Olive tree

Light and exposure

The olive tree wants full sun, no compromise. Give it the warmest and brightest spot you have: the south side of a terrace, a well-exposed wall, a corner that bakes all day. The less sun it gets, the more it stretches out, thins and loses that dense habit that is its whole charm.

In a pot, the advantage is clear: you follow the light and bring the tree into shelter for the winter. In open ground, keep it for a truly sheltered microclimate, backed against a south-facing façade that gives back its heat at night. In half-shade, under our already sun-starved sky, it just languishes.

Watering

This is where most failures play out. The olive tree fears an excess of water far more than drought. In a pot, water regularly in summer, but let the substrate dry out well between two passes: you wait until the surface is dry over several centimetres before giving water again. A thirsty olive tree holds on without flinching, a drowned olive tree rots at the roots.

In winter, cut back almost everything. In shelter and cool, the tree is ticking over and consumes next to nothing: a soil that stays damp and cold means guaranteed rot. A little water now and then so the root ball does not dry out completely is more than enough.

Soil and repotting

The watchword is drainage. The olive tree grows in the stony, poor soils of its homeland, it hates heavy soils that hold water. In a pot, build a mix that lets the water run through: potting soil, a third of coarse sand or pozzolana, and a good layer of clay balls or gravel at the bottom. In open ground, only a light, raised soil suits it, otherwise correct with gravel and sand at planting.

Repot into a large pot, heavy and stable, with a hole at the bottom. A container that is too tight dries out too fast in summer and tires the tree. Repot every two to three years in spring, renewing the substrate and checking that nothing is blocking the drainage. A pot that keeps water at the bottom, under our rains, kills the olive tree more surely than the cold.

Temperature and humidity

The critical Belgian point comes down to one sentence: it is not so much the cold that threatens the olive tree here, it is cold combined with damp. Dry and well established, it takes short frosts of minus 8 to minus 10 degrees. But our mild, grey and waterlogged winters are more fatal to it than a genuine dry frost snap, because the water-soaked roots freeze and rot.

In practice, in zone 8a, you do not take chances. From November to April, the potted olive tree spends the winter in cold, bright, frost-free shelter: an unheated conservatory, a cold greenhouse, a bright garage. You are not after warmth, you are after frost-free and light. In open ground, reserve it a very sheltered and drained microclimate, and protect trunk and stump with horticultural fleece and a good mulch on nights of hard frost, without ever guaranteeing that it comes through a harsh winter.

Pruning and upkeep

Prune in late spring, once all risk of frost has passed and growth has clearly resumed. The aim is to open up the centre and keep an open, goblet habit: you remove dead wood, crossing branches and those cluttering the heart, so that light and air circulate. An overly dense olive tree stays damp and attracts trouble.

The rest of the care is light. A feed for citrus or Mediterranean plants from spring to the end of summer supports a potted tree, whose substrate becomes exhausted. Clean up the yellow leaves fallen at the base so as not to leave damp lying around, and watch the underside of the foliage where pests lodge.

Pests and diseases

In our damp climate, the real danger comes from water. Root rot from excess watering or from a soil that does not drain is the leading cause of death of the olive tree here: dull leaves, a tree that declines for no apparent reason, often too late by the time you notice it. In a damp winter, leaf drop is common, sometimes harmless if the tree is simply stressed, more serious if the roots are suffering.

On the pest side, watch for scale insects, common in pots and under shelter: they cling to the stems and the undersides of the leaves, secrete a honeydew on which sooty mould settles, that black, sticky deposit. The olive moth can also attack leaves, flowers and fruit. Hose down the foliage, apply black soap or a white oil on the scale-insect outbreaks, and ventilate to cut short the damp that favours all this.

Propagation

Cuttings are the most accessible route. In summer, take semi-ripe shoots of fifteen centimetres, remove the lower leaves, dip the base in a rooting hormone and plant in a very free-draining sandy mix, under cover and in the warm. Rooting is slow and temperamental, count on several months and accept failures: that is normal with the olive tree.

Sowing from seed exists but calls for patience and gives trees different from the parent, often long to form. For most gardeners, the simplest thing remains to buy an already-formed specimen at a garden centre and put it in the right conditions. A well-managed olive tree lives a very long time, the initial outlay pays for itself over decades.

Month-by-month care calendar

Green Hub tips

• Drainage above all: a pot that keeps water at the bottom kills the olive tree more surely than the cold. Sand, pozzolana and clay balls at the bottom, always.
• Do not leave it outside in winter in zone 8a. Bring it in frost-free and bright from November to April, it is the cold damp that kills it, not the dry frost.
• Water little and let it dry out between two. In winter in shelter, almost nothing: a dry olive tree comes through the winter, a drowned olive tree rots.
• Do not aim for an olive harvest here. It is a fine ornamental tree with silvery foliage, take it for what it is.