Why Olive Trees Bear Heavily One Year and Barely the Next
Olive harvests swing from feast to famine on a roughly two-year rhythm. It is not only the weather — a great deal of it is built into the tree itself, a self-imposed cycle called alternate bearing that no grower can quite switch off.
Olive trees are famously alternate-bearing: a heavy ‘on’ year is typically followed by a light ‘off’ year. Two things drive it. First, a big crop drains the tree’s reserves, leaving it less to invest the following season. Second, and more decisively, the developing fruit itself suppresses the buds that would become next year’s flowers — so a heavy autumn quietly programmes a thin spring. The result is a natural on-off pulse, layered on top of whatever the weather happens to do.
The on-year, off-year cycle
The key mechanism is worth spelling out, because it is not just ‘the tree gets tired’. As this year’s olives grow, they produce hormonal signals that inhibit the formation of flower buds for next year. So the very act of carrying a huge crop is what suppresses the following one: the tree cannot fully do both at once. A light year then lets it build reserves and set plenty of buds, which brings a heavy year, which suppresses the next — and round it goes. It is a rhythm the tree imposes on itself.
Why it matters to your bottle
This is why a single bumper or failed harvest tells you very little on its own — you have to watch the trend across several years, not the headline of one. It is also why, when an off-year collides with drought, disease or a pest outbreak, the shortfall can be severe: the natural low and the bad luck compound each other. When you see a dramatic ‘olive oil crisis’ story, ask whether it is a genuine failure or simply an off-year meeting a rough season — the two look alike from the supermarket shelf.
What growers can and can’t do
Growers soften the swing but cannot erase it. Careful pruning and, above all, fruit thinning in a heavy year — removing some of the crop so the tree does not exhaust itself or fully suppress next year’s buds — flatten the peaks and troughs. Good irrigation and nutrition help the tree recover faster. But the underlying biology remains: the olive keeps its own two-year calendar, and the grower’s job is to coax it toward something steadier, not to override it entirely.
| Pattern | Heavy ‘on’ year, then light ‘off’ year |
|---|---|
| Driver 1 | A big crop drains the tree’s reserves |
| Driver 2 | Developing fruit suppresses next year’s flower buds |
| Overlay | Weather, drought, pests stack on top |
| Worst case | Off-year colliding with a bad season |
| Grower’s tools | Pruning, fruit thinning, irrigation, nutrition |
| Bottom line | Can be softened, never fully erased |
What to remember
- Olives are alternate-bearing: a heavy year is usually followed by a light one.
- The main cause is this year’s fruit suppressing next year’s flower buds.
- A drained tree plus bud suppression makes the off-year worse.
- Judge oil by the trend, not a single bumper or failed harvest.
- Pruning and fruit thinning soften the swing but cannot erase it.
Alternate bearing: common questions
What is alternate bearing in olives?
The olive’s natural tendency to a heavy ‘on’ year followed by a light ‘off’ year, driven by reserve depletion and the suppression of next year’s flower buds.
Why does a big crop lead to a small one?
Because the developing fruit produces signals that inhibit flower-bud formation for next year, and a heavy crop also drains the tree’s reserves.
Is alternate bearing caused by weather?
No — it is built into the tree. Weather, drought and pests stack on top of the cycle and can make an off-year much worse, but they do not cause it.
Can growers stop alternate bearing?
Not entirely. Pruning, fruit thinning in a heavy year, and good irrigation and nutrition soften the swing, but the two-year rhythm cannot be fully erased.
How should this change how I read a harvest?
Judge oil by the trend across several years, not one headline. A single failed or bumper harvest often just reflects the natural on-year/off-year pulse.
It is a tree that thinks in decades, not seasons — one reason good growers, and honest prices, matter. Judge an oil by the year and the region, not by a single harvest’s headline, and remember that behind every steady supply is a tree being coaxed against its own two-year pulse. And when you read a dramatic ‘crisis’ story, ask the quiet question: is this a real failure, or just an off-year meeting a rough season? From the shelf, the two look identical.
A olives101 note on alternate (biennial) bearing in olive; mechanisms per horticultural sources.