In the ongoing pursuit of new cash crops for Hawaii, some farmers are planting Mediterranean olive trees as a possibility. Several farms on Maui have planted hundreds of plants with the first full production year approaching. Though most varieties require a seasonal chill to flower and fruit, several cultivars hold production promise in the tropics when grown at upper elevations
In the ongoing pursuit of new cash crops for Hawaii, some farmers are planting Mediterranean olive trees as a possibility. Several farms on Maui have planted hundreds of plants with the first full production year approaching. Though most varieties require a seasonal chill to flower and fruit, several cultivars hold production promise in the tropics when grown at upper elevations
Aside from their production ability in Hawaii, olive trees can be planted as lovely specimen plants requiring so little care that they can be used in a xeriscape landscape. They can tolerate a variety of soil types as well as drought, hot sun and mild salt spray. Despite their shallow roots, the trees can withstand moderate wind. Olives are unlikely to fruit at lower elevations, but if they do produce fruit, you need to be prepared to harvest them. Though the tree can serve as an attractive ornamental, dropping fruit can be messy in small garden areas.
The fruit can be used in many ways depending on harvest time and processing choices. The martini olive needs to be picked early in the season and subjected to brining. Midseason harvests produce great olive oil and black olives harvested later can make wonderful salad additions or tapenades.
The European olive, Olea europaea, has become invasive in several places including Australia. It is currently listed in Hawaii’s Most Invasive Horticultural Plants. Since the best way to propagate olives is by cuttings, care with discarding cuttings can reduce spreading. Limiting access to the trees by large birds or other animals that might eat the fruit and spread the seeds into native forest areas is also needed to keep olives from becoming invasive.
Olives are native to the Mediterranean region and western Asia. A native Hawaiian olive, Nestegis sandwicensis, (olopu in Hawaiian) is in the same Oleaceae family, but it does not produce edible fruit and is not widely grown. Other species in this family that are grown as ornamentals include privet, jasmine and pikake.
Evidence of olive cultivation goes back at least 5,000 years beginning in areas around Palestine, Syria and Crete. References to olive trees, their fruit and olive oil can be found in the Bible and the Quran as well as in ancient Greek and Roman records. The Olive Tree of Vouves, on Crete, is estimated to be more than 3,000 years old and it continues to produce olives that are, needless to say, highly prized. Olive trees planted today are likely to live longer than any of us.
Olives arrived in California from Spain with the Franciscan monks and were cultivated in and around their missions. Olives became an agricultural commodity in the U.S. as early as 1871 when an olive oil mill was established in Ventura, California. Don Francisco de Paula Marin introduced olives into Hawaii in 1827 and they became naturalized in several upland locations. Today they are an established crop in California and hold the potential as an agricultural crop for Hawaii.
Several olive varieties are available locally that hold production promise for Hawaii. Arbequina is from northern Spain and produces small fruit that presses into high quality oil. The tree is usually less than 20 feet tall and can start producing fruit within four years. The semi-dwarf cultivar Arbosana is also of Spanish origin with fruit similar to Arbequina that matures about three weeks later. It is a newer cultivar with a vigorous, bushy growth habit. It produces medium-sized fruit. Another Spanish variety, Manzanilla, produces mature olives early in the season.
All of these trees are attractive and can serve as crop plants as well as ornamentals. When considering growing olives for their fruit, it is important to know that they require close to two months of cold nights in order to produce flowers and fruit. Where temperatures dip below 55 degrees in winter, fruiting is more likely.
Olives are usually pollinated by wind. Hence, they need dry conditions during their summer bloom season, usually from April to June. Extreme heat during this time can negatively affect fruiting.
Olive trees have fissured gray bark with trunks that become gnarled and twisted as they age. The oblong leaves average about 2 inches long and are a silvery green. White flowers appear in racemes out of the axils of the leaves and are usually produced on the previous year’s wood. Because of this, olives are likely to have light fruiting years following a heavy harvest. Careful pruning during heavy flowering can remedy this tendency.
The fruit of the olive tree is botanically known as a drupe and contains a single seed. Fruit can be harvested when it turns from dark green to light green or later when it is partially brown or when it is completely ripe and dark brown or purple.
Olive seeds, or pits, do not germinate easily and often do not grow true to the parent plant. The best way to propagate olives is by cuttings or layering. Once you have healthy roots on your cuttings or layers, you can plant out your tree. Choose a spot in full sun with soil that drains well. Olives hate wet roots and will not thrive in situations where the soil does not dry out between waterings. Controlled irrigation and regular fertilization, though not required, often causes an increase in fruit size and production.
Olive trees grow slowly but they can tolerate occasional pruning to maintain the desired size and shape. If you are growing for production, you may want to open up the center of the tree once it starts flowering and fruiting. Depending on variety this can be anywhere from four to 10 years after planting. Sun exposure to the interior of the tree will increase fruit production.
Diseases of olives are uncommon other than the preventable root rot. The olive fruit fly may lay its eggs on the fruit. When the larva hatch, they tunnel into the fruit making it unusable commercially. Fruit fly traps and sprays can control this insect pest. Though scale is occasionally a problem on olives, this pest is easy to control with a soap and oil combination.
Today, olives growing in the Mediterranean region are the world’s most important oil-producing crop. Beyond its appeal as a crop or even as an ornamental plant, the wood of the olive tree is an attractive hardwood. It is dense and has a fine grain that is prized for carving and for use as trim on high quality furniture.
Several area nurseries carry olive trees. Call around for availability.
Diana Duff is an organic farmer, plant adviser and consultant.