How to plant, grow and prune an olive tree

What you need to know about an olive tree

Name: olive (Olea europana cvrs)

Plant type: evergreen fruiting tree

Height: naturally up to 15m, but usually less than half this

Foliage: 5–10cm long by 2–3cm wide, stretched oval shape, tapering equally at both ends with a distinct point on the tip. Leaves vary from dark green through to silvery grey, depending on variety.

Climate: sub-tropical, warm temperate, semi-arid, cold temperate in protected and mild areas.

Soil: deep, well-drained, sandy or gravelly with moderate organic matter.

Position: full sun, tolerates strong wind including in coastal situations once established.

Flowering: flowers are tiny, less than 8mm across, borne on a long stem of multiple flowers. They are creamy coloured and quite fragrant.

Fruiting: fruit ripens in autumn to winter depending on variety and region. Most start green then ripen to a purplish-black, although some varieties are green when ripe. They are roundish-oval in shape and generally 2–3cm long, although size varies between cultivars.

Feeding: can grow without additional nutrients, but benefits from an application of controlled-release fertiliser annually. For best results, supplement occasionally with liquid seaweed or an organically-fortified liquid product.

Watering: very dry-tolerant once established. Best with natural rainfall in winter, small amounts of rain during flower and fruit set and then a dry summer as fruit develop.

Appearance and characteristics of an olive tree

Generally, a single main trunk with multiple branches spreading to form the crown, the shape of an olive tree is best described as fan or vase-like. A mature tree has a graceful, almost weeping appearance. Older trunks and branches become very ancient and gnarled in appearance.

The foliage is an awesome landscape addition as it has, overall, a very attractive silvery appearance. This is actually due to the underside of the leaves, as the tops are generally a dark green.

Olives tend to grow quite quickly when young, especially if provided with adequate moisture and regular feeding. As they age, however, their growth slows. Olives are very long-lived. Trees hundreds of years old will still produce fruit, and they can live as long as 1000 years.

They will tolerate an enormous range of climatic conditions, growing in virtually every zone. Many people are happy to grow them purely as ornamental trees, as they take very well to pruning and training. They can be used as topiary ball-on-a-stick style standards, trained flat against walls and fences as espaliered specimens, pruned as a large screen or just kept clipped and dense.

Given the right situation, they can also fruit abundantly, with a crop of 30kg of olives per mature tree quite achievable.

Plants with silver foliage are often some of the hardiest and most dry tolerant. The silver-grey, especially under the leaves, is a modification to help plants avoid excessive moisture loss in hot conditions and to prevent the leaves being scorched by glare reflected from water or bare soil. This makes many species of olive very suitable for situations of heat and reflected light, such as around swimming pools.

Uses for an olive tree

An olive tree has many useful features:

1. Produces fruit that can be preserved by pickling or salting and also pressed to make olive oil
2. Adds a Mediterranean look
3. Excellent around swimming pools
4. Performs extremely well in large pots and planters
5. Topiary and espalier forms can be shaped and trained 
6. Excellent feature tree providing good summer shade
7. Great in a low-maintenance or sustainable garden.

How to plant and grow an olive tree

Temperature and climate

Olives prefer a Mediterranean-type climate—long, hot, dry summers, which ripens the fruit, and a degree of cold and moisture across winter. To set flowers and fruit well they need a certain degree of winter chill hours (time below around 8˚C). The number of hours required varies with the variety, and ranges from around 200 hours to over 500. If you are planning to grow yours for fruit, make sure you have selected the right variety for your climate.

Olives are very intolerant of high humidity, which leaves them vulnerable to attack from a range of pests and diseases.

Sunlight

Your olive tree will grow best in full sun, although it will grow in some shade. Fruiting is reduced incrementally as shade gets heavier, and trees will become more “leggy” and less dense too.

Aspect

The olive is very tolerant of windy positions, although young trees may require staking until they are established. It will tolerate coastal conditions well, provided it does not receive a lot of direct salt spray. In cooler zones it can be positioned against a wall that receives direct sunlight in a location such as a courtyard. This can create the sort of heat trap that it will enjoy. Olives can survive frosty conditions to around –5˚C once they are established.

Soil

An olive tree will be tolerant of a very wide range of soil types and does best in what could be described as poor-quality sandy or gravelly soil. It will do well in virtually any soil, growing where many other trees will not, but is intolerant of wet, cold soil.

Water

The olive tree will be very dry-tolerant once established, and happy with natural rainfall of between 500–750mm, provided that most of this falls in winter. The best watering pattern is moderate amounts during winter, small amounts in spring during flower and fruit set, and then a dry summer as the fruit develops.

Feeding

An olive tree requires very little if any feeding once established, although it will benefit from an annual application of controlled-release fertiliser and an occasional application of a liquid seaweed product or an organically fortified liquid during flower and fruit development.

Tips for planting olive trees in the garden

Olives have an extensive surface root network, which is unusual for a dry-tolerant tree, and a deep root network. The latter is what helps it survive very dry conditions. Knowing this tells you two things: that you need to make sure the soil of the planting hole is well broken up, and that mulching after planting is essential.

Although not required, you can blend planting compost or composted manure through the planting soil, and the addition of some controlled-release fertiliser will also be beneficial.

New trees should be mulched well and staked with at least two stakes.

Caring for your olive tree

1. Protect young trees from frost for the first couple of years. This can be done by throwing a sheet of frost-blanket over the trees on the nights when frost may occur.
2. Avoid any fertilisers or composts that may be high in nitrogen, as this will adversely impact on flower and therefore fruit development.

How and when to prune an olive tree

Pruning is best done early and often. Olives are also known to only fruit biennially if not regularly pruned.

1. Prune out vigorous suckers that may occur lower down the trunk, especially if they arise below the graft.
2. Remove the tips of young shoots to encourage bushiness and contain size.
3. Olives fruit on one-year-old wood, so this regular pruning encourages the required growth.
4. Keep the framework of the tree open to reduce humidity.
5. Older or damaged trees can be heavily pruned and will reshoot readily.
6. If trees have outgrown their location they can be heavily pruned, too.

Diseases and pests that can affect an olive tree

Healthy trees growing in the right climate will be virtually problem-free. However, the following things may occur:

1. Thrips can attack leaves; this is generally identifiable by curling of leaves or silvering of top surfaces.
2. Fungal and root-rot problem can occur in situations of waterlogging.
3. Birds can strip a tree of all fruit very quickly.

How to propagate an olive tree

Store-bought olive trees will be grafted, which makes propagation difficult at home.

Growing olive trees from seed

An olive tree can be grown from seed, but it will revert back to the small-fruited wild variety. The seed needs to be gently cracked or softened through extended soaking in water before sowing into a seed-raising mix. These seedlings can be used as grafting understock.

Growing olives from cuttings

Cuttings are quite easy to take, however their root system may not be as tolerant of conditions as the grafted understock.

Hardwood

Hardwood cuttings should be taken in winter from two-year old shoots, dipped in striking hormone and placed in propagating mix, keeping the mixture moist, not wet.

Semi-hardwood

Semi-hardwood tip cuttings can be taken in spring and summer, dipped in striking hormone, placed in propagating mix and kept moist through misting.

Trunk sucker shoots

Trunk sucker shoots (from above the graft) will root readily if removed and placed into propagating mix and kept moist.

Safety tip

If using products to deal with pests, diseases or weeds, always read the label, follow the instructions carefully and wear suitable protective equipment. Store all garden chemicals out of the reach of children and pets.

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