Olive

About

Olives are sold in Britain as a Mediterranean flourish for a patio, and they survive here far better than they fruit.

The tree itself is hardier than most people expect, taking around -10 deg C in a sheltered position, and mature specimens have come through hard winters in southern England without protection. Cold combined with wet is what kills them, since roots sitting in saturated compost through a British January rot.

Fruiting is the disappointment. Olives need a period of winter cold to initiate flower buds, followed by a long hot summer to set and ripen the fruit, and Britain reliably delivers neither in the right combination. A tree here may flower and set a handful of olives in a hot summer, and they will rarely ripen fully.

Grow it for what it is. The trunk gnarls beautifully with age, the narrow grey-green leaves with silver undersides catch the light, it is evergreen, it needs almost no water, and it looks right in a large terracotta pot beside a warm wall.

Buy a tree with a good trunk if you can, since the character is in the wood.

Appearance and character

An evergreen tree reaching 3 to 8 m in Britain and 15 m in the Mediterranean, growing very slowly and living for centuries.

The trunk is the plant’s great asset. Smooth and grey when young, becoming deeply gnarled, twisted, hollowed and fissured with age, and an old olive trunk is one of the most sculptural things in the plant world.

Leaves are narrow and lance-shaped, 4 to 8 cm long, leathery, held in opposite pairs, dull grey-green above and silvery-white beneath with fine scales.

Flowers open in June and July, small, creamy-white and fragrant, in loose sprays from the leaf axils of the previous year’s wood.

Fruit is a drupe, 1 to 2.5 cm long, ripening from green through purple to black over several months, with a hard stone inside.

Growth is slow. An olive in a British garden puts on very little each year, which is part of why they are expensive.

Trees with substantial trunks sold in garden centres are usually imported mature specimens rather than anything grown here.

Where it is from

The Mediterranean basin, with domestication traced to the Levant several thousand years ago, and the wild ancestor is the oleaster, Olea europaea subsp. sylvestris.

The tree is central to Mediterranean civilisation. Olive oil was food, fuel, medicine, cosmetic and ritual across the classical world, and the olive branch as a symbol of peace reaches back to Greek and Hebrew tradition.

Olives are among the longest-lived trees in cultivation, and specimens in Crete, Portugal and Israel have been claimed at over two thousand years, with the trunk hollowing and regenerating repeatedly.

The plant is adapted to a climate of hot dry summers and mild wet winters, which is why British conditions suit it so poorly for fruiting and reasonably well for survival.

Flower bud initiation requires a period of about two months below roughly 10 deg C, followed by warmth. Britain provides the cold and rarely the following heat.

Olives arrived in British gardens as conservatory plants in the nineteenth century and became a mass-market patio plant in the 1990s, largely through imports of mature trees from Spain and Italy.

Xylella fastidiosa, a bacterial disease that has devastated olives in Puglia since 2013, is not present in Britain and is a serious plant health concern, which is why importing olive trees is regulated.

How it grows

Choose the warmest, sunniest, most sheltered position available. A south-facing wall, a courtyard or a sheltered terrace.

Grow it in a container in most of Britain, which lets you control the drainage and move it under cover if a hard winter is forecast.

Use a loam-based compost with at least a third added grit, in a pot with generous drainage holes and crocks, and stand it on pot feet so water runs away.

Plant in the ground only in the mildest coastal or urban areas, in sharply drained alkaline soil, on a raised bed or a slope if there is any doubt.

Keep it dry in winter. Move a container under the eaves, into a porch or against a house wall from November to March so it does not sit in wet compost. This matters more than any frost protection.

Wrap the pot with fleece or bubble wrap in a cold spell to protect the roots, which are the vulnerable part, and fleece the top growth below about -8 deg C.

Water sparingly. Olives are drought adapted and far more olives are killed by overwatering than by drought. Let the compost dry out between waterings.

Feed a container-grown tree monthly from April to August with a balanced or high-potash feed.

Prune in spring, after the worst frosts and before growth starts, in April.

Prune for shape and to open the centre. Olives fruit on the previous year’s wood, so light annual thinning rather than hard cutting is the approach where fruit is hoped for.

Remove crossing branches, thin the interior so light and air move through, and shorten over-long shoots.

Cut a neglected tree back hard if necessary. Olives regrow readily from old wood, which is one of their virtues.

Repot every three or four years into fresh gritty compost, or top-dress annually.

Do not expect fruit. Treat any olives you get as a bonus rather than a crop.

Through the seasons

Winter is the critical season, and the job is keeping the roots dry rather than warm. Move containers under cover from November to March.

Spring is pruning season in April, and growth starts once the weather warms.

Summer is the growing period, flowering in June and July, and this is when watering and feeding matter.

Autumn slows down, and this is the point to stop feeding and reduce watering before winter.

Care difficulty

Moderate, and the difficulty is winter management rather than anything in the growing season.

