Olives (Olea europaea) are evergreen trees that will add a Mediterranean touch to the garden. They are suited to garden or container cultivation, and may produce fruit in mild regions and warm summers in the UK.
If you have a protected city garden or live in a mild area, olives can be grown outdoors as long as you give them a sunny position and plant them in well-drained soil, for example, against a warm wall would be ideal. IN cold or northern regions winter protection in a conservatory for example, will be required.
Once established they are extremely drought-tolerant, but plants will do better if watered regularly in dry spells during the growing seasons. To encourage strong growth, it’s a good idea to feed each spring with a general fertiliser, such as Vitax Q4.
Olives naturally shed their older leaves in spring (April in the UK) as new growth begins.
Olives are not entirely hardy in the UK, and will be damaged by temperatures below -10°C (14°F). So, in colder areas of the country, you can grow olives in large (60cm, 24ins) diameter and depth) containers. Plant in a well-drained mix of compost, such as loam-based John Innes No 3 with 20 percent by volume added horticultural grit. You can place containers outdoors in summer and then move into a cold conservatory, porch or greenhouse over winter.
Although they can cope with dry periods, olives in containers need regular watering and feeding to produce fruit. During the growing season keep the compost moist and feed with a balanced liquid fertiliser such as Phostrogen, every month. In winter, you can reduce watering, but don’t let the compost dry out completely.
Pruning and training
Olives grow very slowly, so don’t require much pruning at all. If needed, in late spring or early summer, remove dead, diseased or dying branches. At the same time, thin out branches to allow light into the centre of the tree and remove any branches that spoil the shape. Avoid pruning too hard as this will result in the over-production of non-fruiting water shoots.
Container-grown plants may need additional summer pruning to keep their size in check. When plants in containers get to about 1.5m (5ft), pinch out the tips to encourage branching.
Growing olives for fruit
In order to initiate flowers and fruit, olive trees need a two-month period of cold weather (with temperatures below 10°C (50°F). They also need a fluctuation between day and night time temperatures. Plants kept indoors are therefore unlikely to flower.
Very dry soil conditions can also inhibit flowering, even if the tree is able to tolerate such conditions. Watering during dry spells between February and May is therefore crucial for fruit production.
Prolonged cold weather (below 7.5°C or 45°F) can also inhibit fruit production.
Growing more than one cultivar will increase cross-pollination and improve yield, although even a single tree should produce some fruit, olives being self-fertile.
Fruit is produced at the tips of the previous year’s growth, so excessive pruning will also prevent fruiting. Thinning of the crop is recommended, reducing the fruit numbers to three or four per 30cm (1ft) of branch within three weeks of flowering, in order to ensure that the crop will ripen and not drop prematurely.
Ripe black olives can be picked and eaten raw, but taste quite different from commercially sold olives, which are usually picked unripe and green, or black and ripe, but are then cured to produce an edible product.
Named cultivars are propagated by grafting. This is the preferred method in olive growing regions.
Olea europaea can also be increased by taking semi-ripe cuttings in summer.
It will take at least four years for young plants to bear fruit.
Garden centres and nurseries should stock Olea europea, but if you are looking for a specific cultivar, try a specialist grower. Available varieties include:
- Olea europaea ‘Sativa’ – small white, scented flowers in late spring and summer
- O. europaea subsp. africana – smaller fruit and dark green, glossy leaves
- O. europaea ‘Frantoio’ – popular Italian variety used for making olive oil
Plants are not entirely hardy in the UK and long spell of cold weather can cause leaf drop, splitting bark and dieback. Even mature plants, which are fairly tolerant of frost, will be damaged once temperatures dip beneath -10°C (14°F). Any plants that are damaged should regrow from dormant buds along their branches, but their flowering and fruiting performance will be reduced that season.
Poorly-drained soil conditions can lead to root disease such as Verticillium wilt or Phytopthora root rot. Honey fungus may cause plant death.
Scale insect is sometimes a problem, as is the disease olive scab which causes ring-spot symptoms on the foliage.