Olive Tree Care: Why a Warm, Sheltered Tree Never Sets Fruit

The winter chill is the whole game

An olive sets flower buds only after it has spent a stretch of the winter cold. Roughly 200 to 300 hours between 35F and 50F (2C to 10C) is the usual requirement, and it works best when the nights are cold and the days noticeably warmer, which is why a tree pushed against a heated house wall can log the hours on paper and still produce nothing.

This is the single most common reason a healthy olive never fruits. A tree kept in a conservatory, a heated porch or a living room stays above 55F (13C) all winter, makes plenty of leaf, and forms no flower buds at all. It is not a feeding problem and no fertilizer will fix it.

So the rule for a container tree is simple: it goes outside for the winter, or into somewhere unheated and bright such as a cold greenhouse, a porch or against a north-facing wall. Bring it in only when a hard freeze is forecast, and put it back out when the freeze passes.

Record the coldest run of nights each winter alongside whether the tree flowered the following spring. After two or three years you will know exactly how cold your own site needs to get before your tree responds.

Wet compost kills olives, cold rarely does

A mature olive in the ground shrugs off temperatures down to about 15F (minus 9C). The trees that die in gardens almost never die of cold. They die because the roots sat in compost that stayed saturated through a wet, cold winter, and the root system rotted while the top looked fine.

The symptom is confusing because it looks like drought. Leaves go dull, then gray-brown, then hang on the tree without dropping. Gardeners water more, and the tree goes down faster. Before you water an olive that looks dry, push a finger two inches (5 cm) into the compost. If it is damp down there, the problem is the opposite of thirst.

Keep the compost gritty and free-draining, at least a third by volume of coarse grit or perlite. Stand pots on feet so water leaves the base, and never leave a saucer under an olive from autumn through to spring.

1. Check with a finger, not a schedule Water only when the top two inches (5 cm) are dry. In midsummer that may be every other day for a small pot; in winter it can be once a month or less.
2. Water hard, then stop When you do water, soak until it runs freely from the base, then let the pot dry down again. Frequent small splashes keep the surface damp and the deep roots dry.
3. Tip the saucer out Empty anything standing under the pot within an hour. In winter take the saucer away entirely.
4. Move the pot out of the rain Through a wet winter, a pot under the eaves or against a wall stays alive where an exposed pot in the open drowns.

Feeding: less than you think, and not late in the year

Olives evolved on thin, stony ground and a heavily fed tree makes long soft shoots at the expense of flowers. A balanced slow-release feed once in early spring, plus a second light dose in early summer, is enough for a tree in a pot. Trees in the ground in reasonable soil often need nothing at all.

Stop feeding by late summer. Nitrogen going in late pushes soft growth that has not hardened before the first frosts, and that soft wood is the part that dies back. Olives are also more sensitive to a shortage of nitrogen showing as uniformly pale leaves than to any of the trace elements, so if the whole canopy is yellowing evenly, feed in spring rather than reaching for a specialist product.

Yellow leaves in the middle of the canopy that drop in late spring are usually just the tree shedding two-year-old foliage. Yellowing across the whole tree, or on new growth at the tips, is worth acting on.

Light, wind and where the pot stands

Give an olive the brightest position you have. Six hours of direct sun is a minimum and eight or more is better. In shade the tree survives and grows thin, open, floppy growth, and flowers thinly or not at all.

Wind is less of a problem than most people expect and is actually useful at flowering time, since olive pollen travels on the breeze rather than on insects. A tree tucked into a still, sheltered corner sets less fruit than one standing in the open. What olives dislike is cold wind on soft new spring growth, so shelter matters in early spring and stops mattering by early summer.

What to write down this year

Olives run on a slow cycle and memory is not good enough. Keep four notes each year and the pattern becomes obvious by the third season: the date the tree first flowered, the coldest week of the preceding winter, whether you had a second olive nearby, and the weight or count of the fruit you picked.

Also note when you last repotted and when you last pruned hard. An olive that is pruned heavily one spring commonly skips the following year's crop, and without a note it is easy to blame the weather instead.