Olive Care Guide

The olive tree is a round-headed, subtropical evergreen that thrives in mild winters. It grows to about 20 feet tall outdoors in USDA Zones 8-9. Thought to originate from the Mediterranean region, olives have been cultivated since around 3000 B.C. The tree can be grown in a greenhouse or container. Its fruit is used to produce oil or can be cured. The olive tree is one of the longest-living cultivated fruit trees, second only to the mango.

The tree has a rounded shape and numerous branches that bend downward, giving it a thick, bushy appearance. In very old trees, the trunk—particularly near the base—often appears as multiple trunks fused together. The leaves are evergreen, leathery, and have a dusty, ash-like appearance. In natural conditions, the tree can grow to about 30 feet tall.

The olive tree is hardier than most other evergreen fruit trees, with the exception of loquat, feijoa, and citrange. A healthy, well-nourished olive tree can recover well from frost damage, even if the wood has been significantly affected. However, it may struggle to recover if it has been weakened by heavy fruit-bearing the previous season. In general, temperatures below 14°F (-10°C) may cause serious injury to a mature tree, but temperatures around 16°F (-9°C) usually do no harm (except to young trees). The flowers and young shoots are tender, but as the tree blooms in summer, these are not affected by frost.

Olive trees are more tolerant of transplanting than most evergreen trees. Though they can grow and bear fruit on poor, shallow soil, they produce more fruit when planted in good soil. A well-draining sandy loam is ideal, and the tree should be placed in a sunny spot, either in a large pot or in a greenhouse border.

After the first year, select four or five shoots on the stem and remove the rest. Cut the selected shoots back to about 6 inches. The following year, thin out the shoots that grow from these and select a few to keep, trimming them back. This process should be repeated for three years to develop a young tree with a symmetrical, spreading canopy. In later years, you only need to thin out crossing branches to ensure light reaches all parts of the tree. To control the tree's size, branches can be shortened.

Olive trees require a cool period in winter to promote good flowering. Temperatures should drop below 40°F (4°C).

The creamy-white flowers appear in early summer in short panicles in the axils of the leaves. These flowers can be either perfect (containing both male and female parts) or male-only (containing only pollen-producing parts). The wind carries the abundant pollen, which is essential for pollination. Some humidity during the blooming period helps ensure good fruit set.

While olive trees can bear fruit in areas with low annual rainfall, they produce better crops in regions with adequate rainfall. If growing an olive tree in a pot, ensure it receives enough water, especially if the temperature in the greenhouse is high and the air is dry, which could lead to premature fruit drop.

In warm, sunny climates, the oil content and fruit weight typically peak 6-8 months after flowering. However, the olives can remain on the tree longer if they are to be used for oil. As they ripen, the fruit color changes from green to straw, rosy pink, red, and eventually black.

For oil production, olives should be harvested once they turn black. For pickling, olives are gathered while still green. Care must be taken during harvesting to avoid bruising. All raw olives are bitter, but this can be removed by soaking them in a solution of 2 oz sodium hydroxide per gallon of water until their color begins to change. Afterward, rinse the olives in fresh water for 2-3 days to remove the alkali solution, then place them in brine.

Source: Simmons, Growing Unusual Fruits