An olive in a well-drained pot in a sunny sheltered spot needs very little. Sparing watering, monthly feeding in summer, a spring prune and a repot every few years.

The winter is where they are lost, and almost always to wet rather than cold. A pot standing in a saucer of rain through January kills an olive that would have survived the frost.

Fruiting in Britain is unreliable to the point that it should not be the reason for growing one.

Leaf drop after a move, a cold snap or a change of position is common and usually recoverable.

Watering

Water sparingly. This is the single most important adjustment for anyone used to other container plants.

Let the compost dry out substantially between waterings, and check by pushing a finger into it rather than by a schedule.

Water more often through hot dry summer weather, and considerably less from October to March.

Never let it stand in water. Remove saucers in winter and stand the pot on feet so drainage is free.

A tree in the ground in a suitable position needs no watering once established.

Overwatering shows as yellowing leaves that drop, which is often mistaken for drought and watered further.

Warning signs, diseases and pests

Leaves yellowing and dropping in winter is most often waterlogging at the roots. Check the drainage, move the pot under cover, and reduce watering.

Sudden leaf drop after a move, a repot or a cold spell is shock. Keep it in a stable position, water sparingly, and it usually recovers.

Whole branches wilting and dying with dark staining in the wood is verticillium wilt, a soil fungus. Cut affected branches out well into clean wood, disinfect tools, and do not replant an olive in the same soil.

Brown limpet-like bumps on the stems and leaf undersides, with sticky leaves and black sooty mould, is scale insect, which is the commonest olive pest in Britain and worst under cover. Wipe off small infestations and treat in midsummer when the crawlers are moving.

Grey-white cottony masses in the leaf axils is mealybug.

Blackened crisp leaves after a hard winter is frost damage. Wait until late spring before cutting back, since olives often reshoot from apparently dead wood.

No flowers at all is the normal British experience, since the tree needs a specific sequence of winter cold and summer heat.

Flowers that set fruit which never ripens is a lack of summer heat.

Grey-green lichen on the trunk is harmless and is part of the character.

Growing environment

Full sun in the warmest, most sheltered position available.

Poor, gritty, sharply drained alkaline soil or a loam-based compost with a third added grit. Fertility is not what it wants and drainage is.

Hardy to around -10 deg C in a sheltered dry position, and far less so with wet roots. Southern and coastal Britain suit it best and cold wet inland gardens do not.

Allow a large container, at least 45 cm across, or 3 to 4 m of space in the ground.

It suits a large terracotta pot on a terrace, a courtyard, a sheltered south wall, a gravel garden in a mild area, or a conservatory.

Grow it with other Mediterranean plants that want the same treatment. Rosemary, lavender, cistus, phormium and bay all share the drainage and sun requirements.

Buy a tree with a good gnarled trunk if you can afford it, since that is the plant’s real asset and it takes decades to develop.

Its wildlife value in Britain is limited, since it flowers sparsely here.

Feeding

Feed a container-grown tree monthly from April to August with a balanced or high-potash liquid feed.

Stop feeding from September, so the growth hardens before winter.

Top-dress the pot with fresh compost each spring and repot fully every three or four years.

A tree in the ground on suitable soil needs no feeding.

Avoid high-nitrogen feeds, which give soft growth that suffers in winter.

Do not enrich the soil. Olives grow on poor stony ground in the wild and rich conditions produce soft growth without improving the plant.

Troubleshooting

Will it survive a British winter? In a sheltered position, usually. Olives take around -10 deg C. What kills them is cold plus wet roots, so keeping the pot dry and off the ground from November to March matters more than fleece.

The leaves have gone yellow and are dropping. Most often waterlogging rather than drought, which is the opposite of what people assume. Check the drainage, move it under cover, and water less.

Will it fruit in Britain? Rarely and not worth planning on. Olives need about two months of winter cold below 10 deg C to set flower buds and then a long hot summer to ripen the fruit, and Britain does not reliably provide the second part.

How often should I water it? Far less than you think. Let the compost dry out substantially between waterings, and reduce it sharply from October to March.

When do I prune it? In April, after the worst frosts and before growth starts. Thin the centre to let light and air through, and olives regrow readily from old wood if a hard cut is needed.

It dropped all its leaves after I moved it. Shock, which is common and usually recoverable. Put it somewhere stable and sunny, water sparingly, and wait.

Can I plant it in the ground? In mild coastal or urban areas with sharply drained alkaline soil, yes. Elsewhere a container is safer, because you can control the winter wet.

There are brown bumps on the stems and the leaves are sticky. Scale insect, the commonest olive pest here. Wipe small infestations off and treat in midsummer when the crawlers are active.

Can I eat the olives if I get any? They are inedibly bitter raw and need curing in brine, salt or lye. They are not toxic, and a handful of unripe British olives is unlikely to be worth the process.