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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. Dark, glossy green above and grey yellow-green beneath.
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.
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.
An olive tree can be grown for many uses, including:
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.
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.
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.
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.
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.
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.
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.
Pruning is best done early and often. Olives are also known to only fruit biennially if not regularly pruned.
Healthy trees growing in the right climate will be virtually problem-free. However, the following things may occur:
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 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 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.
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