The lush and graceful appearance of a fully-grown olive tree is both distinctive and attractive. Against the backdrop of a green garden, the grey-green leaves of an olive tree provide an interesting contrast. These evergreen trees can live for up to 500 years and are known to regrow even when chopped to the ground. The average height of mature olive trees can reach up to 50 feet, with a spreading canopy of up to 30 feet across. With careful pruning, its spread can be kept to around 20 feet. Ripe olives usually appear within 4 years. Most olive tree varieties are self-pollinating. In addition to the care commonly given to cultivated trees, most olive trees require specialised care to ensure their health and to maintain proper growth patterns. This article pertains to species of olive trees grown in the United States.
Condition the soil in which the trees are planted. Keep the soil moist, but not soggy. Feed the soil with a high-nitrogen content fertiliser (a 17-6-10 timed release formula works well). The pH of the soil should not exceed 8.5.
Prune your olive trees properly. Always clip branches at the leaf nodes to encourage fuller growth. If only a single trunk is desired, prune away any growth below the desired branching point. If you wish to cultivate the gnarled appearance of several entwined trunks, stake basal suckers and lower branches to the desired angle and allow them to twist together. Prune upper branches only to train them to grow in the direction and shape desired.
Protect your olive trees from disease. In North America, olive trees are vulnerable to olive knot disease, which is spread by pruning with infected shears during rainy periods. In California, the fungal disease called verticillium wilt can cause major damage. Experts advise that there is no effective treatment except to remove diseased trees and branches and to avoid planting on infected soils.
Apply fertilisers systematically. In California, for example, where summers are often dry, fertilisers are added long before flowers appear on the branches so that the nitrogen can be absorbed, rather than washed away before the tree produces fruit. In Mediterranean countries (which tend to have more rain), organic fertilisers are applied only every other year.
Harvest fruit by hand. Olives are extremely fragile when ripe, and bruise very easily. If green olives are desired, pick the fruit once it has reached mature size, but still retains its green hue.
Home-grown olive trees generally benefit from a deep watering once a month, although the hardiness of these trees allows them to withstand extended dry periods. Remember when pruning that most olive trees will never bear fruit in the same place twice. Container olive trees should be kept inside during the winter in regions that may experience temperatures at or below freezing. Keep indoor plants away from the dry heat of furnaces and radiators, and place them near a window facing west or south.
Olive trees should not be sprayed with pesticides. These trees tend to have fewer issues with pests than other trees, and chemicals will transmit their odour and taste to the fruit and oil produced by the tree. If necessary, employ organic pest control as is done in the Mediterranean.