How to Grow Olives
The olive (Olea europaea) is a small tree native to the coastal Mediterranean region, where it has been grown for at least 5500 years. Trees can be extraordinarily ancient - some have been authenticated as reaching 1500 years old.
The attractive tree has silver, elliptical leaves and small, whitish, fragrant flowers. Once established, it is highly drought-resistant and tolerant of poor, infertile soils. With the increasing interest in Mediterranean food and garden design has come a demand for home-grown olives. There are also many plantations now producing high-quality olive oil in Australia.
Planning the crop
Olives need a warm, sheltered situation in full sun. However, they will usually only produce flowers when at least two months during the year have average temperatures below 10 degrees centigrade. They also need a 12 to 15 week period during which there are fluctuations between day and night temperatures. This means that olives can be grown with reasonable success in open gardens and farms in many parts of Australia, South Africa and New Zealand. For olives to set fruit, a warm to hot summer is necessary. You can purchase young olive trees and bushes from many nurseries and garden centres, by mail order or via the internet. Ask for plants for fruit harvest, not for oil production. The trees don't begin fruiting until they are about five years old, so the larger the specimen, the sooner it will produce fruit.
Invariably, olive trees and bushes are container-grown, so you can plant them at any time of the year when the weather is suitable. It is best, however, to plant in late winter to early spring to allow the tree to become established before the cold weather sets in. A semi-mature tree grown in the ground will have quite a large spread, and this should be taken into account when deciding where to plant. One option is to plant olives in large tubs or containers. They do well in this situation and the effect is both ornamental and fashionable. You could also consider planting a small olive grove as a garden feature, particularly if you have the space and you live in a Mediterranean-climate area. The olive tree's silver foliage and drought resistance make it ideal for regions with hot, dry summers.
Olives require a well-drained soil that is not overly rich; keep compost use fairly restricted. They prefer a limey soil, so a top dressing of garden lime, according to the degree of acidity, should be applied to soils with a pH of less than 6.5.
How Many to Grow: Young olive trees are quite expensive, so your budget might govern how many to grow. It's a good idea to start with one or two trees or bushes. You can always buy more if these are a success. Most varieties are self-fertilising.
Varieties: Recommended varieties for fruit, not oil, are Manzanillo, Mission, Kalamata and Sevillano. All are self-fertile.
To plant, dig a hole large enough to accommodate the root ball and fill with water. Also water the pot containing the olive tree thoroughly. When the water has drained from the hole, plant the tree firmly. Ensure that the root ball and stem are set at the same depth in the soil as they were in the pot. The trunk or stem should be staked up to the crown to keep it straight and prevent wind rock. Keep the tree well watered, adding a liquid feed once a week, until it is established.
Top-dress with a pelleted slow-release organic fertiliser every year in spring. To obtain high-quality fruit, train the young trees to an open vase shape for good air circulation and sun access. Do this in summer. First remove the central leader. Then choose five strong, well-placed branches to form the tree's scaffold; remove any other branches. Once the vase shape is established, pruning is subsequently only carried out every winter to remove damaged wood and branches that are rubbing against each other.
Growing in a pot: If you choose to grow a tree in a large pot, fill it with a free-draining mix of loam and compost. Each year in spring, remove the top few centimetres and replace with a fresh mix. Regular liquid feeding, from spring to late summer, is essential for pot grown olive trees if they are to produce fruit regularly.
Pests and Diseases
An olive tree that is grown in good conditions is rarely troubled with pests and diseases. Pot-grown olives may be attacked by scale insects at times. Verticillium wilt can sometimes affect olive trees. To avoid this disease occurring, it's always worth checking with your supplier that the tree you are buying has been grafted onto a verticillium-resistant rootstock.
Harvesting and Storing
Commercially grown olives are either harvested in early autumn, while they are still green, or they are left on the tree until winter, by which time they turn purple. The green fruit has to undergo a chemical treatment process to remove the worst of the bitterness before being bottled in brine. Olives turn purple when fully ripe. They don't need to be treated with chemicals, so you can pickle your ripe olives in brine to make your own homemade preserved black olives.