Welcome to Top of the Crops! Today, you will learn about growing olives in a polytunnel. Discover professional tips and advice on how to grow olives in the UK with us, and for further gardening advice, check out Polytunnel Gardening.
Olive trees are of course staple crops of Mediterranean climate zones. They are sometimes grown in the UK and our changing climate is making that increasingly more viable for many gardeners. However, growing olive trees that actually fruit is more challenging. A polytunnel can make that a little easier and more within reach for gardeners in the British Isles.
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Olive trees, Olea europaea, are small, evergreen trees or shrubs native to the Mediterranean basin. They produce small, green fruits that must be processed before they can be eaten. These have been used as a food source in their native range for thousands of years and are now enjoyed in many regions around the world.
Though not ideally suited to our climate zone, olives can be grown here as long as the right placement is chosen and the right growing methods are employed. The key is to mimic Mediterranean conditions as closely as possible.
This means providing as warm and sunny a location as possible, with fertile and yet free-draining soil or growing medium. Olive trees will need 8 plus hours of sun each day – the more the better.
Olive trees can be grown outside year round in the ground in only the most southerly and sheltered of UK gardens. Often, they are planted in pots so that they can be moved indoors over the winter months and kept in a frost-free location.
An in-ground position is best where possible, however, which means that a polytunnel can be a good idea. The polytunnel can potentially keep an olive frost free, prevent waterlogging issues due to heavy rains, and provide the warm and sunny environment that these trees need.
First, choose an olive tree. You can purchase trees of many sizes, from small saplings to gnarled old beauties. Of course, the size and age of the tree will determine the cost.
Select a suitable planting location. If planting in the ground, dig a planting hole large enough to accommodate the root ball, so that the top of the root ball is just above ground level. Firm the soil back around the roots and water in your olive tree watering deeply and well but making sure that excess water can drain away freely.
Don't add compost or other soil amendments to the planting hole as a young olive tree must adapt to the native soil in order to thrive. However, you may wish to mulch around the tree to protect the soil and conserve soil moisture.
If you are planning on growing on an olive tree in a container, make sure you choose one that is of sufficient size to accommodate the roots. Usually, you will need a pot at least 35-40cm in depth and diameter. Fill this with a gritty loam-based potting mix with some organic fertilizer mixed in.
Most olive trees are self-fertile meaning that they can produce fruits even without a pollination partner. However, if you can grow two or more compatible trees that can cross-pollinate, yields will often be improved.
If you wish to grow olives you will need:
An olive tree
A suitable growing location/ growing medium and perhaps container.
A garden spade to dig your planting hole.
Pruning tools.
Gardening gloves
Facility to water your olive tree when needed.
Organic materials for mulching/ fertility.
Growing olives successfully is largely a case of selecting the right variety, placing it in the right location, and caring for the tree correctly over time. Watering and ensuring a healthy soil/ growing medium over time are key care elements to consider. Pruning and training are also important considerations.
Olive trees are not the easiest plants to propagate at home. But you can potentially try to propagate olive trees by taking semi ripe cuttings in summer, or hardwood cuttings in the late autumn or winter.
Harvesting olives can be done while the fruits are still green, or you can harvest when (if) the fruits ripen and turn fully black in the late autumn. Fully ripe olives are not necessarily something most can expect when growing these mediterranean trees in the UK.
The olives you pick, whether still green or fully ripened, need to be processed in a particular way before they are eaten. So you can't just expect to harvest olives you can eat from the tree.
Green olives need to be soaked in salted water for a number of days in order to make them palatable. This process will remove most of the bitterness. Black olives are cured dry, in salt, for a number of weeks until they are fully dehydrated, then stored in brine or olive oil.
Once the olives have undergone this treatment, they can be used in a range of recipes.
Caring for olive trees, of course, involves paying careful attention to the tree and its basic needs.
Watering is among the most important considerations when it comes to making sure that an olive tree's needs are met.
In the spring and summer months, newly planted olive trees and those in containers or which don't have access to natural rainfall will need to be watered regularly.
You should aim to make sure that the soil or growing medium is moist but ensure that excess water always drains away freely. Good drainage is crucial as olive trees can tolerate dry conditions but not waterlogging.
In autumn and winter, you should cut back on water provided, and ensure that the tree is not exposed to too much rain if it is outdoors. Don't allow waterlogged conditions to arise as this is more likely to be a problem for olive trees than cold temperatures at this time of the year.
Olive trees grown in the ground can be grown in any soil type except heavy clays with poor drainage. As long as the soil is free draining, issues should not arise. Though the ideal pH is one that is slightly alkaline, these trees are tolerant of a range of growing conditions and can grow even in a nutrient-poor soil.
While olive trees are not particularly hungry plants and don't require a very fertile soil, they do need some help to perform at their best in our climate, and will need feeding, especially when they are grown in pots.
Feed a mature olive tree with an organic mulch around its base, and feed your tree, especially one in a container, with a well-balanced, organic, liquid plant feed every month between April and September to encourage a good yield of fruits if performance is poor. Repot container grown trees with new growing medium every 2-3 years.
Olive trees, while young, can be trained to have an open-centred form. When planting, if starting with a young whip, cut off the central shoot with a sloping cut, just above a bud around 1.5m above the ground. Remove any lateral shoots on the bottom 50cm or so and cut back higher laterals to half their length.
During the tree's first summer, the main side branches should then be cut back to around 20cm of the start of the growth of the present year, cutting back to an outward facing bud. New shoots or laterals should be cut back to around 15cm. The central leader should be left alone.
The second spring after planting the olive tree, the central leader should be cut back to around 2/3 of the growth of the previous year. It should be cut back by around the same amount each year until it reaches the desired height.
Olive trees are typically maintenance pruned early in the spring. The goal is to keep cutting to a minimum, while ensuring an open centred canopy, attractive shape and good health. Remove any dead, damaged or diseased material, and branches that cross towards the centre of the canopy.
If you want to restrict the size of the tree, prune the tips of the main branches, cutting back to a good replacement shoot each year. Tip prune the central leader to around 5cm of the previous year's growth.
Some cultivars recommended for growers in the UK are:
Most of the problems experienced by growers of olive trees in the UK revolve around environmental conditions not being right.
Olive trees are pretty hardy on the whole, for example, but can suffer if temperatures fall below around minus 10ºC. The foliage and bark can be damaged by the cold, but though fruit production will likely be reduced the following season, the tree should recover.
Waterlogging can also cause issues, such as phytopthora root rot. Other fungal problems like verticillium wilt, honey fungus, olive leaf spot, olive anthracnose, and olive scab can also take hold of these trees. And there is also a bacterial issue known as olive knot. Practicing good plant hygiene and clearing away affected material promptly can help reduce spread of any issues.
Place an olive tree in the ground inside a polytunnel, or keep one in a container inside the space.
In milder regions, the olive tree might be placed outside in summer, and moved into the polytunnel for protection only during the winter months.
Provide good ventilation and ensure access for pollination at the crucial time of year when olive trees are in flower.
Create a fruit tree guild around the olive tree to protect and aid the fruit tree in a range of different ways. Some good plants to place around an olive tree include globe artichokes or cardoons, tree germander, curry plant, marjoram, hyssop, lavender, thyme and other mediterranean herbs. These are just some examples of plants that can aid olives while also looking great around the base of the tree.
Olive Magazine. (n.d.) Easy Olive Recipes. [online] Available at: https://www.olivemagazine.com/recipes/collection/best-ever-olive-recipes/ [accessed 14/12/23]
