Olives are not entirely hardy in most areas of the UK, and for this reason, consideration should be given whether to grow them in containers or not.
In mild areas olives have been known to crop outdoors if grown in a really sheltered position, having said that, growing plants in containers will allow the grower to be move the pots into a more protected spot in the garden if necessary.
Placing the pot / plant (in particular young plants) against a warm house wall or in an unheated greenhouse during prolonged cold weather can often prevent leaf drop, splitting bark or dieback.
Mature plants are more frost tolerant but can still be damaged when the temperatures fall below minus 10°C.
Plants damaged by frost will normally regrow from previously dormant buds, but flowering and fruiting for the season will be limited.
To flower and fruit successfully olives need at least two months of temperatures below 10°C in winter.
However for best results avoid prolonged cold weather below 7.5°C or winter temperatures above 15.5°C as both can prevent successful fruit production.
Olives will grow in a wide range of soil providing it is well drained.
The slow growing evergreen trees when grown outdoors can grow to 9-12m (30-40ft) tall, with a spread of 7-9m (20-30ft)
In containers they can be grown to more manageable dimensions.
As indicated above plants are best grown in pots that can be placed outdoors in summer and brought into a cold glasshouse for winter.
It is recommended to start off with the smallest pot possible, then potting on as necessary.
Ideally, fill the pots with loam-based compost, such as John Innes No.3 or similar, mixed with grit at a ratio of 4:1 for drainage.
Ensure that the pot/s are well crocked at the base of the pot, and are raised off the ground to allow them to drain fully.
As indicated above growing in pots is the best method, however given the right conditions, a certain amount of success can be had outdoors.
Supplementing the growing area with windbreaks can help to create ideal conditions but be careful that the wind breaks do not create frost pockets!
They are happy in a wide range of soils, providing they are alkaline and well drained.
Soils that are very fertile are likely to result in excessive vegetative growth.
Planting distances can vary according to the variety being grown.
Expect these distances to be around 7-10metres(20-30ft) apart (each way)
(Both Outdoors and in Containers:)
Top-dress a slow release nitrogen fertiliser(14 gms [ ½oz] per sq m) to each tree up to three times per year.
Supplement these feeds with monthly high potash liquid feeds to encourage fruiting.
Although drought tolerant, olives benefit from regular watering in dry spells, particularly in the first two to three years after planting.
Outdoors: Water olives regularly during dry periods,
Mulching with organic material and keeping the planted area free of weeds is also beneficial.
Watering of containers can be critical to the overall health of the plant/s
Although they are drought tolerant they will need watering and feeding regularly when in growth.
Reduce watering in winter, but do not allow the compost to dry out completely.
Pruning and Training:
Prune newly planted olives by removing the leading shoot when it is about 1.5m (5ft) tall.
Train 3 to 5 strong laterals to provide the basic branch structure.
Fruits are produced on one year old wood, and mostly at the edges of the tree canopy, so remove older branches to encourage the growth of new shoots to cater for attribute.
Olives produce a very insignificant cream flower, and are usually pollinated by insects and or the wind.
High humidity levels can inhibit pollination.
Note: Most cultivars are self-fertile, but pollinators may be necessary to increase fruit yield particularly in cool seasons.
Fruit thinning may be necessary, if the trees show signs of biennial bearing, this is done by hand when required.
The fruits may be gathered while they are still green, or when they are fully ripe and have turned black.
Pests and Diseases:
Olives grown in the open may be affected by Scale insect and Verticillium wilt.
Trees grown under cover may be affected by whiteflies, thrips, and red spider mites.