Growing Olive Trees
|August 6, 2011||Posted by admin under Trees|
Branch of peace, crown of victorious athletes, oil to light the world’s lamps and anoint the world’s holy people, and a primary ingredient in the healthful Mediterranean diet. What other reason do you need to plant an olive tree? Think of its cured, savory fruit – great for eating out of hand or suffusing a cooked dish with flavor – and you’re convinced.
You do need a few things to grow Olea europaea. First and foremost, you need the right climate, and unfortunately many parts of this country just don’t provide the long, hot summers, slight winter chill, and ample sun to bring this tree to fruition. But if you are among the fortunate who have a quasi-Mediterranean climate (think Texas, Arizona, California) you must grow an olive tree.
The olive tree is an evergreen with gray-green leaves and small, fragrant white flowers in the spring. During its youth its bark is smooth and gray, but in its venerable years it takes on a magnificent, gnarled appearance. A mature tree, depending on its variety, can reach heights of 25 to 30 feet and live for hundreds of years, even a thousand.
The olive will grow in nutrient-poor soil. But to obtain a good yield of fruit the tree must be cared for. Keep this old adage in mind: The olive tree is generous to the generous cultivator. Olives will grow well in well-drained soil with a pH up to 8.5. Give it full sun for ample fruit production; it also requires a slight winter chill to set fruit, but temperatures lower than 15°F will kill a young tree (Olive trees are hardy to Zone 8). When planting a tree, mix some lime into the planting hole. Remove a few of the branches and don’t forget to water it in well.
While the tree can survive in a hot, dry climate (olives have small leaves with a protective cuticle and hairy undersurface that slows transpiration), inadequate water will result in smaller fruit with less oil; later in the season there will be fruit drop. In the summer, water deeply but infrequently. In the winter, watering should be more substantial, but don’t overwater – this is a tree that can withstand drought and overwatering can promote root disorders.
Unpruned, an olive tree tends to grow dense with thin branches. Train a young tree to have an open-centered form that allows sunlight to reach all the primary branches. Remove watersprouts and suckers but avoid making any severe cuts until the tree has been in the ground for three to five years and is bearing fruit. Prune a mature tree to develop good secondary branches.
When you have a heavy set of fruit – more than three to five fruit clusters per foot – you may want to hand pick some fruit. You can also prune out stems with fruit, though this may remove too may leaves. However, if summers are dry and you cannot provide adequate water to the tree, prune some stems to reduce the number of leaves and thereby the competition of fruit and leaves for water. It’s a good idea to sterilize your pruning tools between cuts, especially if there is any evidence of disease. Prune away frost damage in the early summer.
Olives ripen through the autumn and into the winter. Their color changes as their oil content increases, and the color moves from green to violet to nearly black. At this time, the tree still requires water and nutrients. Green table olives are harvested first, often gathered unripe. Harvesting methods range from hand picking – the method for backyard gardeners – to gathering the fruit with a special wooden rake-like device, to striking branches and foliage with long poles to cause the olives to fall on nets spread on the ground.
Some of the olive tree varieties available in the United States are Sevillano, Ascolano, Barouni, Manzanillo, and Mission. Resistance to cold is a trait of some olive trees, so if you live in an area with marginal winter temperatures, look for a variety that’s resistant.
Olives are rarely treated with pesticides because the oil in olives retains some of the chemical residue and smell. Verticillium wilt is a fungal disease that does affect California growers. Treatment involves removing damaged trees and branches; prevention is crucial, i.e., avoid planting in infested soil. The Mediterranean fruit fly and the olive fruit fly are the primary pests that affect trees in the Mediterranean.
A few notes of caution regarding olive trees. The trees produce a large amount of pollen (they are wind pollinated) that may bother people with allergies. And, the trees may produce a fair mess when dropping fruit. The purple fruit and oil can stain concrete and litter lawns. Carefully consider your site when planting a tree. This is a magnificent, long-lived tree that will provide you with years of beauty and fruit.