require supplemental irrigation during the growing season. Deep watering two or three times a year will increase fruit production. Avoid watering towards the time of fruit maturity to reduce the water content in ripe fruit.

Olive trees need full sunlight. The olive tree bears fruit on 1-year-old wood found on its outer branches exposed to adequate sunlight. Olive shoots do not flower or produce fruit in full shade.

Your trees will benefit from an annual application of compost and a small amount of a balanced fertilizer. Fertilizers high in nitrogen should be avoided as they promote excessive shoot growth and many small fruits.

For the most part, olives are easy to grow in the Napa Valley, though there are a number of pests that can affect the trees. The biggest challenge at COPIA is the Olive Fruit Fly. You can recognize the damage by the round sting marks on the skin and decimated flesh inside. To keep populations down, pick up all fruit off the ground because it will serve as an over-wintering site for the flies. Homeowners can also use an organic spray called Spinosad that, if applied weekly through the growing season, should offer very good control. You may also have some problems with scale, sooty mold or olive knot disease that produces a gall on the twigs and branches. For the latter, cut out the infected areas, sterilizing your tool between cuts.

Because olives are produced on 1-year-old shoots, the production of fruit is confined to a shell of new shoots 2 to 3 feet thick on the tree’s periphery. The most productive olive shoots are 12 to 18 inches long. Short or excessively long shoots are the least productive.

The objective of pruning is to develop new, shoots on the tree’s periphery.

Prune trees in spring and summer once the rains have passed. Pruning induces new growth so well distributed cuts on small-diameter wood will spread this stimulus over the entire tree. This type of pruning can be thought of as thinning cuts. Another type of cut that can be made are called heading cuts. These cuts are used to shape the tree and direct its growth. When trees reach a height that makes hand harvesting unsafe tall upright branches can be removed.
COPIA's Olive Collection

Mission

The Mission variety was introduced into California by seeds brought from Mexico in 1769. The tree has a definite upright form. Very old trees reach a height of 40 to 50 feet.

Many Missions bear crops only in alternate years with the crop being ready for harvest in November, later than most varieties. The Mission produces olives that are considered small for their size, but they have the highest oil content of any of the other olive grown here at COPIA.
Manzanillo

In 1875 the Manzanillo variety was brought to California from Spain. Today it has the distinction of being one of the leading table varieties. Manzanillo trees are about 15 to 30 feet tall at maturity and if not crowded, have a spreading habit of growth.

Its tendency toward regular bearing is one of the most important advantages of the Manzanillo. The fruit is medium sized and is usually ready for harvest in October or early November. The fruit contains enough oil to warrant their use for oil extraction.

Sevillano

Sevillano was brought into California about 1885. It derives its name from Sevilla, the province in Spain where it originated. Mature Sevillano trees will vary in height. Under favorable conditions they will attain a height of 25 to 35 feet, but if planted in poor soils they remain quiet small. Their spreading growth habit makes harvesting relatively easy. The trees bear erratically and are not as dependable as Manzanillo for consistent production. Fruit is harvested from mid to late October. Sevillano olives are the largest produced by any of the COPIA olive varieties. The fruits main use is for canned olives, its oil content is relatively low and is not generally processed for olive oil.

Ascolano

The Ascolano variety originated in Italy and was brought into California in 1885. It is the standard for pickling in Italy. Trees attain a height of 20 to 30 feet, and if left uncrowded, will develop a beautiful round shape. Young trees bear fairly regularly but older one tend toward being irregular bearing. The Ascolano is the earliest ripening olive at COPIA, generally ready for harvest mid-September through mid-October. The fruit is large and is used for producing colossal sized canned olives.

Geoff Palla