Planting & Growing Info
It is important to choose olive varietals which will give the grower the highest possible yields and financial returns. In much of the Mediterranean, local cultivar traditions are extremely well-rooted and few growers choose cultivars not traditionally grown in their region.
Mediterranean growers choose their cultivars according to four main criteria:
1. Disease resistance
2. Regional traditions
3. Final product desired
In California the main criteria are:
1. Final product desired
3. Disease resistance
One of the most important of these criteria for past and present varietal selection in the Mediterranean is the prevalence of diseases within a region. For example, if you are wanting an olive for oil production and you know that wood borers and peacock spot are rampant in your region, then you might choose other than Frantoio and Pendolino.
The beauty of this for the US grower is that olive diseases are limited and are relatively easily controlled through applications of the relevant deterrent. Also, local varietal traditions have not been set within the US olive industry. This means that the US growers are presently going to choose their cultivars according to the latter two criteria of "Final product desired" and "Climate".
The FINAL PRODUCT DESIRED is often decided by the demands of local and/or export markets. Initially, growers must decide whether they want to produce olives for oil alone, table fruit alone or for both oil and table fruit. The most commonly selected dual purpose cultivars in California are Manzanillo, Sevillano and Mission. It should be noted that Kalamata gives an excellent quality oil however it is rarely processed for oil due to the high price available on the fresh fruit market. All three of these varietals are well suited to pickling and also have oil contents high enough to make commercial oil extraction worthwhile. In addition, Frantoio olives are primarily for high class oil but many growers like the nutty flavor of the pickled fruit.
The cultivars Frantoio, Leccino and Maurino contain a high percentage of quality oil and are the most commonly selected for California groves specializing in olive oil production. Picholine and Arbequina are also popular olive oil cultivars and are also available from the Santa Cruz Olive Tree Nursery.
If the grower decides on table fruit production then cultivars are chosen by their yield, size of fruit and suitability for commercial processing methods. Commercial table fruit processing is most efficient if the cultivar has a flesh-to-pit ratio greater than 6:1 (ie 6 parts flesh to 1 part pit), and the flesh has a firm texture. If black table olives are the desired product then the grower must also look for a cultivar with a relatively even ripening stage for the majority of the crop. The other (less healthful) option is to process green olives using sodium hydroxide lye processing to artificially turn the olives black.
Cultivars such as Manzanillo, Hojiblanca, Kalamata, Sevillano (Queen of Spain), and Ascolano are all known for their excellent textures and flavors when processed as table olives. As California and southern Spain well testify, Manzanillo is ranked as the world's number one table olive. Its cropping ability, disease resistance, texture and flavor combine to place it at the peak of medium sized table olives, and its medium/high oil content also makes it a valuable oil cultivar.
The second and equally important criteria is the CLIMATE in which the grove is to be established. Due to the olive tree's hardiness and adaptability, the majority of varietals can survive in just about any climate except the tropics and the poles. They have an inbuilt ability to withstand droughts and physical damage which would be the certain death of most other trees. However, it must be noted that olives will often survive in a harsh climatic zone at the expense of the crop. This is naturally unsuitable for a commercial grove and highlights the importance of climatic suitability of cultivars. From a commercial point of view, where the grower wants healthy, low maintenance trees and regular, heavy crops, climate must not be overlooked.
The following list divides California's most commonly planted cultivars into three climatic categories based solely around temperature. Although variables such as rainfall seasons and preferred soil types can effect individual cultivars in different ways, little is known of these effects under US conditions outside of California. Some cultivars will crop well in a range of climates and are listed as such below. This list is based on both Californian and international research available to date but cannot be considered conclusive as some of the cultivars have not been trialled in all climates. (cultivars alphabetically listed)
Cold Climates - Areas where temperatures can fall below 18 deg F and snow may fall occasionally. These regions generally only grow oil olives as they are less prone to heavy frost damage. A brief International Olive Oil Council summary of the cold hardiness of olives follows.
"The olive can withstand low temperatures of 18 deg F or even14 deg F, and even lower as long as it is not subjected to them for many hours, thawing proceeds slowly and the tree is not at the active growing period [March - October in California]. During the vegetative stage, the olive tree is sensitive to low temperatures which can cause damage to twigs and secondary branches, and even to the trunk and scaffold branches. Resistance to cold is a varietal trait. To ensure it fruits well, the olive does, however, need temperatures close to 32 deg F which induce vegetative rest. It withstands high summer temperatures well, and even lack of ground moisture, although it then adjusts its growing activity to an essential minimum."
The cultivars in California most commonly selected for these cold climates are Frantoio
Maurino, Leccino, Arbequina, Pendolino and Coratina (additional Californian research has also shown Barouni and Sevillano as quite resistant to cold.).
Moderate Climates - Areas where minimum winter temperatures are generally 25 deg F to 27 deg and very rarely go below 21 deg F. Such areas are considered to be typical of the world's olive growing regions. These areas provide the necessary winter chill requirements for dormancy without being so cold as to possibly damage any late season crop.
Most cultivars available in US are believed to be viable in such areas. They include Arbequina, Barnea, Barouni, Frantoio, Hojiblanca, Kalamata, Leccino, Manzanillo, Moraiolo, Nevadillo Blanco, Picual and Sevillano (Queen of Spain),
Warm Climates - Areas which have an average daily temperature in Jan of 54 deg F or less but rarely frost or fall below 28 to 32 deg F. Areas warmer than this are generally considered unsuitable or marginal for commercial olive groves as they do not allow the trees to rest during winter and thereby reduce their ability to flower and set fruit in Spring.
The cultivars believed to be most suitable for these warm areas include Barouni, Frantoio, Kalamata, Manzanillo. Nevadillo Blanco and Arbequina are also showing good crops in warm winter areas.
NB. There are additional varieties suited to each of the above climates but very little commercial information is known on many of them at this time