*Olive trees make beautiful ornamental specimens like this one in Northern California.
Gardeners and homeowsers in warmer parts of the southeastern United States are beginning to appreciate and plant olive trees as ornamentals and for shade. This is one of Steve's recently plant 'Mission' olive trees.
Olive trees are broad leaved evergreen trees grown for their fruits which are used for food and oil. They also are grown as ornamentals. Mature trees form a rounded crown which becomes irregular as they age. Olives can get up to 30 ft (9 m) tall with a crown spread about the same. The lance shaped leaves are leathery, grayish green above and silvery beneath. They are around 2-3 in (5-7.5 cm) long and borne opposite one another along the branches. The tiny creamy white flowers are carried in panicles about 2 in (5 cm) long, each cluster stemming from a leaf axil. The flowers are sweetly fragrant, blooming in mid spring, and giving rise to fruits (technically drupes) which are picked either unripe (green) or ripe (black) for human consumption.
It’s no surprise that thousands of cultivars have been named for a crop that has been grown for thousands of years over a region encompassing thousands of hectares. Among olive varieties favored for their oil, ‘Piqual’ is probably the most common variety grown in Andalusia, Spain, where most of the world’s olive oil is produced. ‘Koroneiko’ is an important oil variety in Greece. Important table olives include ‘Manzanilla’ in Spain and ‘Kalamata’ in Greece. ‘Mission’, popular in the U.S., was named for the Spanish missions in southern California where it was first planted in the late 1700s.
There are some 20 species in the genus Olea. All are evergreen and some attain only shrub stature. The genus is restricted to the Eastern Hemisphere, in northern Africa, the Mediterranean region, central Asia and in Australasia. Olea europaea (the only species cultivated for food) is native to dry, often rocky areas around the Mediterranean Sea. Olives have been cultivated in the Middle East since at least 3000 years before Christ. They are grown commercially in every country that surrounds the Mediterranean. Olives also are grown commercially in parts of South America, South Africa, Australia and interior California. In recent years olive groves have been planted in the southeastern U.S. Olives have escaped cultivation in many places where the climate is ideal for them and in some parts of California the species is considered an invasive weed.
*In Napa Valley, California this trees in this commercial olive grove are interplanted with wine grapes.
*Olives are mechanically harvested in commercial grooves and the fruit transported to the processing center via trains of large containers.
Most varieties of olive require a certain amount of winter chilling before they will bloom. Usually some 10-15 weeks of nighttime temperatures below around 40°F (4°C) will suffice. After that, they need a long, hot growing season. Light: Olive trees need full sun. Moisture: Olive trees need a very sharply drained, fertile soil, such as a loamy sand or sandy loam. They are quite drought tolerant. However, the trees produce more and larger olives if watered during the summer while the olives are developing. Hardiness: USDA Zones 8-10. Most olive varieties are killed by temperatures below about 12°F (-11°C). In general, most varieties require a frost-free climate with a cool winter and a long, hot summer. Propagation: Young, fast growing stem tip cuttings taken in early summer can be started in sand under mist. It is also possible to start new plants from suckers dug from around the base of the tree. Seeds may be sown in spring. Cultivars can be grafted onto seedling root stocks.
Olive trees are long lived slow growers and useful as visual screens. They often are planted as ornamentals and especially as street trees for their picturesque shapes, attractive gnarled and twisted trunks, and evergreen silver-backed leaves. Position olives in mixed evergreen borders or as specimen trees. If you wish to produce fruit or oil, be advised that some olive varieties are self-pollinating, whereas others require another variety for fertilization. The conventional wisdom is that slow growing olive trees take up to 10 years to begin producing, but recently I bought two young trees (a ‘Mission’ and an ‘Arbequina’) that flowered in their first year in the ground, just three years after they were started from cuttings.
Artisans prize olive wood for carving and turning.
This newly planted 'Arbequina' olive tree is blooming already.
Most supermarkets now carry a selection of olives that are differently cured, seasoned, stuffed in both green and black.
Only in recent years have olive trees been widely available to amateur gardeners in the southeastern U.S. The jury is still out regarding how well they will do in a climate sometimes too wet, sometimes too cold, and sometimes not chilly for a long enough period, but early reports are encouraging for southern gardeners. Varieties believed to be best for semi-tropical and sub-tropical climates include ‘Mission’, ‘Arbequina’, and ‘Manzanillo’, all of which are self-pollinating.
Olive fruits are very bitter and cannot be eaten until prolonged washing and soaking in salt water or (typically) a lye (sodium hydroxide) or wood ash solution which, of course, must then be removed by another thorough washing and rinsing. Olives (green or black) thus treated can be stored in a brine solution. Olive oil is made from crushing the fully ripened fruits and is not brined or lyed, the bitter glucosides separating from the oil naturally during the pressing process.
Here is a recipe for lye-curing green olives at home: Dissolve a tablespoonful (15 ml) of lye (purchased in the cleanser section of the grocery store) in a quart (0.9 L) of water and let stand for an hour or so before pouring the solution over green olives in a glass container. Let the olives soak for about 24 hours or until the lye solution has reached the pits (cut into a large olive to examine), and the olives have turned from a bright green to a yellowish green. Next, soak the olives in clean water, changing it three or more times a day for three or four days until all trace of the lye taste is gone. The olives may now be stored in the refrigerator in a solution of 6 tablespoons (89 ml)of salt per gallon (3.8 L)of water.
One of the most important uses for olives is, of course, in cocktails, and martini lovers everywhere celebrate the invention of the mechanical olive pitter in California in the 1930s.
Lye is very alkaline, the opposite of acidic. It is caustic and can “burn” the skin. Keep some vinegar handy to neutralize any lye that might splash on your skin. If lye gets into your eyes, rinse them under running water and call your doctor.