Olives are a Mediterranean plant but in sheltered spots, in the southern reaches of the UK, can be grown outside. A polytunnel, however, can extend the range of areas where olive trees can successfully be grown in the UK. Growing in a containers will allow you to move around your olive tree as required during the different seasons. A polytunnel will protect your olive tree from chilly north and east winds and provide a sunny, sheltered growing position.
Olive trees are usually bought as saplings or propagated from stem cuttings. Hardwood cuttings can be used – sections of one or two year old wood about 30cm long. If you are taking your own cuttings, place these in a pot to a depth of around 15cm. In a temperature of 13-21 degrees, you can expect your cuttings to take root in around 30 days.
Olive trees require a loamy growing medium that is free-draining, so plants do not become waterlogged during the wettest portion of the year. If you are growing in a container, be sure not to choose one that is too large, as over-potting can be detrimental.
It is a good idea to feed your olive tree with an organic fertiliser, such as seaweed based feed, every couple of weeks between May and September. Keep the soil in your containers moist throughout the growing season but do not over-water. Pruning can also help to keep your olive tree healthy and to maintain size and habit. Undertake light, formative pruning in mid-spring and then undertake any heavier pruning that is required in early or mid-summer. Olive trees need a chance to heal wounds and recover before the dormant winter period.
Insulate the pot in the winter to prevent the roots from freezing – you can use bubble wrap in a few layers around the sides of your container. In the coldest parts of the UK, you may also have to provide a little extra protection in the form of horticultural fleece on the trunk and crown of the tree, though this will not be necessary in most parts of the UK, as olives are a surprisingly hardy plant.
In southern portions of the UK, olive trees kept in a frost-free but cool polytunnel can, if you wish, be moved outside to a sunny and sheltered position after all risk of frost has passed in your area.
Olives do need to be cool in the winter (below 10 degrees) in order for flowers to form thereafter. However, temperatures below 7.5 degrees over the prolonged period may inhibit fruit production. Olives are self-fertile so one tree on its own should be able to bear fruit when given the right growing conditions.
Most olives cannot be eaten straight from the tree and must be prepared in order to make them palatable. The olives you buy have been cured before sale.